View source for Craniate

{{Short description|Proposed clade of chordates, member of the Craniata}}
{{Redirect|Craniata|a [[Class (biology)|class]] of [[Brachiopoda|Brachiopod]]|Craniforma}}{{For|an explanation of its other name|Vertebrate}}{{Automatic taxobox
| fossil_range = <br>[[Cambrian Stage 3]]&ndash;[[Holocene|Present]],<br>{{fossil range|518|0|earliest= 525|ref=<ref name="Yang2018">{{Cite journal|last1=Yang|first1=Chuan|last2=Li|first2=Xian-Hua|last3=Zhu|first3=Maoyan|last4=Condon|first4=Daniel J.|last5=Chen|first5=Junyuan|date=2018|title=Geochronological constraint on the Cambrian Chengjiang biota, South China|journal=Journal of the Geological Society|language=en|volume=175|issue=4|pages=659–666|doi=10.1144/jgs2017-103|bibcode=2018JGSoc.175..659Y|s2cid=135091168|issn=0016-7649|url=http://nora.nerc.ac.uk/id/eprint/521412/1/2018-JGS-Chuan%20Yang%20et%20al.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://nora.nerc.ac.uk/id/eprint/521412/1/2018-JGS-Chuan%20Yang%20et%20al.pdf |archive-date=2022-10-09 |url-status=live}}</ref>}}
| name = Craniates
| image = Pacific hagfish Myxine.jpg
| image_caption = A [[Pacific hagfish]], an example of (what was thought to be) a "non-vertebrate craniate"
| taxon = Craniata
| authority = Lankester, 1877<ref name="Nielsen2012">{{Cite journal
   | title = The authorship of higher chordate taxa
   | author = Nielsen, C.
   | journal = Zoologica Scripta
   | volume = 41 | issue = 4 | pages = 435–436
   | date = July 2012
   | doi = 10.1111/j.1463-6409.2012.00536.x
 | s2cid = 83266247
 }}</ref>
| subdivision_ranks = Included groups
| subdivision = *[[Agnatha]]
** [[Hyperoartia]] ([[lamprey]]s) {{small|(disputed vertebrates)}}
** [[Myxini]] (hagfishes)
** [[Cephalaspidomorphi]] {{small|(possible vertebrates)}}
*** [[Gnathostomata]] {{small|(emerged from within Cephalaspidomorphi)}}<ref>{{Cite journal|last=Miyashita|first=Tetsuto|date=2019|title=Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=116|issue=6|pages=2146–2151|doi=10.1073/pnas.1814794116|pmid=30670644|pmc=6369785|bibcode=2019PNAS..116.2146M|doi-access=free}}</ref>
| synonyms = *   Craniota {{small|Haeckel, 1866}}
*   Pachycardia {{small|Haeckel, 1866}}
*   [[Vertebrata]] {{small|J-B. Lamarck, 1801}}
}}

A '''craniate''' is a member of the '''Craniata''' (sometimes called the '''Craniota'''), a proposed [[clade]] of [[chordate]] [[animal]]s with a [[skull]] of hard [[bone]] or [[cartilage]]. Living representatives are the [[Myxini]] (hagfishes), [[Hyperoartia]] (including [[lamprey]]s), and the much more numerous [[Gnathostomata]] (jawed vertebrates).<ref name="Campbell & Reece 2005 p. 676">Campbell & Reece 2005 p. 676</ref><ref>Cracraft & Donoghue 2004 p. 390</ref> Formerly distinct from [[vertebrate]]s, which excluded [[hagfish]], however molecular and anatomical research in the 21st century has led to the reinclusion of hagfish as vertebrates, making living craniates synonymous with living vertebrates.

The clade was conceived largely on the basis of the Hyperoartia (lampreys and kin) being more closely related to the Gnathostomata (jawed vertebrates) than the Myxini (hagfishes). This, combined with an apparent lack of vertebral elements within the Myxini, suggested that the Myxini were descended from a more ancient lineage than the vertebrates, and that the skull developed before the [[vertebral column]]. The clade was thus composed of the Myxini and the [[vertebrate]]s, and any extinct chordates with skulls.

