View source for Mekosuchinae

{{Short description|Extinct subfamily of reptiles}}
{{Automatic taxobox
| fossil_range = [[Eocene]] - [[Holocene]], {{fossilrange|56|0.003}}
| image = Mekosuchinae.png
| image_caption = Four members of Mekosuchinae: ''Paludirex'', ''Baru'', ''Mekosuchus'' and ''Quinkana''
| taxon = Mekosuchinae
| authority = Willis, Molnar & Scanlon, 1993
| type_species = {{extinct}}''[[Mekosuchus inexpectatus]]''
| type_species_authority = [[Jean Christophe Balouet|Balouet]] & Buffetaut, 1987
| subdivision_ranks = [[Genus|Genera]]
| subdivision = * ''[[Australosuchus]]''
* ''[[Baru]]''
* ''[[Kalthifrons]]''
* ''[[Kambara]]''
* ''[[Mekosuchus]]''
* ''[[Paludirex]]''
* ''[[Quinkana]]''
* ''[[Trilophosuchus]]''
* ''[[Ultrastenos]]''
* ''[[Volia]]''
}}
'''Mekosuchinae''' is an extinct [[clade]] of [[crocodilia]]ns from the [[Cenozoic]] of [[Australasia]]. They represented the dominant group of crocodilians in the region during most of the Cenozoic, first appearing in the [[fossil record]] in the [[Eocene]] of Australia, and surviving until the arrival of humans: the [[Late Pleistocene]] on the Australian continent and during the [[Holocene]] in the Pacific islands of [[Fiji]], [[New Caledonia]] and [[Vanuatu]].

Mekosuchine crocodiles are a diverse group displaying a great variety of shapes and sizes. Some taxa, like ''[[Baru]]'' and ''[[Paludirex]]'', were large semi-aquatic ambush hunters, though the two genera likely differed significantly in their hunting methods. The medium-sized ''[[Australosuchus]]'' may have been relatively cold-resistant and taxa like ''[[Trilophosuchus]]'' and ''[[Mekosuchus]]'' are renowned for their small size. One of the most distinct mekosuchines was ''[[Quinkana]]'', with its altirostral (deep) skull and blade-like serrated teeth.

There is some question around the lifestyle of mekosuchines. Based on skull shape, many taxa are semi-aquatic and most mekosuchines have relatively conservative hip morphology, although other factors might indicate greater terrestrial capabilities. The [[humerus|humeri]] are straighter than in modern crocodiles, allowing them to perform the so-called "[[High walk|highwalk]]" more easily. ''Mekosuchus'' and ''Trilophosuchus'' are commonly regarded as more terrestrial, perhaps similar to [[Paleosuchus|dwarf caiman]]s and [[dwarf crocodile]]s, while ''Quinkana'' displays a skull shape very similar to terrestrial crocodylomorphs like [[Sebecidae|sebecids]] and [[Planocraniidae|planocraniids]]. In the case of ''Quinkana'', this interpretation is mostly hindered by the near complete lack of [[wiktionary:postcranium|postcrania]]l material, with the exception of some isolated hip bones which suggest the presence of a mekosuchine with erect limbs in the [[Riversleigh World Heritage Area]], where ''Quinkana'' was found.

Mekosuchines were historically considered to be true [[crocodile]]s (of the [[family (biology)|family]] [[Crocodylidae]]), but modern research favors the idea that they either diverged before the split between [[Gavialidae|gharials]] and crocodiles or that they are a sister group to Crocodylidae. Some recent studies have even played with the idea that [[Orientalosuchina]], a clade of small crocodilians from the Cretaceous to Paleogene of Asia, might be a part of Mekosuchinae. Regardless of their origins, mekosuchines rapidly diversified between their first appearance during the Eocene and the Oligocene-Miocene boundary, when as many as five different genera of very different morphology all inhabited the freshwater environments and forests of the Riversleigh.

Mekosuchines underwent a decline in post-Miocene Australia, with most genera believed to have gone extinct due to an especially severe period of [[aridification]]. While mekosuchines recovered during the [[Pliocene]], the continuous decline of inland freshwater systems and the associated terrestrial biomes gradually lead to the decline of the family. By the Pleistocene only the genera ''Quinkana'' and ''Paludirex'' still inhabited [[mainland Australia]], alongside the more recent true crocodiles. After the demise of the last mainland mekosuchines, the group survived on Vanuatu and New Caledonia until the Holocene. In both instances the extinction of mekosuchines happens around roughly the same time as the arrival of [[humans]], though it is unclear how much of a part, if any, they played in these events. For the mainland taxa it is argued that their disappearance was entirely related to [[climate change]], with the pattern of extinction matching the disappearance of [[river basin]]s but not the appearance of humans. Things are more complex for the island forms, with some researchers questioning how much ''Mekosuchus'' and humans truly overlapped. If humans [[Human impact on the environment|played a role]] in the extinction of the last mekosuchines, it could have been either directly due to [[overhunting]] or more indirectly through [[habitat destruction]] and [[invasive species]] like [[rats]].

==History of discovery==
{{multiple image
|align = left
|total_width = 250
|perrow=2/1

|image1 = Charles Walter de Vis (1829–1915).jpg

|image2 = Pallimnarchus syntype fossils.jpg

|image3 = Pallimnarchus lectotype.jpg

|footer = De Vis (left) and the material used to coin the name ''Pallimnarchus'' (right, bottom).}}

===Early finds===
Although the family Mekosuchinae was not established until the 1990s, fossil material belonging to members of this clade had been known from the Australian continent for a long time. The first material now recognised as belonging to this group of crocodilians was described in 1886 by English zoologist [[Charles Walter De Vis]]. The fossils, discovered in the [[Darling Downs]] in [[Queensland]], consisted of skull and postcranial fragments that De Vis dubbed ''[[Pallimnarchus|Pallimnarchus pollens]]''.<ref name=DV86>{{cite journal |last1=De Vis |first1=C.W. |author1-link=Charles Walter De Vis |year=1886 |title=On remains of an extinct saurian |journal=Proceedings of the Royal Society of Queensland |volume=2 |pages=181–191}}</ref> De Vis himself only coined the name "out of convenience", admitting that he was too unfamiliar with the Cenozoic crocodilian fossil record to be certain that his find represented an animal distinct from any other taxa known at the time. Later research has even shown that the material belonged not only to multiple individuals but multiple different genera, with various bones since then having been referred to ''Paludirex'' and ''Quinkana'' respectively. Regardless of De Vis' caution regarding the taxon, the name ''Pallimnarchus'' eventually came to be widely used by other authors.<ref name=M82b>{{Cite journal|last1=Molnar|first1=R.E.|year=1982|title=Pallimnarchus and other Cenozoic crocodiles in Queensland|url=https://www.biodiversitylibrary.org/part/303535|journal=Memoirs of the Queensland Museum|volume=20|issue=3|pages=657–673}}</ref><ref name=R20/>

===Renaissance===
Despite these early finds, research on genera that we now classify as mekosuchines would grow quiet during the first half of the 20th century, with the lack of published research focused on [[Australasia]]n crocodilians during the middle of the century leading to a 40-year hiatus. This period would come to an end in 1977 with the publications of Max Hecht, Michael Archer and [[Ralph Molnar]], all of which reported on fossil material collected from cave deposits in northern Queensland.<ref name= M04>{{cite book|author=Molnar, R. E.|title=Dragons in the Dust: The Paleobiology of the Giant Monitor Lizard Megalania|url=https://books.google.com/books?id=AvPHRQYqEcQC|year= 2004|publisher= [[Indiana University Press]]|isbn= 0-253-34374-7| pages= 174–175 | oclc = 52775128}}</ref><ref name= A78>{{Cite journal|last=Archer|first=Michael |date=1978 |title=Quaternary vertebrate faunas from the Texas Caves of southeastern Queensland|url=https://www.biodiversitylibrary.org/page/48737733|journal=Memoirs of the Queensland Museum|volume=19|issue=1|pages=61–109}}</ref><ref name= M77>{{Cite journal|last=Molnar|first=R. E.|date=1977-07-01|title=Crocodile with Laterally Compressed Snout: First Find in Australia|journal=Science|volume=197|issue=4298|pages=62–64|doi=10.1126/science.197.4298.62|pmid=17828894|bibcode=1977Sci...197...62M|s2cid=41255154|issn=0036-8075}}</ref> This material encompassed both more fragmentary remains as well as better preserved ones, including a nearly complete rostrum recovered from the Tea Tree Cave. The material was quickly noted for its distinct morphology, bearing some resemblance to terrestrial crocodylomorphs like [[sebecosuchians]] and [[Planocraniidae|planocraniids]]. Following the discovery of even more fossil fragments, the taxon was named ''Quinkana'' in 1981, though early interpretations linked it to the [[Paleogene]] planocraniids rather than the already established ''Pallimnarchus''.<ref name=M81/>

In 1982, just a year later, Molnar published a paper focused on ''Pallimnarchus'', attempting to revise the genus by establishing a [[lectotype]] specimen to compensate for the fact that De Vis did not establish a [[holotype]].<ref name=M82b/> Around the same time, reports of crocodilian fossil material came out of [[New Caledonia]],<ref name=B91>{{Cite book|last1=Balouet|first1=J.C.|year=1991|chapter=The fossil vertebrate record of New Caledonia|title=Vertebrate Palaeontology of Australasia|editor-last1=Vickers-Rich|editor-first1=P.|editor-last2=Monaghan|editor-first2=J.M.|editor-last3=Baird|editor-first3=R.F.|editor-last4=Rich|editor-first4=T.H.|publisher=Monash University Publications Committee, Melbourne, Australia|url=https://www.biodiversitylibrary.org/item/123394#page/1405/mode/1up|pages=1381–1409|isbn=978-0-909674-36-6 }}</ref> these leading to the description of ''Mekosuchus'' by French paleontologists [[Jean-Christophe Balouet]] and [[Eric Buffetaut]] in 1987. Like with ''Quinkana'', the distinct morphology of ''Mekosuchus'' initially obscured its relationship to modern crocodilians, with the team placing it in the newly named family Mekosuchidae, which they placed as an early branch of [[Eusuchia]] and the [[sister group]] to the three extant groups of crocodilians (crocodiles, gharials, alligators and caiman).<ref name=BB87/>

===Recent work===
[[File:Geoff Vincents Specimen.jpg|thumb|Geoff Vincent's specimen was instrumental in the redescription of ''Pallimnarchus'' as ''Paludirex''.]]
The 1970s and 1980s set the groundwork for what would be a period of increased interest in Australasian crocodilians during the 1990s and early 2000s. In addition to Hecht, Archer and Molnar, a variety of other authors would publish on crocodile fossil material during this time, many of which going on to become quite prolific in the study of mekosuchines. These include [[Paul Willis]], [[Steven Salisbury]] and [[Dirk Megirian]]. Following the description of ''Baru'', scientists began to recognize shared traits among the fossil crocodiles of Australia, with Willis and colleagues proposing the presence of what they dubbed the  Australian Tertiary crocodylian radiation.<ref name=WMM90/> This concept initially included the three mainland taxa ''Baru'', ''Quinkana'' and ''Pallimnarchus'' and was later expanded to include ''Australosuchus'' as well, named a year later in 1991.<ref name=WM91/>

The concept of the Australian Tertiary crocodylian radiation would come to be replaced by the subfamily Mekosuchinae in 1993, defined by Willis, Molnar and John Scanlon as a [[subfamily]] of the [[Crocodylidae]].<ref name=WMS93/> The name was intentionally carried over from the monotypic Mekosuchidae of Balouet and Buffetaut,<ref name=BB87/> with Willis and colleagues meaning to preserve the seniority of the name while adapting it to more accurately reflect their supposed position among crocodilians at the time. In terms of composition, the only new taxa included were ''Kambara'', named in the same paper, and ''Mekosuchus'', the namesake of the clade.<ref name=WMS93/> Other mekosuchines recognized during the 1990s were ''Trilophosuchus'', named not long after the family was described in 1993,<ref name=WPMA93/> as well as three additional species of ''Quinkana'',<ref name= WM96/><ref name=W97b/><ref name= M94/> two species of ''Baru,''<ref name=W97b/> and one species each of ''Kambara'',<ref name=SW96/> ''Pallimnarchus,''<ref name=WM97/> and ''Mekosuchus''.<ref name=W97b/>

This trajectory more or less carried over into the 2000s and 2010s, seeing the description of two more ''Kambara'' species,<ref name=H05/><ref name=B09/> two more ''Mekosuchus'' species were described,<ref name=W01/><ref name=M02/> alongside entirely new genera such as ''Volia'',<ref name=M02b/> ''Kalthifrons,''<ref name=Ka17/> and ''Ultrastenos''.<ref name="Stein2016"/> Another spike in research occurred during the late 2010s and early 2020s with the publication of multiple papers helmed by [[Jorgo Ristevski]], whose work includes a complete overhaul of the genus ''Pallimnarchus'', coining the new name ''Paludirex'' in its place to bring stability to the taxon,<ref name=R20/> two studies on the cranium of ''Trilophosuchus,''<ref name=R22>{{Cite journal|last1=Ristevski|first1=J.|year=2022|title=Neuroanatomy of the mekosuchine crocodylian Trilophosuchus rackhami Willis, 1993.|journal=Journal of Anatomy|volume=241|issue=4|pages=981–1013|doi= 10.1111/joa.13732 |pmid=36037801 |pmc=9482699 }}</ref><ref name=R23a>{{Cite journal |last1=Ristevski |first1=Jorgo |last2=Weisbecker |first2=Vera |last3=Scanlon |first3=John D. |last4=Price |first4=Gilbert J. |last5=Salisbury |first5=Steven W. |date=February 2023 |title=Cranial anatomy of the mekosuchine crocodylian Trilophosuchus rackhami Willis, 1993 |journal=The Anatomical Record |language=en |volume=306 |issue=2 |pages=239–297 |doi=10.1002/ar.25050 |pmid=36054424 |pmc=10086963 |issn=1932-8486}}</ref> and a summary of Australasian crocodylian research co-authored with several other researchers previously involved in mekosuchine research.<ref name=R23b>{{Cite journal|last1= Ristevski|first1=J.|last2=Willis|first2=P.M.A.|last3=Yates|first3=A.M.|last4=White|first4=M.A.|last5=Hart|first5=L.J.|last6=Stein|first6=M.D.|last7=Price|first7=G.J.|last8=Salisbury|first8=S.W.|year=2023|title=Migrations, diversifications and extinctions: the evolutionary history of crocodyliforms in Australasia|journal=Alcheringa: An Australasian Journal of Palaeontology|volume=47 |issue=4 |pages=1–46 |doi=10.1080/03115518.2023.2201319|s2cid=258878554 |doi-access=free|bibcode=2023Alch...47..370R |hdl=1959.4/104056|hdl-access=free}}</ref> 2023 saw the description of ''Baru iylwenpeny'', previously only known as the "[[Alcoota]] ''Baru''",<ref name=YRS23/> while the year 2024 saw a reinterpretation of ''Ultrastenos'', concluding that it was synonymous with ''"Baru" huberi''.<ref name=YS24/>