However recent studies using [[molecular phylogenetics]] have contradicted this view, with evidence that the [[Cyclostomata]] ([[Hyperoartia]] and Myxini) is [[Monophyly|monophyletic]]; this result suggests that the Myxini are degenerate vertebrates, and therefore that vertebrates and craniates are cladistically equivalent, at least for the living representatives. The placement of the Myxini within the vertebrates has been further strengthened by recent anatomical analysis, with vestiges of a vertebral column being discovered in the Myxini.<ref name="Janvier2011">{{cite journal|last1=Janvier|first1=Philippe|title=Comparative Anatomy: All Vertebrates Do Have Vertebrae|journal=Current Biology|volume=21|issue=17|year=2011|pages=R661–R663|issn=0960-9822|doi=10.1016/j.cub.2011.07.014|pmid=21920298|s2cid=17652802|doi-access=free|bibcode=2011CBio...21.R661J }}</ref>

==Characteristics==
In the simplest sense, craniates are chordates with well-defined heads, thus excluding members of the chordate subphyla [[Tunicata]] (tunicates) and [[Cephalochordata]] (lancelets), but including [[Myxini]], which have cartilaginous crania and tooth-like structures composed of [[keratin]]. Craniata also includes all [[Cephalaspidomorphi|lampreys and armoured jawless fishes]], [[Placodermi|armoured jawed fish]], [[Chondrichthyes|sharks, skates, and rays]], and [[Teleostomi|teleostomians:]] [[Acanthodii|spiny sharks]], [[Osteichthyes|bony fish]], [[lissamphibia]]ns, [[Temnospondyli|temnospondyls]] and [[Parareptiles|protoreptiles]], [[sauropsids]] and [[mammal]]s. The craniate head consists of a three-part [[brain]], [[neural crest]] which gives rise to many cell lineages, and a cranium.<ref>Campbell & Reece 2005 pp. 675–7</ref><ref>Parker & Haswell 1921</ref>

In addition to distinct crania (sing. ''[[cranium]]''), craniates possess many derived characteristics, which have allowed for more complexity to follow. [[Molecular biology|Molecular-genetic]] analysis of craniates reveals that, compared to less complex animals, they developed duplicate sets of many [[gene]] families that are involved in [[cell signaling]], [[Transcription (genetics)|transcription]], and [[morphogenesis]] (see [[homeobox]]).<ref name="Campbell & Reece 2005 p. 676" />

In general, craniates are much more active than tunicates and lancelets and, as a result, have greater metabolic demands, as well as several anatomical adaptations. Aquatic craniates have gill slits, which are connected to muscles to pump water through the slits, engaging in both feeding and gas exchange (as opposed to lancelets, whose [[pharyngeal slit]]s are used only for suspension feeding, chiefly by cilia-mucus rather than muscles). Muscles line the alimentary canal, [[Peristalsis|moving]] food through the canal, allowing higher craniates such as mammals to develop more complex digestive systems for optimal food processing. Craniates have cardiovascular systems that include a heart with at least two chambers, [[red blood cells]], oxygen transporting [[hemoglobin]] as well as [[myoglobin]], [[liver]]s and [[kidney]]s.<ref name="Campbell & Reece 2005 p. 676" />

==Systematics and taxonomy==
[[File:Figure 29 01 05.jpg|thumb|300px| Craniata, including this [[Placodermi|placoderm]] fish (''[[Dunkleosteus]]'' sp.), are characterized by the presence of a cranium, mandible, and other facial bones.<ref>[https://cnx.org/contents/VB2yhrAh@8/Chordates Chordates] ''OpenStax'', 9 May 2019.</ref> ]]

[[Carl Linnaeus|Linnaeus]] (1758) classified hagfishes as [[Vermes]], a [[Class (biology)|class]] for non-arthropod invertebrates (in modern nomenclature).<ref>{{Cite book |last=Linnaeus |first=Carolus |title=Systema Naturae |year=1758 |edition=10 |language=la}}</ref>