== Species ==
{| class="wikitable"
|+
!Genus
!Species
!Age
!Location
!Notes
!Image
|-
|''[[Australosuchus]]''
|''A. clarkae''<ref name=WM91>{{cite journal|author1=Willis, P.M.A. |author2=Molnar, R.E. |name-list-style=amp |year=1991 |title=A new middle Tertiary crocodile from Lake Palankarinna, South Australia |journal=Records of the South Australian Museum |volume=25 |issue=1 |pages=39–55 |url=https://www.biodiversitylibrary.org/page/40724793#page/42/mode/1up }}</ref>
|Late Oligocene - Early Miocene
|{{flag|South Australia}}
|''Australosuchus'' is known from abundant remains; it was likely a semi-aquatic [[Generalist and specialist species|generalist]] and had a moderately broad and flattened skull. It is among the southern-most members of its family and has been hypothesized to have been much more cold resistant than its relatives, allowing it to thrive in areas where others could not.
|[[File:Australosuchus.jpg|frameless|Australosuchus]]
|-
|rowspan=3|''[[Baru]]''
|''B. darrowi''<ref name=WMM90>{{Cite journal|last1=Willis|first1=P.M.|last2=Murray|first2=P.|last3=Megirian|first3=D.|year=1990|title=''Baru darrowi'' gen. et sp. nov., a large, broad-snouted crocodyline (Eusuchia: Crocodylidae) from mid-Tertiary freshwater limestones in Northern Australia.|url=https://www.biodiversitylibrary.org/partpdf/74496|journal=Memoirs of the Queensland Museum|volume=29|issue=2|pages=521–540}}</ref>
|Middle Miocene
|{{flag|Queensland}}
{{flag|Northern Territory}}
|rowspan=3|Species of ''Baru'' are among the largest and most robust mekosuchines, bearing heavily built skulls with large and finely [[wiktionary:crenulate|crenulated]] teeth. Having reached lengths upwards of {{convert|4|m|abbr=on}}, they were the [[apex predator]]s of Miocene freshwater habitats. ''Baru'' is sometimes known as the "[[cleaver]]-headed crocodile".
|rowspan=3|[[File:Baru sp.jpg|frameless|Baru species]]
|-
|''B. iylwenpeny''<ref name=YRS23>{{cite journal|last1=Yates|first1=A.M.|last2=Ristevski|first2=J.|last3=Salisbury|first3=S.W.|year=2023|title=The last Baru (Crocodylia, Mekosuchinae): a new species of 'cleaver-headed crocodile' from central Australia and the turnover of crocodylians during the Late Miocene in Australia|journal=Papers in Palaeontology|volume=9|issue=5|doi=10.1002/spp2.1523|bibcode=2023PPal....9E1523Y }}</ref>
|Late Miocene
|{{flag|Northern Territory}}
|-
|''B. wickeni''<ref name=W97b>{{Cite journal|last1=Willis|first1=P.M.A.|year=1997|title=New crocodilians from the late Oligocene White Hunter Site, Riversleigh, northwestern Queensland|url=https://biostor.org/reference/105307|journal=Memoirs of the Queensland Museum|volume=41|pages=423–438|issn=0079-8835}}</ref>
|Late Oligocene
|{{flag|Queensland}}
{{flag|Northern Territory}}
|-
|''[[Kalthifrons]]''
|''K. aurivellensis''<ref name=Ka17>{{Cite journal|last1=Yates|first1=Adam M.|last2=Pledge|first2=Neville S.|date=2017-01-02|title=A Pliocene mekosuchine (Eusuchia: Crocodilia) from the Lake Eyre Basin of South Australia|journal=Journal of Vertebrate Paleontology|volume=37 |issue=1|article-number=e1244540 |doi=10.1080/02724634.2017.1244540 |s2cid=133338958|issn=0272-4634|jstor = 44866024|bibcode=2017JVPal..37E4540Y }}</ref>
|Pliocene
|{{flag|South Australia}}
|''Kalthifrons'' was a medium-sized mekosuchine found on the shores of Lake Palankarinna in South Australia. It is generally thought to have been a semi-aquatic generalist similar to modern crocodilians. It has been hypothesized that it might have either been outcompeted by the genus ''Crocodylus'' or that the latter filled the same niche following the extinction of ''Kalthifrons'' in the [[Lake Eyre Basin]].
|[[File:Kalthifrons skull reconstruction.jpg|frameless|Kalthifrons skull reconstruction]]
|-
|rowspan=4|''[[Kambara]]''
|''K. implexidens''<ref name=SW96>{{Cite journal|last1=Salisbury|first1=S. W.|last2=Willis|first2=P. M. A.|year=1996|title=A new crocodylian from the early Eocene of south-eastern Queensland and a preliminary investigation of the phylogenetic relationships of crocodyloids.|journal=Alcheringa|volume=20|issue=3 |pages=179–226|doi=10.1080/03115519608619189 |bibcode=1996Alch...20..179S }}</ref>
|Eocene
|{{flag|Queensland}}
|rowspan=4|All four known species of ''Kambara'' lived during the Eocene in what is now Queensland, with at least two of them possibly having coexisted. The different species chiefly differ in how their teeth occlude, with ''K. murgonensis'' possessing an [[overbite]] akin to an alligator whereas other species appear more similar to crocodiles in possessing interlocking teeth. Although fossil remains are numerous, most material of ''Kambara'' has never been properly [[Species description|described]].
|rowspan=4|[[File:Kambara skulls.png|frameless|Kambara skulls]]
|-
|''K. molnari''<ref name=H05>{{Cite journal|last1=Holt|first1= T. R.|last2=Salisbury|first2=S. W.|last3=Willis|first3=P.M.A.|year= 2005|title=A new species of mekosuchine crocodilian from the middle Palaeogene Rundle Formation, central Queensland.|url=https://www.researchgate.net/publication/43451834|journal=Memoirs of the Queensland Museum|volume=50|pages=207–218}}</ref>
|Eocene
|{{flag|Queensland}}
|-
|''K. murgonensis''<ref name=WMS93>{{Cite journal|last1=Willis|first1=P. M. A.|last2=Molnar|first2=R.E.|last3= Scanlon|first3=J.D.|year=1993|title=An early Eocene crocodilian from Murgon, southeastern Queensland.|url=https://www.academia.edu/56553132 |journal=Kaupia|issue=3|pages=27–33|via=[[Academia.edu]]}}</ref>
|Eocene
|{{flag|Queensland}}
|-
|''K. taraina''<ref name=B09>{{Cite journal|last1=Buchanan|first1= L.A.|year=2009|title=''Kambara taraina'' sp. nov. (Crocodylia, Crocodyloidea), a new Eocene mekosuchine from Queensland, Australia, and a revision of the genus|journal=Journal of Vertebrate Paleontology|volume=29|issue=2|pages=473–486|doi= 10.1671/039.029.0220|bibcode= 2009JVPal..29..473B|s2cid= 86254159}}</ref>
|Eocene
|{{flag|Queensland}}
|-
|rowspan=4|''[[Mekosuchus]]''
|''M. inexpectatus''<ref name=BB87>{{Cite journal|last1=Balouet|first1=J.|last2=Buffetaut|first2=E.|year=1987|title=''Mekosuchus inexpectatus'', n. Gen., n. Sp., crocodilien nouveau de l'Holocene de Nouvelle Calédonie|url=https://www.researchgate.net/publication/291823082|journal=Comptes Rendus de l'Académie des Sciences de Paris|volume=2|issue=304|pages=853–856}}</ref>
|Holocene
|{{flag|New Caledonia}}
|rowspan=4|Among the smallest mekosuchines, ''Mekosuchus'' was a long lived genus that first appeared during the Late Oligocene on mainland Australia and may have died out as recently as 3,000 years ago, if not more recently still. ''Mekosuchus'' is among the most enigmatic members of its group, with no strong consensus on what kind of lifestyle it had. A more terrestrial lifestyle is commonly suggested and sometimes the genus is likened to modern dwarf-crocodiles, which inhabit small rainforest streams.<ref name=R23b/>
|rowspan=4|[[File:Mekosuchus spp.png|frameless|Mekosuchus spp]]
|-
|''M. kalpokasi''<ref name=M02>{{cite journal |year=2002 |last1=Mead |first1=Jim I |last2=Steadman |first2=David W |last3=Bedford |first3=Stuart H |last4=Bell |first4=Christopher J |last5=Spriggs |first5=Matthew |title=New Extinct Mekosuchine Crocodile from Vanuatu, South Pacific |url=http://doc.rero.ch/record/16396/files/PAL_E3562.pdf|journal=Copeia |volume=2 |issue=3 |page=632 |doi=10.1643/0045-8511(2002)002[0632:NEMCFV]2.0.CO;2|s2cid=86065169 }}</ref>
|Holocene
|{{flag|Vanuatu}}
|-
|''M. sanderi<ref name=W01>{{Cite book|last1=Willis|first1=P. M. A.|year=2001|title= Crocodilian biology and evolution|chapter=New crocodilian material from the Miocene of Riversleigh (northwestern Queensland, Australia)|url=https://www.researchgate.net/publication/328369151|publisher=Surrey Beatty & Sons}}</ref>''
|Early Miocene
|{{flag|Queensland}}
|-
|''M. whitehunterensis''<ref name=W97b/>
|Late Oligocene - Early Miocene
|{{flag|Queensland}}
|-
|rowspan=2|''[[Paludirex]]''
|''P. gracilis''<ref name=WM97>{{Cite journal|last1=Willis|first1=P.M.A.|last2= Molnar|first2=R.E.|year=1997|title=A review of the Plio-Pleistocene crocodilian genus Pallimnarchus|url=https://ia800200.us.archive.org/34/items/biostor-85539/biostor-85539.pdf|journal=Proceedings of the Linnean Society of New South Wales|issue= 117|pages=223–242}}</ref>
|Late Pleistocene
|{{flag|Queensland}}
|rowspan=2|The genus ''Paludirex'' was established as a substitute for the poorly defined genus ''Pallimnarchus'' and is represented by two species. Among these, the larger ''P. vincenti'' is the single largest mekosuchine, reaching an estimated body length of around {{convert|5|m|abbr=on}}, although the smaller ''P. gracilis'' still reached lengths comparable to those of ''Baru''.
|rowspan=2|[[File:Paludirex species.jpg|frameless|Paludirex species]]
|-
|''P. vincenti''<ref name=R20>{{cite journal |last1=Ristevski |first1=J. |last2=Yates |first2=A.M. |last3=Price |first3=G.J. |last4=Molnar |first4=R.E. |author4-link=Ralph E. Molnar |last5=Weisbecker |first5=V. |last6=Salisbury |first6=S.W. |year=2020 |title=Australia's prehistoric 'swamp king': revision of the Plio-Pleistocene crocodylian genus ''Pallimnarchus'' de Vis, 1886 |journal=PeerJ |volume=8 |article-number=e10466 |doi=10.7717/peerj.10466|pmid=33391869 |pmc=7759136 |doi-access=free }}</ref>
|Pliocene - Pleistocene?
|{{flag|Queensland}}
|-
|rowspan=4|''[[Quinkana]]''
|''Q. fortirostrum''<ref name=M81>{{Cite journal|last=Molnar|first=R. E.|date=1981-10-31|title=Pleistocene ziphodont crocodilians of Queensland|journal=Records of the Australian Museum|volume=33|issue=19|pages=803–834|doi=10.3853/j.0067-1975.33.1981.198|issn=0067-1975|doi-access=free}}</ref>
|Pleistocene
|{{flag|Queensland}}
|rowspan=4|''Quinkana'' possessed an [[wiktionary:altirostris|altirostral]] skull and [[wiktionary:ziphodont|ziphodont]] dentition, leading scientists to compare it to sebecids and planocraniids, although none of them [[Convergent evolution|are closely related to each other]]. This has led to the hypothesis that ''Quinkana'' was a primarily terrestrial animal, although no postcranial material has been confidently assigned to the genus to confirm this.
|rowspan=4|[[File:Quinkana holotype specimens.jpg|frameless|Quinkana holotype specimens]]
|-
|''Q. babarra''<ref name= WM96>{{Cite journal|last1=Willis|first1=Paul M.A.|last2=Mackness|first2=Brian S.|date=1996|title=''Quinkana babarra'', a new species of ziphodont mekosuchine crocodile from the Early Pliocene Bluff Downs Local Fauna, Northern Australia with a revision of the genus|url=https://www.biodiversitylibrary.org/page/34936465|journal=Proceedings of the Linnean Society of New South Wales|volume=116|pages=143–151}}</ref>
|Early Pliocene
|{{flag|Queensland}}
|-
|''Q. meboldi''<ref name=W97b/>
|Late Oligocene
|{{flag|Queensland}}
|-
|''Q. timara''<ref name= M94>{{Cite journal|last=Megirian|first=Dirk|date=1994|title=A New Species of ''Quinkana'' Molnar (Eusuchia: Crocodylidae) from the Miocene Camfield Beds of Northern Australia|url=https://www.biodiversitylibrary.org/page/55849152|journal=The Beagle|volume=11|pages=145–166}}</ref>
|Middle Miocene
|{{flag|Northern Territory}}
|-
|''[[Trilophosuchus]]''
|''T. rackhami''<ref name=WPMA93>{{cite journal |last=Willis |first=P.M.A. |year=1993 |title=''Trilophosuchus rackhami'' gen. et sp. nov., a new crocodilian from the Early Miocene limestones of Riversleigh, northwestern Queensland |journal=Journal of Vertebrate Paleontology |volume=13 |issue=1 |pages=90–98 |doi=10.1080/02724634.1993.10011489|bibcode=1993JVPal..13...90W }}</ref>
|Oligocene - Miocene
|{{flag|Queensland}}
|Measuring an estimated {{convert|70-90|cm|abbr=on}} in length, ''Trilophosuchus'' is the smallest known mekosuchine. Described from a partial skull showing three distinct crests running down the skull table, ''Trilophosuchus'' shows signs of having been a more terrestrial animal that held its head higher than most modern taxa.
|[[File:Trilophosuchus.jpg|frameless|Trilophosuchus]]
|-
|''[[Ultrastenos]]''
|''U. huberi''<ref name=W97b/><ref name="Stein2016">{{cite journal |last1=Stein |first1=Michael |last2=Hand |first2=Suzanne J. |last3=Archer |first3=Michael |date=26 May 2016 |title=A new crocodile displaying extreme constriction of the mandible, from the late Oligocene of Riversleigh, Australia |journal=[[Journal of Vertebrate Paleontology]] |volume=36 |issue=5 |article-number=e1179041 |doi=10.1080/02724634.2016.1179041 |bibcode=2016JVPal..36E9041S |s2cid=88895724 |hdl=1959.4/unsworks_41114 |hdl-access=free }}</ref><ref name=YS24/>
|Late Oligocene
|{{flag|Queensland}}
|''Ultrastenos'' has a complex history that is split between two names. The snout was initially described under the name ''Baru huberi'', while the skull table was given the name ''Ultrastenos willisi'', only for researchers to later determine that both belonged to a single individual. Because of this, initial reconstructions depicted it as similar to a gharial, which was later proven to be incorrect.
|[[File:Ultrastenos 2024.jpg|frameless|Ultrastenos 2024]]
|-
|''[[Volia]]''
|''V. athollandersoni''<ref name=M02b>{{Cite journal|last1=Molnar|first1=R.E.|last2=Worthy|first2=T.|last3=Willis|first3=P.M.A.|year=2002|title=An extinct Pleistocene endemic mekosuchine crocodylian from Fiji.|url=https://www.researchgate.net/publication/233316814|journal=Journal of Vertebrate Paleontology|volume=22|issue=3|pages=612–628|doi=10.1671/0272-4634(2002)022[0612:AEPEMC]2.0.CO;2|s2cid=85592048 }}</ref>
|Pleistocene
|{{flag|Fiji}}
|''Volia'' was a medium-sized [[Island ecology|insular]] mekosuchine endemic to the island of Fiji, where it lived during the Pleistocene. At {{convert|2-3|m|abbr=on}} in length, it was the largest predator on the island and likely fed on [[flightless bird]]s and [[Lapitiguana|giant iguanas]].
|[[File:Volia.jpg|frameless|Volia]]
|-
|}

Though sometimes included within Mekosuchinae,<ref name=W97b/><ref name="Stein2016"/> the Miocene taxon ''[[Harpacochampsa]]'' is regarded as a type of [[Gavialoidea|gavialoid]] in recent research.<ref name="Ka17" /><ref name="R23b" /><ref name=RM21/><ref name=LY18/>

===Unnamed forms===
[[File:Darling Downs taxon.jpg|thumb|The as of yet unnamed "Darling Downs taxon".]]
In addition to the many named genera and species, scientists also recognize a plethora of distinct taxa that [[Undescribed taxon|have not been scientifically described]] or named yet. Among these is the so-called "[[Darling Downs]] taxon", which is represented by multiple bone fragments that bear some resemblance to species of the genus ''Paludirex'' while also being visibly distinct from both named species. While too fragmentary to conclusively assign to the genus or erect as a new species, the material has been tentatively regarded as a third species of ''Paludirex'', with the possibility that it might be a different genus altogether.<ref name=R20/> Another example would be the "[[Bullock Creek (Northern Territory)|Bullock Creek]] taxon", a small mekosuchine long known to share affinities with ''Ultrastenos'' and which likely belongs to the genus, but as of yet unnamed.<ref name=YS24/>

Unnamed species are also known for the genus ''Quinkana'', notably in the form of the [[Ongeva Local Fauna|Ongeva]] ''Quinkana'' from Alcoota.<ref name=W97b/> The "[[Floraville, New South Wales|Floraville]] taxon", meanwhile, may represent a separate genus of ziphodont mekosuchine rather than another ''Quinkana'' species.<ref name=R23b/> Ziphodont crocodilian teeth have also been recovered from Australia's [[Mount Etna Caves National Park]].<ref name="Ho05">{{Cite journal |last1=Hocknull |first1=S.A. |year=2005 |title=Ecological succession during the late Cainozoic of central eastern Queensland: extinction of a diverse rainforest community. |url=https://www.biodiversitylibrary.org/part/264041 |journal=Memoirs of the Queensland Museum |volume=51 |issue=1 |pages=39–122}}</ref><ref name="SPK13">{{Cite journal |last1=Sobbe |first1=Ian H. |last2=Price |first2=Gilbert J. |last3=Knezour |first3=Robert A. |date=2013 |title=A ziphodont crocodile from the late Pleistocene King Creek catchment, Darling Downs, Queensland |url=https://www.researchgate.net/publication/256440898 |journal=[[Memoirs of the Queensland Museum]] |volume=52 |issue=2 |pages=601–606|doi=10.17082/j.2204-1478.56.2.2013-14 }}</ref>

Remains of a ziphodont crocodilian have been known from the Pliocene [[Otibanda Formation]] of [[Papua New Guinea]] since 1967,<ref name=M81/> but were initially referred to [[Sebecosuchia]] before the discovery of ziphodont mekosuchines. Given that they were not figured nor described in detail, the affinities of these teeth remained largely mysterious in the following 50 years.<ref name=R23b/> This changed in late 2024, when the teeth were described in greater detail by Ristevski, Molnar and Yates. The study identifies the remains as ?Mekosuchinae gen. et sp. indet., reasoning that the geography and age would be very unusual for any of the other Cenozoic ziphodont crocodylomorph, yet its morphologically not possible to distinguish it from sebecosuchians or planocraniids. Similarly, it's not possible to distinguish it from species of the genus ''Quinkana'' until a better understanding of the variation between ziphodont crocodilian teeth is achieved.<ref name=RMY24>{{Cite journal|last1=Ristevski|first1=J.|last2=Molnar|first2=R.E.|last3= Yates| first3=A.M.|year=2024|title= Reassessment of isolated reptilian teeth confirms the presence of ziphodont crocodylians during the Pliocene of New Guinea|journal=Historical Biology|pages=1–24 |doi=10.1080/08912963.2024.2429585}}</ref>

Another geographically significant putative mekosuchine is the "[[Bannockburn Formation]] taxon", a crocodilian that lived in [[New Zealand]] during the Early Miocene. While the material is too fragmentary to be tested for mekosuchine affinities, field work near [[St Bathans fauna|St. Bathans]] has recovered more material that could help resolve the matter. Additionally, these finds also seem to suggest that at least two different crocodilians inhabited New Zealand during this time period.<ref name="R23b" /><ref name=MP97>{{Cite journal|last1=Molnar|first1=R.E.|last2=Pole|first2=M.|year=1997|title=A Miocene crocodilian from New Zealand|url=https://www.academia.edu/751077|journal=Alcheringa|volume=21|issue=1|pages=65–70|doi=10.1080/03115519708619185 |bibcode=1997Alch...21...65M |via=[[Academia.edu]]}}</ref>

Much like the "Bannockburn Formation taxon", the "[[Runcorn, Queensland|Runcorn]] taxon" (named after a [[suburb]] of [[Brisbane]]) is too fragmentary to be conclusively assigned to Mekosuchinae, but is often speculated to have been a part of the group regardless, with Paul Willis even suggesting it may have been a species of ''Kambara''.<ref name="R23b" /><ref name=WM91b>{{Cite journal|last1=Willis|first1=P. M. A.|last2=Molnar|first2=R. E.|year=1991|title=A longirostrine crocodile from the Early Tertiary of southeastern Queensland|journal=Alcheringa: An Australasian Journal of Palaeontology|volume=15|issue=3|pages=229–233|doi=10.1080/03115519108619019|bibcode=1991Alch...15..229W }}</ref>

==Description==
{{multiple image
| perrow            = 2/1
| total_width       = 250
| image1            = Trilophosuchus skull reconstructed.png
| image2            = Australosuchus skull.png
| image3            = Baru sp alcoota.jpg
| footer            = Mekosuchines were a diverse group, featuring animals with short, boxy skulls; platyrostral generalists and robust macropredators.
| align             = left
}}

===Skull shape===
One of the most noticeable traits of mekosuchines is the wide range of skull shapes found across the family. At their simplest mekosuchines greatly resemble modern crocodiles, with taxa such as ''Kambara'',<ref name=WMS93/><ref name=SW96/> ''Ultrastenos'',<ref name=YS24/> and ''Australosuchus'' having triangular platyrostral skulls, meaning that they are flattened, with both the nostrils and eyes mostly facing upwards.<ref name=WM91/> The specifics of this [[morphotype]] differ among taxa, as seen between the [[sympatry|contemporary]] ''Kambara implexidens'' with its relatively narrow snout and the much more wide-snouted ''K. murgonensis''.<ref name=WMS93/><ref name="SW96" /> As with many modern crocodilians, the skulls feature various degrees of festooning, which describes the patterns of constriction that give the rostrum a somewhat [[wiktionary:sinuous|sinuous]] outline. Especially prominent is a notch formed just behind the [[premaxilla]]e that received the fourth tooth of the lower jaw when the jaws were closed. In this regard, ''Australosuchus'' stands out in having this fourth dentary tooth almost entirely enclosed, with the notch being more accurately described as a semi-enclosed pit.<ref name=WM91/> Another deviation from the platyrostral morphotype is seen in ''Paludirex'', which, although still platyrostral, has a much deeper and more robust skull shape with a rostrum that is proportionally much wider than that of other platyrostral mekosuchines.<ref name=R20/>

Members of the genus ''Baru'' combine the wedge-shaped triangular skull and strong festooning seen in many generalist forms with a more altirostral skull morphology, making their heads much deeper than those of other mekosuchines.<ref name=WMM90/> The festooning is especially strong in ''Baru'' and the teeth are described as enlarged and laterally compressed.<ref name="W97" /><ref name=Y17>{{Cite journal|last1=Yates|first1=A.M.|year=2017|title=The biochronology and palaeobiogeography of Baru (Crocodylia: Mekosuchinae) based on new specimens from the Northern Territory and Queensland, Australia.|journal=PeerJ|volume=5|article-number=e3458 |doi=10.7717/peerj.3458 |doi-access=free |pmid=28649471 |pmc=5482264 }}</ref> The teeth of two of the species, ''B. darrowi'' and ''B. iylwenpeny'', bear fine [[serration]]s along the cutting edges of the teeth. This led some early publications to refer to them as [[wikt:ziphodont|ziphodont]], although later papers prefer the term "[[wiktionary:crenulate|crenulated]]" to distinguish them from truly ziphodont teeth.<ref name=YRS23/><ref name=Y17/>

True ziphodonty, as well as an even more developed altirostral skull, are hallmarks of the genus ''Quinkana''. Like in ''Baru'', the skull of ''Quinkana'' is distinctly [[trapezoid]] in [[Cross section (geometry)|cross-section]] and noticeably deeper than those of more generalized mekosuchines and modern crocodiles. The skull of ''Quinkana'' is generally compared to those of [[sebecosuchia]]ns and [[Planocraniidae|planocraniids]],<ref name= M77/><ref name=M81/> with that of ''Q. fortirostrum'' distinctly broader and resembling the former and that of ''Q. timara'' being closer to the latter.<ref name=M81/><ref name="M94" /> Festooning is almost nonexistent in ''Q. fortirostrum'', with the lower margin of the rostrum almost straight, save for a notch behind the premaxilla. The teeth are blade-like, laterally compressed and ziphodont in most species, the [[wiktionary:carina#English|carinae]] being adorned by a series of prominent serrations.<ref name=M81/> Unlike the crenulations seen in ''Baru'', the denticles that form the serrations on ''Quinkana'' teeth are separated by distinct [[wiktionary:sulcus|sulci]].<ref name=YRS23/> The number of denticles differs, with ''Q. timara'' having finer serrations due to having more denticles relative to ''Q. fortirostrum'', while ''Q. meboldi'' lacks them altogether.<ref name="R23b" /><ref name=SPK13/>

The fourth major skull morphotype seen in mekosuchines is displayed by the dwarf taxa ''Trilophosuchus'' and ''Mekosuchus'' and also falls into the category of altirostry, while at the same time being shortened ([[brachycephaly|brachycephalic]]). These taxa had boxy skulls with large eyes that bear some resemblance to [[dwarf caiman]]s and [[dwarf crocodile]]s, as well as extinct animals like ''[[Theriosuchus]]'', ''[[Protosuchus]]'' and various [[notosuchia]]ns.<ref name=WPMA93/><ref name=W97/><ref name="Br01" /> No teeth are known from ''Trilophosuchus'',<ref name=WPMA93/> while the teeth of ''Mekosuchus'' seem to have had different morphologies depending on the species. The continental ''M. whitehunterensis'' and ''M. sanderi'' display blade-like teeth,<ref name=W01/><ref name=M02/> while at least the posterior teeth of the island species ''M. inexpectatus'' were blunt and rounded.<ref name=B91/><ref name=BB87/><ref name=M02/><ref name="H07">{{Cite conference |last1=Holt |first1=T.R. |last2=Salisbury |first2=S.W. |last3=Worthy |first3=T. |last4=Sand |first4=C. |last5=Anderson |first5=A. |year=2007 |title=New material of Mekosuchus inexpectatus (Crocodylia: Mekosuchinae) from the Quaternary of New Caledonia |url=https://www.researchgate.net/publication/43494531 |conference=11th Conference on Australian Vertebrate Evolution, Palaeontology and Systematics |location=Melbourne, Australia}}</ref>

===Size===
Mekosuchines come in a wide range of sizes, with the smallest known genus ''Trilophosuchus'' measuring an estimated {{convert|70–90|cm|abbr=on}} long.<ref name=R23a/> ''Trilophosuchus'' is one of several small-bodied taxa placed in a clade of dwarf and insular mekosuchines, with other notable dwarf taxa including ''Mekosuchus whitehunterensis'', estimated to reach lengths around {{convert|60|cm|abbr=on}},<ref name=S14/><ref name=SAH15/> ''Ultrastenos'', which possibly reached a length of around {{convert|1.5|m|abbr=on}},<ref name=W02/> and ''M. inexpectatus'', which has been estimated to have grown to lengths of around {{convert|1|m|abbr=on}} by Holt and up to {{convert|2|m|abbr=on}} by Balouet.<ref name=B91/><ref name="H07" />

Species of ''Quinkana'' have been estimated between {{convert|1.5|m|abbr=on}} for ''Q. meboldi'' and {{convert|3|m|abbr=on}} for ''Q. fortirostrum'',<ref name="SPK13" /><ref name="W02" /><ref name=F90>{{Cite journal|last1=Flannery|first1=T. F.|year=1990|title=Pleistocene faunal loss: implications of the aftershock for Australia's past and future.|journal= Archaeology in Oceania|volume=25|issue=2|pages= 45–55|doi=10.1002/j.1834-4453.1990.tb00232.x}}</ref> pushing it into the range of the medium-sized members of the family. Some larger reports exist, but these concern remains that are poorly understood and fragmentary.<ref name="M04" /><ref name=S95>{{Cite conference|last1=Salisbury|first1=S. W.|last2=Willis|first2=P.M.A.|last3=Scanlon|first3=J.D.|last4=Mackness|first4=B.S.|year=1995|title=Plio-Pleistocene gigantism in Quinkana (Crocodyloidea; Mekosuchinae)|conference=Linnean Society of New South Wales Symposium on the Quaternary|volume=10}}</ref> Other mekosuchines in this range include ''Kalthifrons'',<ref name=Ka17/> ''Australosuchus'' and ''Kambara'', with the latter reaching between {{convert|2.5-4|m|abbr=on}} depending on the species.<ref name="WM91" /><ref name="SW96" /><ref name=H05/>