[[André Marie Constant Duméril|Dumeril]] (1806)<ref name="Janvier">{{Cite web |last=Janvier |first=Philippe |title=Craniata - Animals with skulls |url=http://tolweb.org/Craniata |website=Tree of Life Web Project (ToL) |publisher=Tree of Life Web Project}}</ref> grouped hagfishes and lampreys in the taxon Cyclostomi, characterized by horny teeth borne on a tongue-like apparatus, a large notochord as adults, and pouch-shaped gills (Marspibranchii). [[Cyclostomata|Cyclostome]]s were regarded as either degenerate cartilaginous fishes or primitive vertebrates. [[Edward Drinker Cope|Cope]] (1889)<ref name="Janvier"/> coined the name [[Agnatha]] ("jawless") for a group that included the cyclostomes and a number of fossil groups in which jaws could not be observed. Vertebrates were subsequently divided into two major sister-groups: the Agnatha and the Gnathostomata (jawed vertebrates). [[Erik Stensiö|Stensiö]] (1927)<ref name="Janvier"/> suggested that the two groups of living agnathans (i.e. the cyclostomes) arose independently from different groups of fossil agnathans.

[[Søren Løvtrup|Løvtrup]] (1977)<ref name="Janvier"/> argued that lampreys are more closely related to gnathostomes based on a number of uniquely derived characters, including:

*Arcualia (serially arranged paired cartilages above the notochord)
*Extrinsic eyeball muscles
*Radial muscles in the fins
*A closely set atrium and ventricle of the [[heart]]
*Nervous regulation of the heart by the [[vagus nerve]]
*A [[typhlosole]] (a spirally coiled valve of the intestinal wall)
*True [[lymphocyte]]s
*A differentiated anterior lobe of the pituitary gland ([[adenohypophysis]])
*Three inner ear maculae (patches of acceleration sensitive 'hair cells' used in balance) organized into two or three vertical [[semicircular canals]] 
*[[Neuromast]] organs (composed of vibration sensitive hair cells) in the laterosensory canals
*An electroreceptive [[lateral line]] (with voltage sensitive hair cells)
*Electrosensory lateral line nerves
*A [[cerebellum]], i.e. the multi-layered roof of the hindbrain with unique structure (characteristic neural architecture including direct inputs from the lateral line and large output Purkinje cells) and function (integrating sensory perception and coordinating motor control)

In other words, the cyclostome characteristics (e.g. horny teeth on a "tongue", gill pouches) are either instances of convergent evolution for feeding and gill ventilation in animals with an eel-like body shape, or represent primitive craniate characteristics subsequently lost or modified in gnathostomes. On this basis [[Philippe Janvier|Janvier]] (1978){{Citation needed|date=August 2024}} proposed to use the names ''Vertebrata'' and ''Craniata'' as two distinct and nested taxa.

==Validity==
The validity of the taxon "Craniata" was recently examined by Delarbre et al. (2002) using [[mtDNA]] [[DNA sequence|sequence]] data, concluding that Myxini is more closely related to [[Hyperoartia]] than to Gnathostomata - i.e., that modern jawless fishes form a clade called [[Cyclostomata]]. The argument is that, if Cyclostomata is indeed monophyletic, Vertebrata would return to its old content ([[Gnathostomata]] + [[Cyclostomata]]) and the name Craniata, being superfluous, would become a junior synonym.

The new evidence removes support for the hypothesis for the evolutionary sequence by which (from among [[tunicate]]-like chordates) first the hard cranium arose as it is exhibited by the hagfishes, then the backbone as exhibited by the lampreys, and then finally the hinged jaw that is now ubiquitous. In 2010, [[Philippe Janvier]] stated:
{{quote|Although I was among the early supporters of vertebrate paraphyly, I am impressed by the evidence provided by Heimberg et al. and prepared to admit that cyclostomes are, in fact, monophyletic. The consequence is that they may tell us little, if anything, about the dawn of vertebrate evolution, except that the intuitions of 19th century zoologists were correct in assuming that these odd vertebrates (notably, hagfishes) are strongly degenerate and have lost many characters over time.<ref>"MicroRNAs revive old views about jawless vertebrate divergence and evolution." Proceedings of the National Academy of Sciences (USA) 107:19137-19138. [http://www.pnas.org/content/107/45/19137.full.pdf+html]</ref>}}