The largest well understood mekosuchines belong to the genera ''Baru'' and ''Paludirex'', reaching lengths of {{convert|4|m|abbr=on}}<ref name=W97/><ref name=W02/> and {{convert|5|m|abbr=on}} respectively.<ref name="M04" /><ref name=Crikey>{{Cite web|title=Crikey! Massive prehistoric croc emerges from South East Queensland|url=https://www.sciencedaily.com/releases/2020/12/201221101144.htm|access-date=2021-01-09|website=ScienceDaily|language=en}}</ref><ref name=W13>{{Cite journal|last1=Wroe|first1=S. |last2=Field|first2=J.H.|last3=Archer|first3=M. |last4=Grayson|first4=D.K. |last5=Price|first5=G.J.| last6=Louys|first6=J. |last7=Faith|first7=T.|last8=Webb|first8=G.E.|last9=Davidson|first9=I. |last10=Mooney|first10=S.D.|year=2013|title=Climate change frames debate over the extinction of megafauna in Sahul (Pleistocene Australia-New Guinea).|journal=Proceedings of the National Academy of Sciences|volume=110|issue=22|pages=8777–8781|doi=10.1073/pnas.1302698110 |pmid=23650401 |bibcode=2013PNAS..110.8777W |doi-access=free |pmc=3670326}}</ref>

==Phylogeny==
===Internal relationships===
Mekosuchinae is [[cladistic]]ally defined as a [[node-based taxon]] composed of the [[last common ancestor]] of ''[[Kambara implexidens]]'', ''[[Mekosuchus inexpectatus]]'', and all of its descendants. Beyond this definition, which necessitates the inclusion of ''Kambara'' and ''Mekosuchus'' in the clade, various different interpretations of the members of the group and their internal relationships exist. These interpretations differ in a multitude of ways, but also share certain topologies. For instance, taxa such as ''Kambara'' and ''Australosuchus'' are typically regarded as being basal offshoots of the family, sometimes joined by the much younger genus ''Kalthifrons''. Ristevski and colleagues recovered ''Kalthifrons'' as the first mekosuchine to split from the clade, followed by ''Kambara'' and ''Australosuchus'', in 2023.<ref name=R23b/> This is contrasted by a 2023 publication by Yates, Ristevski & Salisbury, who found ''Kambara'' and ''Australosuchus'' to form their own small clade at the base of the group with ''Kalthifrons'' diverging at a slightly later time.<ref name=YRS23/> Meanwhile, a publication by Lee & Yates in 2018 recovered ''Australosuchus'' as the basalmost mekosuchine, followed by ''Kambara'' and finding ''Kalthifrons'' in a much more derived position among the members of mekosuchinae.<ref name=LY18>{{cite journal | author=Michael S. Y. Lee |author2=Adam M. Yates |date=27 June 2018 |title=Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil |journal=[[Proceedings of the Royal Society B]] |volume=285 |issue=1881 |doi=10.1098/rspb.2018.1071 |pmid=30051855 |pmc=6030529 |doi-access=free}}</ref>

Modern phylogenies commonly see more derived members of the family split among two branches that diverge from another after taxa like ''Kambara'' and ''Australosuchus'' do. Ristevski ''et al.'', 2023, sees the family split into two clades: one containing the large bodied forms ''Baru'', ''Paludirex'' and ''Quinkana''; and one clade of insular and dwarf taxa, which features ''Ultrastenos'', ''Trilophosuchus'', ''Volia'' and ''Mekosuchus''.<ref name=R23b/> Lee and Yates also recovered this split in 2018, although the makeup of the clades differs slightly. In their study, ''Baru'' still clades with ''Paludirex'' (here still ''Pallimnarchus''), but in place of ''Quinkana'' the clade instead includes ''Kalthifrons''. The other clade is likewise similar to what has been recovered by later studies, featuring ''Ultrastenos'' (then known as ''"Baru" huberi'' and clading with the undescribed Bullock Creek taxon), ''Volia'', ''Mekosuchus'', ''Trilophosuchus'' and ''Quinkana''.<ref name=LY18/> Yates, Ristevski and Salisbury did not recover this distinct branching of clades in their 2023 study, however, their phylogeny also did not include several taxa present in the other studies.<ref name=YRS23/>

The phylogenies mentioned above can be seen here:
{{col-begin|width=70%}}
{{col-3}}
Lee & Yates, 2018
{{clade| style=font-size:85%;line-height:85%
|1={{clade
       |label1='''Mekosuchinae'''
       |1={{clade
        |1=''[[Australosuchus]]''{{extinct}}
        |2={{clade
         |1={{clade
          |1=''[[Kambara taraina]]''{{extinct}}
          |2=''[[Kambara implexidens]]''{{extinct}} }}
         |2={{clade
          |1=''[[Kambara murgonensis]]''{{extinct}}
          |2={{clade
           |1={{clade
            |1={{clade
             |1=''[[Kalthifrons]]''{{extinct}}
             |2=''[[Pallimnarchus]]''{{extinct}} }}
            |2={{clade
             |1=''[[Baru wickeni]]''{{extinct}}
             |2={{clade
              |1=''[[Baru darrowi]]''{{extinct}}
              |2=''[[Baru]]'' Alcoota{{extinct}} }} }} }}
           |2={{clade
            |1={{clade
             |1=Bullock Creek taxon{{extinct}}
             |2=''[["Baru" huberi]]''{{extinct}} }}
            |2={{clade
             |1=''[[Volia]]''{{extinct}}
             |2={{clade
              |1={{clade
               |1=''[[Mekosuchus inexpectatus]]''{{extinct}}
               |2={{clade
                |1=''[[Mekosuchus whitehunterensis]]''{{extinct}}
                |2=''[[Mekosuchus sanderi]]''{{extinct}}
              }}}}
              |2={{clade
               |1=''[[Trilophosuchus]]''{{extinct}}
               |2={{clade
                |1=''[[Quinkana meboldi]]''{{extinct}} 
                |2={{clade
                 |1=''[[Quinkana timara]]''{{extinct}} 
                 |2=''[[Quinkana fortirostrum]]''{{extinct}} 
                }} }} }} }} }} }} }} }} }} }}
       |2=[[Longirostres]]
}} }}
{{col-3}}
Yates, Ristevski & Salisbury, 2023
{{clade| style=font-size:85%;line-height:85%
|1={{clade
 |label1=[[Crocodyloidea]]
 |1={{clade
  |1=''[["Crocodylus" megarhinus]]''{{extinct}}
  |2={{clade
   |label1='''Mekosuchinae'''
   |1={{clade
    |1={{clade
     |1=''[[Australosuchus]]''{{extinct}}
     |2={{clade
      |1=''[[Kambara implexidens]]''{{extinct}}
      |2=''[[Kambara taraina]]''{{extinct}}
      |3=''[[Kambara murgonensis]]''{{extinct}}  
    }}}}
    |2={{clade
     |1=''[[Kalthifrons]]''{{extinct}}
     |2={{clade
      |1=''[[Quinkana timara]]''{{extinct}}
      |2={{clade
       |1={{clade
        |1=''[[Mekosuchus whitehunterensis]]''{{extinct}}
        |2=''[[Mekosuchus sanderi]]''{{extinct}}
       }}
       |2={{clade
        |1=''[[Paludirex vincenti]]''{{extinct}}
        |2={{clade
         |1=''[[Baru|Baru iylwenpeny]]''{{extinct}}
         |2={{clade
          |1=''[[Baru darrowi]]''{{extinct}}
          |2=''[[Baru wickeni]]''{{extinct}}
}}}}}}}}}}}}}}
   |2=[[Crocodylidae]]
}}}}}}}}
{{col-3}}
Ristevski ''et al.'' (modified by Yates & Stein, 2024)<ref name=YS24>{{cite journal|last1=Yates|first1=A.M.|last2=Stein|first2=M.|year=2024|title=A reinterpretation and taxonomic revision of Ultrastenos willisi Stein, Hand and Archer, 2016, a short-snouted mekosuchine crocodylian from the Oligocene of northern Australia.|url=https://palaeo-electronica.org/content/2024/5183-ultrastenos-revised|journal=Palaeontologia Electronica|volume=27|issue=1|doi=10.26879/1355|doi-access=free}}</ref>
{{clade| style=font-size:85%;line-height:85%
|1={{clade
 |label1=[[Crocodyloidea]]
 |1={{clade
  |1=''[["Crocodylus" megarhinus]]''{{extinct}}
  |2={{clade
   |label1='''Mekosuchinae'''
   |1={{clade
    |1=''[[Kalthifrons aurivellensis]]''{{extinct}}
    |2={{clade
     |1={{clade
      |1=''[[Kambara implexidens]]''{{extinct}}
      |2={{clade
       |1=''[[Kambara taraina]]''{{extinct}}
       |2=''[[Kambara murgonensis]]''{{extinct}}
     }}}}
     |2={{clade
      |1=''[[Australosuchus]]''{{extinct}}
      |2={{clade
       |1={{clade
        |1=''[[Ultrastenos]]''{{extinct}}
        |2={{clade
         |1=''[[Trilophosuchus]]''{{extinct}}
         |2={{clade
          |1=''[[Volia]]''{{extinct}}
          |2={{clade
           |1=''[[Mekosuchus whitehunterensis]]''{{extinct}}
           |2={{clade
            |1=''[[Mekosuchus sanderi]]''{{extinct}}
            |2=''[[Mekosuchus inexpectatus]]''{{extinct}}
       }}}}}}}}}}
       |2={{clade
        |1={{clade
         |1=''[[Paludirex gracilis]]''{{extinct}}
         |2=''[[Paludirex vincenti]]''{{extinct}}
         }}
        |2={{clade
         |1={{clade
          |1=''[[Baru wickeni]]''{{extinct}}
          |2=''[[Baru darrowi]]''{{extinct}}
         }}
         |2={{clade
          |1=''[[Quinkana meboldi]]''{{extinct}} 
          |2={{clade
           |1=''[[Quinkana timara]]''{{extinct}} 
           |2=''[[Quinkana fortirostrum]]''{{extinct}} 
   }}}}}}}}}}}}}}}}
   |2=[[Crocodylidae]]
}}}}}}}}
{{col-end}}

A stark contrast to these comparably similar phylogenies can be found in a 2021 study by Jonathan Rio & Philip D. Mannion. The most notable differences from the above phylogenies are the placements of ''Australosuchus'' and ''Quinkana'', neither of which were recovered as mekosuchines in this study. ''Australosuchus'' was placed just outside of [[Crocodylidae]] and ''Quinkana'' was recovered as a proper [[Crocodylinae|crocodyline]], sister to ''"Crocodylus" megarhinus''. In exchange, the Chinese taxon ''[[Asiatosuchus|"Asiatosuchus" nanlingensis]]'' was placed within an offshoot of mekosuchinae alongside a [[paraphyletic]] ''Kambara''. Other elements are however more similar to the studies of Yates, Ristevski and colleagues. ''Kambara'' remains a basal mekosuchine and a distinct dwarf clade can be observed, formed in this case by ''Mekosuchus'', ''Trilophosuchus'' and ''Ultrastenos''. Notably, this study predates the 2024 reinterpretation of ''Ultrastenos'' and thus also includes ''"Baru" huberi'' as a separate taxon, although both fall within the dwarf clade.<ref name=RM21>{{cite journal |last1=Rio |first1=Jonathan P. |last2=Mannion |first2=Philip D. |date=6 September 2021 |title=Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem |journal=[[PeerJ]] |volume=9 |article-number=e12094 |doi=10.7717/peerj.12094 |pmid=34567843 |pmc=8428266 |doi-access=free}}</ref>

{{clade| style=font-size:85%;line-height:85%
|1={{clade
 |label1='''Mekosuchinae'''
 |1={{clade
  |1={{clade
   |1=''[[Kambara implexidens]]''{{extinct}}
   |2={{clade
    |1=''[[Kambara taraina]]''{{extinct}}
    |2={{clade
     |1=''[[Kambara murgonensis]]''{{extinct}}
     |2=''[[Asiatosuchus|"Asiatosuchus" nanlingensis]]''{{extinct}}
  }}}}}}
  |2={{clade
   |1={{clade
    |1=''[[Baru darrowi]]''{{extinct}}
    |2=''[[Baru wickeni]]''{{extinct}}
   }}
   |2={{clade
    |1=''[["Baru" huberi]]''{{extinct}}
    |2={{clade
     |1=''[[Trilophosuchus]]''{{extinct}}
     |2={{clade
      |1=''[[Ultrastenos]]''{{extinct}}
      |2=''[[Mekosuchus whitehunterensis]]''{{extinct}}
      |3=''[[Mekosuchus sanderi]]''{{extinct}}
      |4=''[[Mekosuchus inexpectatus]]''{{extinct}}
 }}}}}}}}}}
 |2={{clade
  |1=''[[Australosuchus]]''{{extinct}}
  |label2=Crocodylidae
  |2={{clade
   |1=[[Osteolaeminae]]
   |label2=Crocodylinae
   |2={{clade
    |1={{clade
     |1=''[[Quinkana]]''{{extinct}}
     |2=''[["Crocodylus" megarhinus]]''{{extinct}}
    }}
    |2=''[[Crocodylus]]''
}}}}}}}}}}

===Orientalosuchina===
[[File:Orientalosuchus skulls coll - Massonne et al 2019.png|thumb|right|It is possible that the Cretaceous and Paleogene members of Orientalosuchina were relatives of the mekosuchines.]]
In addition to the more standard topology recovered by Ristevski and colleagues, they also produced two phylogenetic trees that represent the two most novel interpretations of the group. These trees prominently feature the clade Orientalosuchina, crocodilians that lived during the Cretaceous and Palgeogene in Asia, as being deeply nested within Mekosuchinae. In both trees Mekosuchinae is divided into two clades, a feature they share with other analyses. The more traditional of these clades includes various medium- to large-sized taxa from continental Australia, namely ''Kalthifrons'', ''Quinkana'', ''Baru'' and ''Paludirex'', not dissimilar to the other trees recovered by Ristevski ''et al.''. Meanwhile, the other clade includes Orientalosuchina and small-bodied as well as insular taxa, in other words: ''Ultrastenos'', ''Trilophosuchus'', ''Volia'' and ''Mekosuchus''.<ref name=R23b/>

Within this topology, orientalosuchins are mostly grouped together to form their own [[monophyletic]] clade that acts as the sister-group to the small-bodied mekosuchines. This clade includes the genera ''[[Krabisuchus]]'', ''[[Orientalosuchus]]'', ''[[Jiangxisuchus]]'' and ''[[Eoalligator]]'', but not ''[[Dongnanosuchus]]'', which is closer to the traditional mekosuchine taxa. ''[[Protoalligator]]'' also wasn't part of the clade, but unlike ''Dongnanosuchus'' this is related to the animal being recovered as a basal [[eusuchia]]n instead of a mekosuchine. Another notable divergence from the traditional interpretation of Mekosuchinae concerns ''Australosuchus'' and ''Kambara'', which are both recovered as non-mekosuchines. In addition to changing the internal composition of the clade, the phylogenetic trees recovering Orientalosuchina within Mekosuchinae also shuffle how the group relates to other crocodilians. While mekosuchines as a whole are more distantly related to true crocodiles in these trees, ''Australosuchus'' and ''Kambara'' remain closely allied to [[Crocodyloidea]]. Specifically, ''Australosuchus'' is recovered as the basalmost crocodyloid in both analyses, while ''Kambara'' was recovered as the direct sister taxon to [[Crocodylidae]].<ref name="R23b" />