==Classification==
Below is a [[phylogenetic tree]] of the phylum [[Chordata]]. Lines show probable evolutionary relationships, including extinct taxa, which are denoted with a [[Dagger (typography)|dagger]], †. Some groups in this tree ([[lancelets]] and [[tunicates]]) are invertebrates. The positions (relationships) of the lancelet, tunicate, and craniate clades are as reported.<ref>{{Cite journal | title=The amphioxus genome and the evolution of the chordate karyotype
 | author=Putnam, N. H. | author2=Butts, T. | author3=Ferrier, D. E. K. | author4=Furlong, R. F. | author5=Hellsten, U. | author6=Kawashima, T. | author7=Robinson-Rechavi, M. | author8=Shoguchi, E. | author9=Terry, A. | author10=Yu, J. K. | author11=Benito-Gutiérrez, E. L. | author12=Dubchak, I. | author13=Garcia-Fernàndez, J. | author14=Gibson-Brown, J. J. | author15=Grigoriev, I. V. | author16=Horton, A. C. | author17=De Jong, P. J. | author18=Jurka, J. | author19=Kapitonov, V. V. | author20=Kohara, Y. | author21=Kuroki, Y. | author22=Lindquist, E. | author23=Lucas, S. | author24=Osoegawa, K. | author25=Pennacchio, L. A. | author26=Salamov, A. A. | author27=Satou, Y. | author28=Sauka-Spengler, T. | author29=Schmutz, J. | author30=Shin-i, T. | journal=Nature | volume=453 | issue=7198 | pages=1064–1071 | date=19 June 2008
 | bibcode=2008Natur.453.1064P | doi=10.1038/nature06967 | pmid=18563158| doi-access=free }}</ref><ref>{{Cite journal | title=Cyclostome embryology and early evolutionary history of vertebrates | author=Ota, K. G. | author2=Kuratani, S. | journal=Integrative and Comparative Biology | volume=47 | issue=3 | pages=329–337 | date=September 2007 | doi=10.1093/icb/icm022 | pmid=21672842| doi-access=free }}</ref><ref>{{cite journal|vauthors=Delsuc F, Philippe H, Tsagkogeorga G, Simion P, Tilak MK, Turon X, López-Legentil S, Piette J, Lemaire P, Douzery EJ|date=April 2018|title=A phylogenomic framework and timescale for comparative studies of tunicates|journal=BMC Biology|volume=16|issue=1|page=39|doi=10.1186/s12915-018-0499-2|pmc=5899321|pmid=29653534 |doi-access=free }}</ref> Note that [[Placodermi]] is now thought to be [[paraphyletic]].<ref>{{cite journal |last1=Li |first1=Qiang |last2=Zhu |first2=You-an |last3=Lu |first3=Jing |last4=Chen |first4=Yang |last5=Wang |first5=Jianhua |last6=Peng |first6=Lijian |last7=Wei |first7=Guangbiao |last8=Zhu |first8=Min |title=A new Silurian fish close to the common ancestor of modern gnathostomes |journal=Current Biology |date=August 2021 |volume=31 |issue=16 |pages=3613–3620.e2 |doi=10.1016/j.cub.2021.05.053 |pmid=34146483 |s2cid=235477130 |doi-access=free |bibcode=2021CBio...31E3613L }}</ref><ref name="Giles et al 2015">{{closed access}} {{cite journal |last1=Giles |first1=Sam |last2=Friedman |first2=Matt |last3=Brazeau |first3=Martin D. |title=Osteichthyan-like cranial conditions in an Early Devonian stem gnathostome |journal=[[Nature (journal)|Nature]] |volume=520 |issue=7545 |pages=82–85 |date=2015-01-12 |issn=1476-4687  |doi=10.1038/nature14065 |pmid=25581798 |pmc=5536226 |bibcode=2015Natur.520...82G }}</ref>