{{clade| style=font-size:85%;line-height:85%
|label1='''Mekosuchinae'''
|1={{clade
 |1={{clade
  |1=''[[Kalthifrons]]''
  |2={{clade
   |1={{clade
    |1=''[[Quinkana meboldi]]''
    |2={{clade
     |1=''[[Quinkana fortirostrum]]''
     |2=''[[Quinkana timara]]''
   }}}}
   |2={{clade
    |1={{clade
     |1=''[[Paludirex gracilis]]''
     |2=''[[Paludirex vincenti]]''
    }}
    |2={{clade
     |1=''[[Baru wickeni]]''
     |2=''[[Baru darrowi]]''
 }}}}}}}}
 |2={{clade
  |label1=Orientalosuchina
  |1={{clade
   |1=''[[Krabisuchus]]''
   |2={{clade
    |1=''[[Orientalosuchus]]''
    |2={{clade
     |1=''[[Jiangxisuchus]]''
     |2=''[[Eoalligator]]''
  }}}}}}
  |2={{clade
   |1=''[[Dongnanosuchus]]''
   |2={{clade
    |1=''[["Baru" huberi]]''
    |2={{clade
     |1=''[[Volia]]''
     |2=''[[Trilophosuchus]]''
     |3={{clade
      |1=''[[Mekosuchus sanderi]]''
      |2=''[[Mekosuchus whitehunterensis]]''
      |3=''[[Mekosuchus inexpectatus]]''
}}}}}}}}}}}}}}

However, there is little evidence that actually supports this grouping. Five possible [[synapomorphies]] were identified in the trees that feature Orientalosuchina as members of Mekosuchinae, although none of them are exclusive to these groups nor identified in all included members. Various other morphological features are shared between certain mekosuchines and orientalosuchins as well, but these are also either inconsistently present or widespread amongst crocodilians, especially among [[alligatoroids]]. Additionally, the remainder of the eight analyses all recovered a more traditional Mekosuchinae, while members of Orientalosuchina claded with alligatoroids. Ristevski and colleagues conclude that the evidence to support this hypothesis is weak, both phylogenetically and morphologically, but should nonetheless be explored in greater detail.<ref name=R23b/>

===External relationships===
{{multiple image
| perrow            = 1/1
| total_width       = 250
| image1            = NileCrocodile--Etiopia-Omo-River-Valley-02.jpg
| image2            = The Indian Gharial.jpg
| footer            = Mekosuchines are either close relatives of true crocodiles or basal to true crocodiles and gharials.
| align             = right
}}
The relationships between mekosuchines and other groups of crocodilians is another matter that has seen repeated shifts across time. When Mekosuchidae was established in 1987 for ''Mekosuchus'', the then monotypic family was placed within [[Eusuchia]].<ref name=BB87/> However, around that time crocodile phylogenetics were still poorly studied and Eusuchia was considered a subgroup of Crocodylia, unlike today. By 1993, when Mekosuchinae was coined to include all other Australian Cenozoic crocodilians known at the time, the clade was placed in the family [[Crocodylidae]] and regarded as a mere [[subfamily]], a view that remained prominent in literature in subsequent years.<ref name=WMS93/>

Today however this view is no longer supported, with modern phylogenetic analysis generally agreeing that the clade does not represent a subfamily of crocodylids, but rather a more basal clade. While it is not exactly agreed upon where the group splits off, two main hypotheses exist. In their 2018 study, which incorporates [[morphology (biology)|morphological]], molecular ([[DNA sequencing]]), and [[stratigraphic]] ([[fossil]] age) data, Lee and Yates recover mekosuchines as the sister group to [[Longirostres]], which is formed by modern gharials (and false gharials) together with true crocodiles.<ref name=LY18/> Similar results were yielded by two phylogenetic trees recovered by Ristevski and colleagues in 2023, with the better resolved of the two suggesting that mekosuchines (including Orientalosuchina) split from other crocodilians at some point after [[Planocraniidae|planocraniids]] but before the split between crocodyloids and gavialoids.<ref name=R23b/>

The more widely accepted hypothesis is the notion that mekosuchines, while not members of the Crocodylidae itself, are still crocodyloids. Following this hypothesis, which was also recovered by Ristevski ''et al.'' in 2023, they are nested deep within Longirostres as the immediate sister group to crocodylids, with the African ''[["Crocodylus" megarhinus]]'' as the sister taxon to the clade formed by crocodylids and mekosuchines.<ref name=R23b/> The same topology was previously reported by Rio & Mannion in 2021,<ref name=RM21/> and was later repeated in a 2023 publication by Yates, Ristevski and Salisbury.<ref name=YRS23/>

{|- valign="top"
| align="left" width="50%" |
{{clade| style=font-size:85%;line-height:85%
|label1=Crocodylia
|1={{clade
 |1=[[Alligatoroidea]]
 |2={{clade
  |1=[[Planocraniidae]]{{extinct}}
  |2={{clade
   |1={{clade
    |1=''[[Asiatosuchus germanicus]]''{{extinct}}
    |2='''Mekosuchinae'''{{extinct}}
   }}
   |2={{clade
    |1=''[[Prodiplocynodon]]''{{extinct}}
    |2={{clade
     |1={{clade
      |1=''[["Crocodylus" affinis]]''{{extinct}}
      |2=''[[Crocodylus depressifrons|"Crocodylus" depressifrons]]''{{extinct}}
     }}
     |2={{clade
      |1=''[["Crocodylus" acer]]''{{extinct}}
      |2=''[[Brachyuranochampsa]]''{{extinct}}
     }}
     |label3=Longirostres
     |3={{clade
      |1=[[Gavialoidea]]
      |2=[[Crocodyloidea]]
}}}}}}}}}}}}}}
| align="left" width="50%"|
{{clade| style=font-size:85%;line-height:85%
|label1=Crocodylia
|1={{clade
 |1={{clade
  |1=''[[Borealosuchus|Borealosuchus spp.]]''{{extinct}}
  |2=[[Alligatoroidea]]
 }}
 |2={{clade
  |1=[[Planocraniidae]]{{extinct}}
  |2={{clade
   |1=''[[Prodiplocynodon]]''{{extinct}}
   |2={{clade
    |1={{clade
     |1=''[["Crocodylus" affinis]]''{{extinct}}
     |2=''[[Crocodylus depressifrons|"Crocodylus" depressifrons]]''{{extinct}}
    }}
    |2={{clade
     |1=''[[Asiatosuchus germanicus]]''{{extinct}}
     |2={{clade
      |1={{clade
       |1=''[["Crocodylus" acer]]''{{extinct}}
       |2=''[[Brachyuranochampsa]]''{{extinct}}
      }}
      |2={{clade
       |1=[[Gavialoidea]]
       |2={{clade
        |1=''[["Crocodylus" megarhinus]]''{{extinct}}
        |2={{clade
         |1='''Mekosuchinae'''{{extinct}}
         |2=[[Crocodylidae]]
}}}}}}}}}}}}}}}}}}}}
| align="right" width="50%" |
 |}

==Evolutionary history==
===Origins===
[[File:Isisfordia.jpg|thumb|left|Though the origins of Mekosuchinae is unclear, they were unrelated to the Mesozoic crocodylomorphs of Australia like ''Isisfordia''.]]
The shifting phylogenetic position of mekosuchines as well as the poor record of crocodylomorph fossils from Australia have long obscured the origins of the clade. The Mesozoic crocodylomorph record from the continent is solely represented by ''[[Confractosuchus]]'' and ''[[Isisfordia]]'' which, depending on the publication, may either be highly derived non-eusuchian members of [[Neosuchia]] or among the basalmost eusuchians. Regardless, this renders them notably more basal than the later mekosuchines, which are confidently placed among crown crocodilians.<ref name="RM21" /><ref name=LY18/> Following the most common trees in which orientalosuchins are not mekosuchines, the clade at the latest originated during the late [[Danian]], approximately 66 million years ago and around 10 million years before their first confirmed appearance in the fossil record through ''Kambara''. However, if Orientalosuchina is indeed a subclade of mekosuchines, this would push the origins of the clade back into the Cretaceous.<ref name=R23b/>

[[File:Kambara skull.jpg|thumb|The earliest mekosuchines were likely generalists similar to ''Kambara''.]]
The second hypothesis in particular would place the origin of the group in Asia, with the earliest mekosuchines then arriving in Australia before the Eocene. However, Ristevski and colleagues note that the gap between the two continents was substantially greater than it is today, meaning that such a journey would have required the crocodiles to traverse large stretches of ocean, or at the very least do a significant amount of [[island hopping]] (though the presence of islands in this time period is not certain). This manner of travel would in turn profit from at least some form of [[osmoregulation]] being present in early mekosuchines, which is known to be present in gharials and true crocodiles. However, the presence of salt glands as seen in these clades cannot be determined from fossils and with the exception of the insular taxa of the Quaternary all mekosuchines are exclusively known from inland environments. Still, Ristevski and colleagues note that certain extant alligatoroids venture into marine environments, to a lesser extent than true crocodiles, although they lack salt glands. Given that these hypothetical ancestral mekosuchines were likely to have been generalized animals similar to ''Kambara'', it is very possible that they traversed long distances by swimming, possibly with at least some degree of salt tolerance.<ref name=R23b/>

There are still other possibilities for the origin of Mekosuchinae in Australia. For instance, mekosuchines could have hypothetically arrived via land if dispersing from Asia into Europe and then the Americas or directly from Asia into North America. From there, they could have moved to South America, dispersed into Antarctica and entered Australia from the south. However, a key issue with this idea is the complete lack of mekosuchine fossil material from the Americas and Antarctica, rendering dispersal from Asia directly into Australia (or via India) the more likely of the two origins.<ref name=R23b/><ref name=RM21/>

===Diversification and faunal shift===
[[File:Baru wickeni vs "Baru" huberi size.png|thumb|left|By the Oligocene mekosuchines had evolved both dwarf forms and large-prey specialists.]]
While the range and diversity of mekosuchines was still relatively restricted during the Eocene, by the Late Oligocene the group had rapidly diversified into a plethora of different morphotypes ranging from semi-aquatic generalists to large prey specialists, dwarf forms and potentially terrestrial predators.<ref name="W97b" /><ref name=W97/> The origin of this diversification is unclear due to the absence of mekosuchine fossils in the 30 million year gap between the Late Oligocene forms and the earlier ''Kambara.'' However, it is thought that the ancestor of this radiation appeared no later than the middle Eocene. Despite their enormous taxonomic diversity, the range of mekosuchines during this time period was still somewhat limited, with Miocene records primarily stemming from localities in Queensland and the Northern Territory.<ref name=R23b/>

Initially, the transition from the Miocene to the Pliocene was regarded as somewhat of a drop in diversity among mekosuchines as it saw the disappearance of both the large macropredatory ''Baru'' as well as dwarf forms like ''Ultrastenos'', ''Trilophosuchus'' and ''Mekosuchus''.<ref name=Ka17/> The reasons for this wave of extinction may be tied to widespread changes in climate, with both global cooling and the Middle Miocene climate optimum coming to an end. This may have led to an especially harsh but brief period of aridity that saw a retreat of the Australian rainforests and the destruction of the biomes preferred by Miocene mekosuchine groups.<ref name=YRS23/> ''Mekosuchus'' specifically represents somewhat of an outlier, as it only went extinct on the mainland and continued to survive into the Holocene on various Pacific islands. Subsequently, Ristevski and colleagues point out that future finds might show that these animals could have survived for a little longer on the mainland as well.<ref name=R23b/>

While the Miocene-Pliocene transition saw the disappearance of many of the established mekosuchine groups, it did not cause the extinction of the family. ''Quinkana'' survived the initial period of aridification as did other mekosuchines, which in turn gave rise to forms like ''Kalthifrons'' and ''Paludirex''.<ref name=R23b/> Despite the fact that mekosuchines bounced back, they were joined by other groups of crocodilians that made their way to Australia, such as the as of yet unnamed [[Tirari Desert]] species of ''[[Crocodylus]]''. While it was initially hypothesized that the appearance of ''Crocodylus'' in Australia was part of the reason mekosuchines went extinct, there is no actual evidence to suggest a direct link between the two events, with the Tirari Desert taxon likely being entirely unrelated to the crocodiles inhabiting Australia today.<ref name="Ka17" /><ref name=YRS23/>

===Island populations===
{{multiple image
| perrow            = 1/2
| total_width       = 250
| image1            = Royal Davui Island, Fiji - panoramio.jpg
| image2            = New Caledonia - Envisat.jpg
| image3            = Satellite image of Vanuatu in October 1998.jpg
| footer            = By the Pleistocene mekosuchines had colonized various islands in the South Pacific, namely Fiji, New Caledonia and Vanuatu.
| align             = right
}}
Almost as mysterious as the origins of the group is the presence of mekosuchines on distant Pacific islands during the Pleistocene and Holocene. Although multiple examples are known; ''Volia'' from [[Fiji]],<ref name=M02b/> ''Mekosuchus kalpokasi'' from [[Vanuatu]],<ref name=M02/> and ''Mekosuchus inexpectatus'' from [[New Caledonia]];<ref name=BB87/> there is no agreement on how these animals got there from mainland Australia. Just like in discussions about the original colonisation of Australia by the clade, the question of osmoregulation and salt tolerance comes into play when speculating on how these distant islands were colonised. Salisbury and colleagues have previously suggested that ''Mekosuchus'' might have been more salt tolerant due to the lack of permanent freshwater sources on New Caledonia, however, assuming that the genus was more terrestrial as frequently speculated, the absence of fresh water might have been less crucial.

An alternative hypothesis suggests that mekosuchines arrived on Fiji, Vanuatu and New Caledonia through the act of [[oceanic dispersal|rafting]] (being carried there by clinging to drift wood and similar structures) or [[island hopping]]. The latter would have especially profited from lower sea levels during this time period, connecting island chains and providing potential stops along the way. While this dispersal could have happened as early as the Oligocene, it is likely that island mekosuchines were a much more recent development.<ref name="M02" /><ref name="R23b" /><ref name="W97">{{Cite journal|last1=Willis|first1=P. M. A.|year=1997|title=Review of fossil crocodilians from Australasia.|url=https://meridian.allenpress.com/australian-zoologist/article/30/3/287/134518/Review-of-fossil-crocodilians-from-Australasia|journal=Australian Zoologist|volume=30|issue=3|pages=287–298|doi=10.7882/AZ.1997.004|s2cid=84580859 |doi-access=free}}</ref>

===Extinction===
{{multiple image
| perrow            = 1/2
| total_width       = 250
| image1            = Kakadu (AU), Kakadu National Park, Jim Jim Creek -- 2019 -- 4244.jpg
| image2            = Murray River In Drought (4311131550).jpg
| image3            = 2019-20 Australian Bushfires - Kangaroo Island, South Australia (51367525857).jpg
| footer            = Global climate change saw the preferred habitats of mekosuchines destroyed through droughts and fires.
| align             = left
}}
Despite the fact that mekosuchines initially recovered from the aridification that caused the Miocene-Pliocene faunal turnover, the group continued to suffer from the effects of global cooling and Australia's continuous drift north throughout the Pleistocene. This gradual change in climate was felt across most groups of megafauna that inhabited Australia at the time, with the semiaquatic mekosuchines like ''Paludirex'' suffering the most from the disappearance of inland river systems. Hocknull and colleagues write that the [[Lake Eyre Basin]] was among the first systems to rapidly deteriorate some 48.000 years ago, followed shortly by other systems in the next eight thousand years. Rainfall fell to levels far below those of today, deriving the systems of their water supply. This did not change until 30.000 years ago, when it was too late for the systems to recover. While it has been speculated that members of the genus ''Crocodylus'' could have retreated to coastal waters, surviving due to their osmoregulation, while the more freshwater dependant mekosuchines like ''Paludirex'' would have died out as their habitats dried up.<ref name="YRS23" /><ref name=H20/>

This drying may have also affected more terrestrial forms like ''Quinkana''. Despite its inferred lifestyle, members of the genus are still commonly found in close proximity to freshwater and likely inhabited more forested environments. The aridification of Australia led to the collapse of the continents rainforest systems approximately 50.000 years ago and by 44.000 years ago fires had begun to crop up more frequently than before.<ref name=H20>{{Cite journal|last1=Hocknull|first1=Scott A.|last2=Lewis|first2=Richard|last3=Arnold|first3=Lee J.|last4=Pietsch|first4=Tim|last5=Joannes-Boyau|first5=Renaud|last6=Price|first6=Gilbert J.|last7=Moss|first7=Patrick|last8=Wood|first8=Rachel|last9=Dosseto|first9=Anthony|last10=Louys|first10=Julien|last11=Olley|first11=Jon|date=2020-05-18|title=Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration|journal=Nature Communications|volume=11|issue=1|page=2250|doi=10.1038/s41467-020-15785-w|pmid=32418985|pmc=7231803|bibcode=2020NatCo..11.2250H|issn=2041-1723}}</ref> Even before these events, authors note a shift from vine scrubland to more open environments during the Late Pliocene and Early Pleistocene, coinciding with a decrease in known ''Quinkana'' material.<ref name=SPK13/>

In both the instances listed above, human involvement appears to not have been a factor, with Hocknull and colleagues arguing that the two events simply coincided, citing the fact that the megafaunal extinctions on the Australian mainland seemingly ran in the opposite direction of what would be suspected if humans were the driving cause.<ref name=H20/>

[[File:Carte lapita.png|thumb|The Lapita people inhabited large parts of Melanesia and Polynesia, including islands that were home to the last mekosuchines.]]
While mainland mekosuchines died out during the Pleistocene, isolated insular taxa continued to survive, possibly even into the Holocene. The extinction of ''Mekosuchus'' is frequently linked to the arrival of the [[Lapita people]] in the South Pacific, supported by the fact that the range of the genus overlapped with human settlements and by the association of ''M. kalpokasi'' remains with human tools at the [[Arapus archaeological site]] on [[Efate]]. Factors contributing to the disappearance of island mekosuchines range from direct hunting of the crocodiles to habitat destruction and the introduction of invasive species like [[pig]]s and [[rat]]s.<ref name=M02/> However, this idea is not entirely uncontested, as Anderson and colleagues point out that most remains of ''M. inexpectatus'' appear to have been deposited prior to human arrival. They further highlight that no direct evidence for crocodile-human interactions (like butchery marks) exist.<ref name="R23b" /><ref name=A10>{{cite journal |title=Faunal extinction and human habitation in New Caledonia: Initial results and implications of new research at the Pindai Caves |journal=Journal of Pacific Archaeology |year=2010 |last1=Anderson |first1=Atholl |author1-link=Atholl Anderson |last2=Sand |first2=C |last3=Petchey |first3=F |last4=Worthy |first4=T. H |volume=1 |issue=1 |url= https://researchcommons.waikato.ac.nz/handle/10289/5404 |access-date=23 February 2021 }}</ref> The last mekosuchines likely died out approximately 3.000 years ago, with some disputed material suggesting that ''Mekosuchus'' might have even lived until as recently as 1,720 years ago.<ref name="WM97" /><ref name=M02/><ref name="H07" /><ref name=A10/>

==Paleobiology==
===Terrestriality===
Although most mekosuchines exhibit hallmark traits of being semi-aquatic animals, possessing flattened skulls with nares and eyes directed more upward, there are some genera which might suggest that a more land-based lifestyle arose in some branches of the family.

[[File:Americanalligator.jpg|thumb|left|Though still semi-aquatic, ''Kambara'' might have been better adapted at performing the high walk, shown here on an American Alligator.]]
The earliest hints at these derived terrestrial mekosuchines can actually be found in the oldest known member of the family: ''Kambara''. Despite being widely recognized as semi-aquatic with a classically crocodilian head suited for such life, ''Kambara'' also featured certain peculiar adaptations to its limbs that could have facilitated much easier travel across land relative to modern crocodiles. Study of the [[humerus]] has shown that the upper forelimbs could have been swung with much greater force and would have provided greater stability when walking, helping the animal keep its torso off the ground while performing the so-called high walk. At the same time, these adaptations would have positively affected both stride length and walking speed as well. The range of motion of the forelimbs was likewise greater than what is seen in the true crocodiles that inhabit Australia today.<ref name=SSHAG12>{{Cite journal | last1 = Stein | first1 = M. | last2 = Salisbury | first2 = S. W. | last3 = Hand | first3 = S. J. | last4 = Archer | first4 = M. | last5 = Godthelp | first5 = H. | title = Humeral morphology of the early Eocene mekosuchine crocodylian Kambara from the Tingamarra Local Fauna southeastern Queensland, Australia | doi = 10.1080/03115518.2012.671697 | journal = Alcheringa: An Australasian Journal of Palaeontology | pages = 473–486 | year = 2012 | volume = 36 | issue = 4 | bibcode = 2012Alch...36..473S | s2cid = 129195186 }}</ref>

A later study focused on mekosuchines in general; examining material assigned to ''Kambara'', ''Baru'', the "Floraville Taxon" and what might have either been a juvenile ''Baru'' or ''Mekosuchus''; suggests that the group as a whole had collumnar humeri than modern crocodylids with an elliptical rather than rounded cross-section. These factors significantly affect the stress the bones are put under when the animals lift their bodies of the ground, either for a sprawling gait or for the highwalk. The study suggests that the curved humeri of modern crocs serve to provide a more constant core of neutral stress regardless of what gait is assumed by them and provide greater safety when sprawling. Mekosuchines meanwhile appear to have had a lower baseline stress that does not spike as much when switching from one gait to the other, effectively making the highwalk much more viable. The anatomy also seems to support the idea that mekosuchines would have been able to perform the highwalk even after reaching a certain size, while many modern crocodiles cease to move this way after growing too large.<ref name=SHA20>{{Cite journal|last1=Stein |first1=M.D.|last2=Hand|first2=S.J.|last3=Archer|first3=M.|last4=Wroe|first4=S.|last5=Wilson|first5=L.A.B.|year=2020|title=Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb|url=|journal=PeerJ|volume=8 |article-number=e9349 |doi=10.7717/peerj.9349|pmid=32587803 |pmc=7301899 |doi-access=free }}</ref>

All these adaptations, while advantageous for walking on land, do not necessarily show that mekosuchines as a whole were terrestrial,<ref name=SHA20/> rather they show that they were better adapted to walk on land while not negating any of the adaptations for aquatic life. This is somewhat highlighted by the anatomy of the shoulder girdle and hips, which although favouring terrestrial habits in one instance, generally appear very close to those of modern crocodilians.<ref name=SYHA17/> In the case of ''Kambara'' specifically, the hips represent the [[plesiomorphic]] condition and greatly resemble those of gharials and alligators, with later mekosuchines seemingly either diverging into more terrestrial forms or converging with modern crocodiles.<ref name=SYHA17/> Regarding the limbs of ''Kambara'', the same adaptations useful for movement on land also bring advantages for swimming.<ref name=SSHAG12/> Lucas A. Buchanan, who described ''Kambara taraina'', notes in his [[PhD thesis]] that the animal does not show any other notable adaptations for terrestrial life and sticks close to the anatomy of modern salt- and freshwater crocodiles in many aspects. The notion that ''Kambara'' could have possessed a fibular condyle and thus had more hinge-like movement of the knee is entertained, but could not be confirmed due to the preservation of the fossil material.<ref name=B08/> A final clue against overly terrestrial habits in ''Kambara'' is the fact that most individuals are known from a [[Mass mortality event|mass death site]] that preserves the results of a lake drying out, killing the crocodilians that previously inhabited it.<ref name=SW96/><ref name=B08/>

More commonly regarded as terrestrial, albeit not uncontested, are species of the genera ''Trilophosuchus'', ''Mekosuchus'' and ''Quinkana'', each of them supported by multiple lines of reasoning.<ref name=S13/><ref name=W01/><ref name=WPMA93/> One key aspect in favour of terrestrial habits is the skull shape. Unlike most other mekosuchines including ''Kambara'', all three of these taxa had altirostral skulls, meaning the head was comparably boxy and deep rather than flattened.<ref name=M81/><ref name=Br01>{{Cite journal|last1=Brochu|first1=C.A.|year=2001|title=Crocodylian snouts in space and time: phylogenetic approaches toward adaptive radiation|url=https://academic.oup.com/icb/article/41/3/564/2091832|journal=American Zoologist|volume=41|issue=3 |pages=564–585}}</ref>

[[File:Quinkana timara skull.jpg|thumb|Some mekosuchines like ''Quinkana'' might have spent a significant amount of time on land.]]
In Mekosuchus the eyes are large and directed towards the side of the skull while the nostrils open more towards the front, whereas both open more towards the top of the skull in semi-aquatic crocodiles, allowing them to see above the water's surface even if otherwise submerged.<ref name=R23b/> Habitat has also been a factor, with the island of New Caledonia, where ''M. inexpectatus'' lived, lacking in large bodies of freshwater, while Balouet and Buffetaut further point to the well developed muscular insertions.<ref name=BB87/> ''Trilophosuchus'' has a similar skull to ''Mekosuchus'', though the position of the nares is unknown. Study of muscle attachment sites have suggested that ''Trilophosuchus'' held its head much higher than typical for crocodilians, more akin to what is seen in [[agamidae|agamid]] lizards or basking caimans today. Historically, ''Trilophosuchus'' has been compared to both [[Protosuchidae|protosuchids]] and [[notosuchia]]ns, two famously terrestrial groups of Mesozoic crocodylomorphs.<ref name=WPMA93/> Scans of the brain also seem to give clues towards terrestrial life, with brain pneumaticity in particular seemingly correlating with the animals lifestyle. According to Ristevski and colleagues, ''Trilophosuchus'' displays a blend of features of crocodylians and more basal groups. The overall shape of the [[endocast]] resembles ''[[Araripesuchus]]'' and the ratios between the [[inner ear]] elements bears resemblance to [[Baurusuchidae|baurusuchids]] and [[sphenosuchia]]ns. The highly pneumatized skull is compared favorably to notosuchians and, notably, modern [[dwarf caiman]]s and [[dwarf crocodile]]s of the general ''Paleosuchus'' and ''Osteolaemus''.<ref name=R22/> This comparison was not novel and had previously been proposed by Holt in 2007, who suggested that ''Mekosuchus'' may have inhabited small rainforest streams and came out during the night to hunt near the waters edge or on land.<ref name=H07/>

More unconventional is the hypothesis that ''Mekosuchus'' specifically was an arboreal animal,<ref name=W97/> however this idea, first introduced by Willis in 1997, was later argued against by Scanlon<ref name=S14>{{Cite book|last1=Scanlon|first1=J.D.|year=2014|chapter=Giant terrestrial reptilian carnivores of Cenozoic Australia.|url=https://www.researchgate.net/publication/265163781|title=Carnivores of Australia: past, present and future|publisher=CSIRO Publishing|isbn=978-0-643-10317-7}}</ref> and is entirely absent in recent literature including the 2023 work by Jorgo Ristevski (which Willis participated in).<ref name=R23b/>

[[File:Mekosuchine Pelvic Form 4.jpg|thumb|left|Pelvic form four, a fossil that seemingly confirms the presence of terrestrial mekosuchines in the Riversleigh.]]
Much like with ''Mekosuchus'', the idea that ''Quinkana'' was terrestrial is primarily based on the outward appearance of the skull, which is deep and houses rows of ziphodont teeth (meaning they were blade-lake compressed with prominent serrations along the cutting edge). This anatomy drew immediate comparison to [[Sebecidae|sebecids]] and [[Planocraniidae|planocraniids]], two much better understood groups of Cretaceous to Paleogene crocodylomorphs famous for their terrestrial lifestyles.<ref name=M81/> Though the precise use of ziphodont teeth is unclear, several authors have come forward to propose that they may be linked to taking terrestrial prey,<ref name=M81/> chasing prey on land<ref name=SYHA17/> or more broadly that ''Quinkana'' filled a nische similar to modern [[Komodo dragon]]s.<ref name=WM96/><ref name=R23b/> A key issue with the inferred terrestrial habits of ''Quinkana'' is the lack of postcranial material that would be crucial in confirming or debunking these ideas. In the case of planocraniids, the presence of a rounded tail cross-section (rather than laterally flattened) and hoof-like toes both clearly point to terrestrial habits,<ref name=M81/> but no such material is confidently assigned to ''Quinkana''. The closest to ''Quinkana'' postcrania to be found consists of some pelvic remains described as "pelvic form four" by Stein and colleagues in 2017. This pelvis from the Riversleigh WHA is tentatively assigned to ''Quinkana meboldi'' primarily due to its specialized anatomy. Unlike the other pelvic forms discussed by Stein and colleagues (like those of ''Kambara'' and ''Baru''), pelvic form four indicates that the animal it belonged to had a pillar-erect stance and only a limited sprawling gait, similar to what is observed in sebecosuchians. However, while this interpretation would be a dead ringer for the habits inferred for ''Quinkana'' based on its skull, the lack of overlapping material means that the material cannot be confidently assigned to the genus until a skull is actually found in association with postcranial material.<ref name=SYHA17/>

The primary argument against a terrestrial lifestyle for ''Quinkana'' stems from a 2002 publication by Stephen Wroe. In this work, Wroe first argues against a prior argument by Molnar and Willis that reptiles were the top predators of Australia, highlighting the relative rarity of ''Megalania'' and ''Quinkana'' remains to those of marsupials. Wroe further argues that ''Quinkana'' would have been highly dependent on water for protection, mating or thermoregulation and claims that the hoof-like toes of planocraniids were an artifact of preservation.<ref name= W02>{{Cite journal|last=Wroe|first=Stephen|date=2002|title=A review of terrestrial mammalian and reptilian carnivore ecology in Australian fossil faunas, and factors influencing their diversity: the myth of reptilian domination and its broader ramifications|journal=Australian Journal of Zoology|volume=50|issue=1|page=1|doi=10.1071/zo01053|issn=0004-959X}}</ref> While the former point could still be applicable, the latter was eventually combated by [[Christopher Brochu]], who confirmed the authenticity of that morphology.<ref name=B13>{{Cite journal|last1=Brochu|first1=C.A.|year=2013|title=Phylogenetic relationships of Palaeogene ziphodont eusuchians and the status of Pristichampsus Gervais, 1853|url=https://www.researchgate.net/publication/259437003|journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh|volume=103|issue=3–4 |pages=521–550|doi=10.1017/S1755691013000200}}</ref> Naturally, Wroe's arguments do not fully account for Stein's "pelvic form four", described 15 years later.<ref name=SYHA17/>