{{clade| style=font-size:85%;line-height:85%
|1={{clade
   |1=[[Cephalochordate|Cephalochordata]] ([[lancelets]]) [[File:Branchiostoma cultellus.jpg|80 px]]
 |label2=[[Olfactores]]
   |2={{clade
|1=[[Tunicata]] (tunicates: [[sea squirts]], [[Thaliacea|thaliaceans]], [[larvaceans]]) [[File:Salpa scheme.png|60 px]]  
|label2=[[Vertebrate|Vertebrata]]/
   |sublabel2='''Craniata'''
|2={{clade
   |label1=[[Agnatha]]/
   |sublabel1=[[Cyclostomes]]
   |1={{clade
| 1=[[Hagfish|Myxini]] ([[hagfishes]])  <span style="{{MirrorH}}">[[File:Cuvier-120-Myxine116.jpg|90 px]]</span>
     | 5=[[Hyperoartia]]/Petromyzontida ([[lampreys]]) <span style="{{MirrorH}}">[[File:Petromyzon marinus.jpg|80 px]]</span>
}}
   | 2={{clade
     | 1=†[[Osteostraci]] [[File:Tremataspis NT small.jpg|70 px]]
     | label2=[[Gnathostomata]]
     | 2={{clade
       | state1=double
       | 1=†[[Placodermi]] [[File:Dunkleosteus terrelli 2023 reconstruction.png|70 px]]
       | 2={{clade
           |1=[[Chondrichthyes]] (cartilaginous fishes) <span style="{{MirrorH}}">[[File:White shark (Duane Raver).png|70 px]]</span>
           |label2=[[Osteichthyes]]/
           |sublabel2=[[Euteleostomi]]
           |2={{clade
              |1=[[Actinopterygii]] (ray-finned fishes) [[File:Atlantic sturgeon flipped.jpg|70 px]]
              |2=[[Sarcopterygii]] (lobe-finned fishes and [[tetrapods]]) <span style="{{MirrorH}}">[[File:Coelacanth.png|55 px]]</span> <span style="{{MirrorH}}">[[File:Deinosuchus riograndensis.png|90px]]</span>
              }}
           }}
        }}
     }}
  }}
}}
}}
|label1=[[Chordata]]}}

==See also==
*''[[Haikouella]]'', extinct genus
*''[[Haikouichthys]]'', extinct genus

== Notes ==
{{Reflist|30em}}

== References ==
{{Wikispecies|Chordata Craniata}}
*{{Cite book| title = Biology| edition = Seventh
 | last1 = Campbell | first1 = Neil A.
 | last2 = Reece | first2 = Jane B.
 | author1-link = Neil Campbell (scientist)
 | author2-link = Jane Reece
 | year = 2005
 | publisher = [[Pearson Education|Benjamin Cummings]] | location = San Francisco CA
 }}
*{{Cite book| title = Animal Diversity| edition = Fourth
 |author=Cleveland, P. |author2=Hickman, J. |author3=Roberts, L. S. |author4=Keen, S. L. |author5=Larson, A. |author6=Eisenhour, D. J.
 | year = 2007
 | publisher = [[McGraw Hill]] | location = New York
 }}
*{{Cite book| title = Assembling the Tree of Life
 | author1 = Cracraft, Joel
 | author2 = Donoghue, Michael J.
 | year = 2004
 | publisher = Oxford University Press US | location = New York
 | url = https://books.google.com/books?id=_jLl8zIRzucC&q=hagfish%2Bcraniata&pg=PA390
 | isbn = 978-0-19-517234-8
 }}
*{{Cite journal| title = Complete Mitochondrial DNA of the Hagfish, Eptatretus burgeri: The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly
 | last1 = Delarbre | first1 = Christiane
 | last2 = Gallut | first2 = C
 | last3 = Barriel | first3 = V
 | last4 = Janvier | first4 = P
 | last5 = Gachelin | first5 = G
 | display-authors = etal
 | journal = Molecular Phylogenetics and Evolution
 | year = 2002 | volume = 22 | issue = 2 | pages = 184–192
 | doi = 10.1006/mpev.2001.1045 | pmid = 11820840
 | bibcode = 2002MolPE..22..184D }}
*{{Cite book| title = A Text-book of Zoology
 | last1 = Parker | first1 = T. J.
 | last2 = Haswell | first2 = W. A.
 | author2-link = William Aitcheson Haswell
 | year = 1921
 | publisher = Macmillan & Co.
 }}

{{Animalia}}
{{Chordata}}

{{Taxonbar|from=Q84149}}

[[Category:Chordates]]
[[Category:Extant Cambrian first appearances]]