Overall, current consensus leans towards ''Quinkana'' having had more terrestrial habits, though postcranial material would be needed to fully confirm the hypothesis. Most researchers acknowledge the limited information that can be gathered from skull material alone.<ref name=M81/><ref name=R23b/><ref name=SYHA17/><ref name=WM96/><ref name=M04/>

===Ecology===
Across their existence mekosuchines filled a plethora of different niches in the freshwater ecosystems of Australia, evolving different skull shapes to exploit various food sources and minimize competition. This would have been especially valuable in environments such as the Oligocene and Miocene Riversleigh, where multiple different mekosuchines all inhabited the same areas at the same time.
{{multiple image
| perrow            = 1/2
| total_width       = 250
| image1            = Baru darrowi.png
| image2            = Dromornis stirtoni.jpg
| image3            = Silvabestius-bpk.jpg
| footer            = Fossil evidence shows that ''Baru'' preyed on both flightless birds and large marsupials.
| align             = right
}}

Some mekosuchines, most prominently ''Kambara'' and ''Australosuchus'', possessed platyrostral mesorostrine skulls, meaning their heads were flattened and neither especially elongated nor shortened.<ref name=H05/><ref name=B09/><ref name=WM91/> This morphology, also seen in many modern crocodilians, is generally suited for a more generalist lifestyle, with these animals generally being thought to feed on a wide variety of prey items. ''Kambara'' is among the better studied of the two, with researchers having proposed that the differing types of tooth occlusions seen between species of this genus correlate to slightly altered prey preferences. Lucas A. Buchanan suggests that among the four ''Kambara'' species, those with interlocking teeth (''K. implexidens'' and ''K. taraina'') might be better adapted to grasp and restrain large struggling prey whereas the overbite seen in ''K. murgonensis'' could be employed to cut and slice. Buchanan further notes that among the species with interlocking dentition, ''K. taraina'' had an exceptionally well developed retroarticular process, corresponding to strong pterygoid muscles and thus a stronger bite. Additionally, the musculature used in holding and crushing were also well developed, leading to the hypothesis that ''Kambara taraina'' was especially well suited to tackle larger prey than its relatives.<ref name=B09/> Despite this, little direct evidence of ''Kambara'' feeding habits exists, the one exception being a turtle shell bearing the distinct tooth marks of a crocodile found in the same sediments as the remains of ''Kambara''. The patterns left on the turtle's carapace suggest that ''Kambara'' engaged in behavior known as juggling, the act of repeatedly biting prey in a fashion that would align it with the teeth in the back of the jaw, allowing the animal to break through the robust shell. In the case of this particular fossil, the turtle appears to have survived the initial encounter only to die of an infection later.<ref name=B08>{{cite thesis |last1=Buchanan|first1=L.A.|year=2008|title=The systematics, palaeobiology and palaeoecology of Kambara taraina sp. nov. from the Eocene Rundle Formation, Queensland.|url=https://bridges.monash.edu/articles/thesis/The_systematics_palaeobiology_and_palaeoecology_of_Kambara_taraina_sp_nov_from_the_Eocene_Rundle_Formation_Queensland/4564009|type=PhD thesis|institution=Monash University|location=Melbourne|page=340}}</ref>

This general bauplan is taken a step further by the large ''Paludirex'', which also features a broad and flattened skull, although one that is notably more robust than those of ''Australosuchus'' and ''Kambara''. Given that fact and the shere size of the larger of the two species, ''P. vincenti'', it has been proposed that this genus was specialised in taking larger prey items than its relatives.<ref name=M04/><ref name=R20/><ref name=WM97/>

Another genus of mekosuchine specialised in taking larger prey is ''Baru'', although its anatomy is strikingly different. Unlike the flattened skulls of ''Paludirex'', ''Kambara'' and ''Australosuchus'', the skull of ''Baru'' is described as deep (altirostral) and [[cleaver]]-like with long teeth bearing fine crenulations. These robust jaws, slicing teeth and the pronounced festooning might have aided ''Baru'' in tackling large prey items and dispatching it quickly by inflicting massive amounts of trauma. This hunting method contrasts strongly with the more typical approach of grabbing and drowning, possibly indicating a preference for shallower waters that would render the latter tactic less effective and more risky. Willis and colleagues speculate that ''Baru'' may have been able to tackle prey up to {{convert|300|kg|abbr=on}} in weight and fossil evidence suggests that ''Baru'' fed on marsupials like ''[[Neohelos]]'' and flightless birds like ''[[Emuarius]]'' and ''[[Bullockornis]]''.<ref name=WMM90/><ref name=MVR04/><ref name=Alcoota>{{Cite news|date=2021-05-17|title=Australia crocodile: Skull identified as part of new extinct species|language=en-GB|work=BBC News|url=https://www.bbc.com/news/world-australia-57139281|access-date=2021-05-20}}</ref>

[[File:Komodo Dragon, Komodo, 2016 (08).jpg|thumb|left|''Quinkana'' may have hunted in a manner similar to Komodo dragons.]]
Some of the most specialised anatomy can be seen in ''Quinkana'', suggesting that the genus had a lifestyle drastically different from other mekosuchines. The teeth of ''Quinkana'' are ziphodont, resembling those of terrestrial [[sebecosuchians]], [[Planocraniidae|planocraniids]] and [[monitor lizard]]s, although their precise function is unclear. Molnar has argued that ziphodont dentition indicates an ability to tackle larger prey, terrestrial prey or possibly other crocodilians.<ref name=M81/> Busbey and Willis both draw comparison to modern [[komodo dragon]]s<ref name= WM96/><ref name=R23b/> while Stein and colleagues suggest that ziphodont dentition might be tied to cursorial hunting habits, chasing after prey rather than ambushing it.<ref name=SYHA17>{{Cite journal|last1=Stein|first1=Michael D.|last2=Yates|first2=Adam|last3=Hand|first3=Suzanne J.|last4=Archer|first4=Michael|date=2017|title=Variation in the pelvic and pectoral girdles of Australian Oligo–Miocene mekosuchine crocodiles with implications for locomotion and habitus|journal=PeerJ|volume=5|article-number=e3501|doi=10.7717/peerj.3501|doi-access=free |pmid=28674657|pmc=5494174}}</ref> Murray and Vickers-Rich take a similar approach, but conclude that ''Quinkana'' could have still ambushed prey on land, possibly by lying in wait near [[game trail]]s.<ref name=MVR04>{{Cite book|last1=Murray|first1=P. F.|last2=Vickers-Rich|first2=P. |year=2004|title=Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime|publisher=Indiana University Press|isbn=978-0-253-34282-9}}</ref>

Possibly the most enigmatic mekosuchines in terms of ecology are the dwarf taxa ''Trilophosuchus'' and ''Mekosuchus''. In the case of ''Trilophosuchus'', the study of muscle attachments seems to indicate that rapid sideways movement of the head did play a part in its feeding method, but also showcases that it did not have to face the same resistances as semi-aquatic crocodilians, causing the muscles to be somewhat weaker.<ref name=WPMA93/> Similarly, ''Mekosuchus whitehunterensis''' musculature has been in interpreted as an adaptation to rip flesh from carcasses, either through the same sideways movements as inferred for ''Trilophosuchus'' or by using the traditional crocodilian death roll, although it would have been notably less effective due to the small size of the animal. This would match the fact that shaking seems to be favored by small and juvenile individuals of modern crocodiles. This is further supported by specific adaptations to the muscle attachments in ''M. whitehunterensis'' and the simple fact that the inferred terrestrial habits of the animal would render a death roll much more dangerous if performed on land relative to in the water. Pulling and lifting might have also been a strategy employed by this animal, whether that be to strip the kills of other predators or to dismember its own kills is unclear.<ref name="S13">{{Cite conference|last1=Stein|first1=M. |last2=Yates|first2=A.M.|last3=Scanlon |first3=J.D.| last4=Archer|first4=M. |last5=Willis |first5=P.M.A.|last6=Salisbury|first6=S.|last7=Hand|first7=S.J.|year=2013|title=New materials of Oligo–Miocene Mekosuchus from the Riversleigh World Heritage Area indicate unusual development and palaeoecology.|conference=Proceedings of the 14th Conference on Australasian Vertebrate Evolution, Palaeontology & Systematics|volume=79}}</ref><ref name=SAH15>{{Cite journal|last1=Stein|first1=M.|last2=Archer|first2=M.|last3=Hand|first3=S.J.|year=2016|title=Dwarfism and feeding behaviours in Oligo-Miocene crocodiles from Riversleigh, northwestern Queensland, Australia|url=https://www.app.pan.pl/article/item/app001342014.html|journal=Acta Palaeontologica Polonica|volume=61|issue=1|pages=135–142|doi=10.4202/app.00134.2014|s2cid=55424466 |doi-access=free}}</ref>

{{multiple image
| perrow            = 1/2
| total_width       = 250
| image1            = Mekosuchus holotype.png
| image2            = Christmas Island Red Crab.jpg
| image3            = Placostylus fibratus (MNHN-IM-2000-21343).jpeg
| footer            = The robust jaws and blunt bulbous teeth of ''Mekosuchus inexpectatus'' may have been suited to crush hard-shelled prey like crabs and snails.
| align             = right
}}
There are further important differences between the Neogene mainland species like the aforementioned ''Mekosuchus whitehunterensis'' and the much more recent insular taxa like ''Mekosuchus inexpectatus''. While the former possessed bladed teeth well suited for cutting flesh, the more recent forms appear to have developed more robust cheek teeth that appear more suited for dealing with hard-shelled prey items. This would include various crustaceans, insects and even molluscs<ref name=B91/> like the snail ''[[Placostylus]]'', which is especially common on [[New Caledonia]].<ref name=BB87/> Drawing parallels to dwarf crocodiles and dwarf caimans, Holt and colleagues have suggested that these island forms could have been nocturnal animals, foraging at night near the edge of small streams and on land.<ref name=H07/>

The posterior dentition of ''Volia'' from Fiji might have also been suited to cracking small molluscs and insect cuticles, tho its just as possible that it was a terrestrial hunter, employing its slender, compressed teeth to dispatch of the local giant iguanas and flightless birds.<ref name=B01>{{Cite journal|last1=Burness|first1=G.P.|last2=Diamond|first2=J.|last3=Flannery|first3=T.|year=2001|title=Dinosaurs, dragons, and dwarfs: the evolution of maximal body size.|journal=Proceedings of the National Academy of Sciences|volume=98|issue=25|pages=14518–14523|doi=10.1073/pnas.251548698 |pmid=11724953 |pmc=64714 |bibcode=2001PNAS...9814518B |doi-access=free }}</ref><ref name=M02/>

Despite the broad spectrum of skull forms seen across mekosuchines, not a single taxon has yet been confidently identified as a narrow-snouted fish eater akin to modern gharials or freshwater crocodiles. While this morphology was once applied to ''Ultrastenos'', subsequent fossil finds have shown it to have been a much more generalized animal. ''Harpacochampsa'' meanwhile, historically placed within the family at times, has been more recently interpreted as a type of gharial not dissimilar to the later ''[[Gunggamarandu]]''. There are multiple possible answers to this. On the one hand, it is simply possible that the presence of gharials prevented mekosuchines from trying to compete for this nische, which would not open until the disappearance of gharials during the Pliocene or Pleistocene and be filled by the narrow-snouted freshwater crocodiles. Another possibility is that [[piscivory]] and the associated adaptations would simply not have been a very viable ecology during the time. In the original description of ''Ultrastenos'', it is highlighted how despite the abundance of freshwater biomes, the Riversleigh WHA is poor in fossil fish, with the authors proposing that a narrow rostrum could have been used to catch frogs and other small vertebrates. Notably, the rostra of neither Australian gavialoid are known in full, making the extent of their presumptive longirostry unclear. Finally, a third hypothesis proposes that mekosuchines were simply incapable of developing long and narrow jaws. This may find its reason in the [[ontogeny]] of the animal. A similar situation is seen in alligators, in which certain constraints during development prevent them from evolving this type of head-shape.<ref name="Stein2016"/><ref name=YS24/>

== Paleoenvironment ==
Though the presence of salt glands has been used to explain both the spread of mekosuchines into Australia and their later appearance on islands in the Pacific, genera of this family are generally associated with freshwater environments. This is already apparent in the earliest members, with both ''Kambara murgonensis'' and ''K. implexidens'' having been recovered from the lacustrine [[Tingamarra Local Fauna]]. Given the relatively small size of the local fish, none of which exceed a meter in length, it is thought that the deposits represent a shallow lake, possibly a [[billabong]].<ref name=SSHAG12/> Though it is believed that ''Kambara'' was dependent on freshwater, evidence shows that the environment was subject to dry conditions, in once instance leading to a mass death event.<ref name=SW96/> The younger species ''K. taraina'' and ''K. molnari'', although not [[Sympatry|sympatric]] like their relatives,<ref name=B09/> inhabited the [[Rundle Formation]], interpreted to represent [[lagoon]]al [[mudflats]].<ref name=H05/> Though the similarity has been used as an indicator for the fact that ''Kambara'' was restricted to freshwater, the genus may have nonetheless been more widespread, with Holt and colleagues speculating that the animal might have been common across the inland waterways of Queensland.<ref name=H05/>

=== Riversleigh and Lake Eyre ===
[[File:Gregory River Crossing Riversleigh - panoramio.jpg|thumb|left|Mekosuchines likely inhabited a variety of freshwater environments, from shallow forest pools and oxbow shloughs to meandering rivers.]]
Australian mekosuchines had spread much further inland by the late Oligocene, inhabiting the [[Riversleigh World Heritage Area]] of Queensland and [[Pwerte Marnte Marnte]] in the Northern Territory, as well as various other parts of the [[Lake Eyre Basin]] in southern Australia.<ref name=R23b/> The type of environment present within the Riversleigh has historically been a controversial subject, but seems to represent some type of woodland that appears to have undergone multiple shifts throughout the regions history.<ref name=T09>{{Cite journal|last1=Travouillon|first1=K.J.|last2=Legendre|first2=S.|last3=Archer|first3=M.|last4=Hand|first4=S.J.|year=2009|title=Palaeoecological analyses of Riversleigh's Oligo-Miocene sites: implications for Oligo-Miocene climate change in Australia.|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=276|issue=1–4|pages=24–37|doi=10.1016/j.palaeo.2009.02.025|bibcode=2009PPP...276...24T }}</ref><ref name=Woodhead14/> It has been suggested that Late Oligocene and Early Miocene localities (like Low Lion and Whitehunter, home of taxa like ''Ultrastenos'', ''Mekosuchus whitehunterensis'', ''Baru wickeni'' and ''Quinkana meboldi'') would fall into a dry period, and were thus dominated by open forests and woodlands,<ref name="Stein2016" /><ref name=T09/> possibly also featuring [[sclerophyllous]] vegetation and deciduous vine thickets.<ref name=GH06>{{Cite journal|last1=Guerin|first1=G.R.|last2=Hill|first2=R.S.|year=2006|title=Plant macrofossil evidence for the environment associated with the Riversleigh fauna.|url=https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=2f8e5f3fd5e0b873818b7c02e09aa24057970a68|journal=Australian Journal of Botany|volume=54|issue=8|pages=717–731|doi=10.1071/BT04220|bibcode=2006AuJB...54..717G |url-access=subscription}}</ref> It is thought that the climate grew wetter during Faunal Zones B and C, leading to a more prominent lowland [[rainforest]] environment being present during the deposition of the Ringtail Site (home to ''Trilophosuchus'', ''Baru darrowi'' and ''Mekosuchus sanderi'').<ref name=R23b/> This interpretation of the environment is supported by various factors like the high number of arboreal taxa, overall species richness and the presence of certain rainforest taxa like bubble nesting frogs, [[lyrebirds]] and certain bats. Eventually, the environment appears to have returned to drier open woodlands and forests by the time the Riversleigh transitioned into Faunal Zone D.<ref name=T09/><ref name=Woodhead14/>

The geology of Late Oligocene and Early Miocene sites heavily features lacustrine and fluviate [[calcarenite]]s, which together with the fauna (featuring not only crocodilians but also turtles and lungfish) suggests an important aquatic component,<ref name=Y17/> though other studies have argued for the absence of extensive rivers and wetlands. Still, other bodies of water were clearly present, possibly in the form of forest ponds and lakes.<ref name="Stein2016"/> Similar pools are also known from later sites within the Riversleigh, such as the Ringtail Site, which in addition to crocodilians also preserves the fossils of the extinct [[platypus]] ''Obdurodon dicksoni'', [[lungfish]] and turtles, with the primary terrestrial component of the sites fauna consisting of arboreal [[Phalangeriformes|possum]]s that give the locality its name.<ref name=Woodhead14>{{Cite journal|last1=Woodhead|first1=J.|last2=Hand|first2=S.J.|last3=Archer|first3=M.|last4=Graham|first4=I.|last5=Sniderman |first5=K.| last6=Arena| first6=D.A.|last7=Black|first7=K.H.|last8=Godthelp|first8=H.|last9=Creaser|first9=P.|last10=Price|first10=E.|year=2014|title=Developing a radiometrically-dated chronologic sequence for Neogene biotic change in Australia, from the Riversleigh World Heritage Area of Queensland.|journal=Gondwana Research|volume=29|issue=1|pages=153–167|doi=10.1016/j.gr.2014.10.004|hdl=1959.4/unsworks_36975|hdl-access=free}}</ref>

[[File:Baru Australosuchus distribution.jpg|thumb|The separation of ''Baru wickeni'' and ''Australosuchus clarkae'' may reflect a prominent climate barrier across Oligocene Australia.]]
Other major Late Oligocene localities yielding mekosuchine material include the [[Etadunne Formation|Etadunne]], [[Namba Formation|Namba]] and [[Wipajiri Formation]] of the South Australian Lake Eyre Basin. Like with the Riversleigh, the terrestrial environment has been described as tropical rainforest that was later replaced by dry sclerophyll forest. The aquatic environment was represented by widespread shallow lakes, which were home to a diverse assemblage of [[waterfowl]].<ref name=Worthy09>{{Cite journal|last1=Worthy|first1=T. H.|year=2009|title=Descriptions and phylogenetic relationships of two new genera and four new species of Oligo-Miocene waterfowl (Aves: Anatidae) from Australia|journal=Zoological Journal of the Linnean Society|volume=156|issue=2|pages=411–454|doi=10.1111/j.1096-3642.2008.00483.x}}</ref> However, despite the environmental similarities to the Riversleigh and extensive bodies of freshwater, these southern formations only preserve a single mekosuchine: ''Australosuchus clarkae''.<ref name=WM91/>

The stark contrast between the diverse mekosuchine fauna of the Riversleigh relative to the ''Australosuchus''-dominated southern localities has led to some researchers to speculate on the reason for this divide. Initially, Willis hypothesized that this divide was caused by the localities being situated in different drainage basins, with the crocodilians unable to traverse enough land to spread from one to the other. This hypothesis however would later be debunked by Adam Yates, who described fossil material of ''Baru wickeni'' from the locality of [[Pwerte Marnte Marnte]] within the northern Lake Eyre Basin. Given that this proves the fact that both taxa did at least inhabit the same basin, another hypothesis for the apparent divide was proposed. Yates suggests that rather than being separated by some geographical barrier, the reason why ''Baru'' is restricted to the northern parts of Australia and vice versa lies in the climate of the continent. Yates notes that ''Baru'' is found no further south than 25°S while ''Australosuchus'''s northernmost occurrence lies at 27°S. Furthermore, the southernmost records of ''Australosuchus'' stem from localities at a latitude of 31°S, which accounting for [[continental drift]], would correspond to a latitude of 45° to 50°S during the Oligocene. This is a notably higher latitude than inhabited by any modern crocodilian and may suggest that ''Australosuchus'' was uniquely cold resistant.<ref name=Y17/>

=== Middle Miocene-Pleistocene sites ===
The Middle and Late Miocene record of mekosuchines is primarily known from the localities of Bullock Creek (Camfield Beds) and the Alcoota Fossil site respectively. The former has been interpreted as possible dry vine forest surrounded by scrublands and more open woodlands,<ref name=MVR04/> situated amidst a larger floodplain that featured various freshwater systems such as slow-moving rivers, seasonally shallow lakes, ponds and oxbow [[slough (hydrology)|sloughs]], home to an extensive fauna of small fish and freshwater gastropods.<ref name="Sch16">{{Cite journal |last1=Schwartz |first1=L.R.S. |year=2016 |title=A revised faunal list and geological setting for Bullock Creek, a Camfieldian site from the Northern Territory of Australia. |url=https://search.informit.org/doi/pdf/10.3316/informit.505352092711084 |journal=Memoirs of Museum Victoria |volume=74 |pages=263–290 |doi=10.24199/j.mmv.2016.74.20 |issn=1447-2546|doi-access=free }}</ref> Crocodilians were seemingly separated by habitat preferences, with the gavialoid ''Harpacochampsa'' found in deeper waters like parts of the meandering river and the oxbow sloughs while the mekosuchine ''Baru'' seemingly preferred slow-moving streams in accordance with the hunting style proposed by Willis and colleagues.<ref name=WMM90/><ref name="MMW91">{{Cite journal |last1=Megirian |first1=D. |last2=Murray |first2=P.F. |last3=Willis |first3=P. |year=1991 |title=A new crocodile of the gavial ecomorph morphology from the Miocene of northern Australia |journal=Beagle: Records of the Museums and Art Galleries of the Northern Territory |volume=8 |pages=135–157|doi=10.5962/p.262817 |doi-access=free }}</ref><ref name="MM92">{{Cite journal |last1=Murray |first1=P. |last2=Megirian |first2=D. |year=1992 |title=Continuity and contrast in middle and late Miocene vertebrate communities from the Northern Territory. |url=https://web.archive.org/web/20220302041751id_/https://www.biodiversitylibrary.org/partpdf/263125 |journal=Beagle: Records of the Museums and Art Galleries of the Northern Territory |volume=9 |pages=195–217 |doi=10.5962/p.263125 |issn=0811-3653|doi-access=free }}</ref> Alcoota shares much of its fauna with Bullock Creek, but is notably younger and shows a noticeable drop in freshwater and streambank taxa, which went from making up about half of the Bullock Creek fauna to only about a fourth of Alcoota's, a decline likely tied to the continuous aridification of Australia during this time. Still, the locality is thought to have been lacustrine in nature, featuring permanent bodies of water fed by springs that in times of increased rainfall may have expanded to form an enormous but very shallow lake. The terrestrial biomes of Alcoota may have featured savannah and localized forests according to Murray and Megirian,<ref name=MM92/> while Mao and Retallack propose that the environment was primarily composed of open woodlands and gallery forest, with grasses being fairly rare.<ref name=MR19>{{Cite journal|last1=Mao|first1=X.|last2=Retallack|first2=G.|year=2019 |title= Late Miocene drying of central Australia.|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=514|pages=292–304|doi=10.1016/j.palaeo.2018.10.008|bibcode=2019PPP...514..292M }}</ref>

{{multiple image
| perrow            = 2/2
| total_width       = 350
| image1            = Swamp King (Paludirex gracilis).png
| image2            = Arial view of boat on the wetlands.jpg
| image3            = Forest in Vanuatu.jpg
| image4            = Mekosuchus inexpectans.JPG
| footer            = While continental mekosuchines like ''Paludirex'' (top) largely relied on inland freshwater systems, smaller insular taxa might have found refuge near rainforest streams on islands like Vanuatu (bottom).
| align             = left
}}
One thing showcased by both localities is the impact of the climate change that Australia faced during the Miocene. The presence of certain minerals, namely evaporites and lithoclastic carbonate deposits, seems to suggest that Bullock Creek underwent periods of dry, possibly even semi-arid conditions. The deposits further indicate that these minerals were not formed in a single event, but rather sequentially, possibly due to seasonally changing conditions causing droughts.<ref name="Sch16" /><ref name=MM92/> Similarly, though spring-fed, the freshwater systems of Alcoota were likewise ephemeral and threatened by droughts. The fossil preservation supports this idea, with some remains at Alcoota seemingly deposited during "waterhole tethering", when animals would concentrate and die around slowly shrinking bodies of water, with survivors crushing the remains of the deceased.<ref name=MM92/> It is hypothesized that one especially severe period of aridification was responsible for the extinction of most Oligocene and Miocene mekosuchine groups towards the end of the Miocene.<ref name=YRS23/>

Mekosuchines did however survive this period in less affected areas of Australia and diversified once more during the Pliocene. Taxa of this time period include ''Paludirex'' and ''Kalthifrons'' as well as ''Quinkana'', which survived the Miocene-Pliocene faunal turnover. However, with the exception of the potentially more terrestrial ''Quinkana'', these new forms remained highly dependent on freshwater. Pliocene mekosuchines are known from [[Bluff Downs]] ([[Allingham Formation]]) in Queensland, among other places. Bluff Downs has been interpreted as preserving an environment similar to today's [[Kakadu National Park]], with Thomson and Mackness proposing suggesting the presence of riparian rainforests or vine thickets. Aquatic environments possibly consisted of rivers, creeks and lagoons as indicated by the presence of several species of [[Chelidae|chelid turtles]], [[anhinga]]s and [[pygmy goose|pygmy geese]].<ref name=TM99>{{Cite journal|last1=Thomson|first1=S.A.|last2=Mackness|first2=B.S.|year=1999|title=Fossil Turtles from the Early Pliocene Bluff Downs Local Fauna, with a Description of a New Species of Elseya|url=https://www.academia.edu/75506982|journal=Transactions of the Royal Society of S. Au.|volume=123|issue=3|pages=101–105|via=[[Academia.edu]]}}</ref><ref name=SM01>{{Cite journal | last1 = Scanlon | first1 = J. D. | last2 = MacKness | first2 = B. S. |year = 2001| title = A new giant python from the Pliocene Bluff Downs Local Fauna of northeastern Queensland| journal = Alcheringa: An Australasian Journal of Palaeontology| volume = 25| issue = 4| page = 425|  s2cid = 85185368|doi = 10.1080/03115510108619232| bibcode = 2001Alch...25..425S }}</ref><ref name=BAG08>{{Cite journal|last1=Beck|first1=R.M.D.|last2=Archer|first2=M.|last3=Godthelp|first3=H.|last4= Mackness|first4=B.S.|last5=Hand|first5=S.J.|last6=Muirhead|first6=J.|year=2008|title=A bizarre new family of Marsupialia (incertae sedis) from the early Pliocene of northeastern Australia: implications for the phylogeny of bunodont marsupials.|url=https://www.academia.edu/373085|journal=Journal of Paleontology|volume=82|issue=4|pages=749–762|doi=10.1666/06-124.1 |bibcode=2008JPal...82..749B |via=[[Academia.edu]]}}</ref> Further south, the Lake Eyre Basin also continued to support mekosuchine populations, sharing ''Quinkana'' with Bluff Downs and also preserving the bones of ''Kalthifrons'' as the regions semi-aquatic crocodilian. The [[Tirari Formation]] is noticeably drier than the environment of the underlying Miocene formations inhabited by ''Australosuchus'', but nonetheless much wetter than the region is today. It may have housed fan-deltas, lakes and floodplains,<ref name=NP08>{{Cite journal|last1=Nanson|first1=G.C.|last2=Price|first2=D.M.|last3=Jones|first3=B.G.|last4=Maroulis|first4=J.C.|last5=Coleman|first5=M.| year=2008|title= Alluvial evidence for major climate and flow regime changes during the middle and late Quaternary in eastern central Australia.|url=https://ro.uow.edu.au/cgi/viewcontent.cgi?article=2154&context=scipapers|journal=Geomorphology|volume=101|issue=1 |pages=109–129|doi=10.1016/j.geomorph.2008.05.032 |bibcode=2008Geomo.101..109N |issn=0169-555X}}</ref> and was home to many freshwater taxa beyond the crocodilians, including ducks, flamingos, anhingas, cormorants, egrets and pelicans. Still, the Tirari Formation exemplifies the aridification of Australia, with its freshwater bodies less extensive than the lakes of the Etadunna and Namba Formations that preceded it.<ref name="Wor08">{{Cite journal |last1=Worthy |first1=T.H. |year=2008 |title=Pliocene waterfowl (Aves: Anseriformes) from South Australia and a new genus and species. |url=https://www.researchgate.net/publication/230558777 |journal=Emu - Austral Ornithology |volume=108 |issue=2 |pages=153–165|doi=10.1071/MU07063 |bibcode=2008EmuAO.108..153W }}</ref> The Tirari Formation and ''Kalthifrons'' are furthermore key examples for the threat that aridification continued to pose to mekosuchines, with the type locality of ''Kalthifrons'' representing a watering hole that dried up in a drought, killing the aquatic taxa that lived in it.<ref name=Ka17/>

During the Pleistocene, aridification caused another extinction event among mekosuchines. Given the groups preference for the inland freshwater systems of Australia, the collapse of said systems and associated change to more open environments wiped out both semi-aquatic taxa like ''Paludirex'' as well as the more terrestrial ''Quinkana''. Though rainfall eventually increased again, settling on the levels of precipitation seen today, this was too late to save ''Australia'''s inland freshwater systems.<ref name=R20/><ref name="SPK13" /><ref name=H20/>

Animals like ''Mekosuchus inexpectatus'' were the last mekosuchines, and inhabited the tropical islands of the South Pacific like Vanuatu, Fiji and New Caledonia. They may have lived in the rainforests of these islands, spending their life in or close to small rainforest streams.<ref name=H07/>

==References==
{{reflist}}

{{Extinct Crocodilia|B.}}
{{Taxonbar|from=Q137778}}

[[Category:Mekosuchinae| ]]
[[Category:Enigmatic crocodilian taxa]]
[[Category:Ypresian first appearances]]
[[Category:Paleogene crocodylomorphs]]
[[Category:Neogene crocodylomorphs]]
[[Category:Holocene extinctions]]