Falcatus

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Falcatus is an extinct genus of falcatid chondrichthyan which lived during the early Carboniferous Period in Bear Gulch bay in what is now Montana.

Description

Illustration - Falcatus falcatus
Life restoration of female (top) and male (bottom)
File:Falcatus falcatus 01.JPG
Falcatus falcatus male. Lower Carboniferous, Montana, USA

This fish was quite small, only getting to around 25–30 cm or 10-12 inches long. This is about as big as some of the smallest sharks around today, like the pygmy laternshark.[1] Falcatus was a chondrichthyan known as a "cladodont-toothed stethacanthid holocephalan".[2] The first material known from the genus were the prominent fin spines that curve anteriorly over the head of the animal. When first described in 1883 from the St. Louis Limestone, these remains were given the name Physonemus falcatus. However, in 1985, fossils of a new type of chondrichthyan from Montana were described that displayed a high degree of sexual dimorphism. The same spines that were previously named P. falcatus were found on one of the morphs, identified as the male due to the presence of valvae.[3]

Classification

Despite often being called a shark, Falcatus and its relatives were part of the order Symmoriiformes, which itself was part of the subclass Holocephali.[3] This means that this fish was more closely related to Chimaeras than to true sharks.[4] Other members of its family include Ozarcus from the Carboniferous of Arkansas,[5] and potentially Cretacladoides from the Cretaceous of Austria.[6]

File:StethacanthusesDB 2.jpg
Two Stethacanthus species, S. altonensis and S. productus, lived alongside Falcatus

Paleoecology

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The bear gulch limestone is a fossil deposit from the Big Snowy Mountains of Montana. It is a smaller part of the larger St. louis limestone, which dates to the middle carboniferous. During the time, the area was a series of mudflats and lagoons with brackish and freshwater.[7] Many theories have been put forth for the preservation. One is that the creatures sank to the bottom and died of asphyxiation in the oxygen poor waters, being preserved without scavenging took place.[8] Another theory is that the bottom of the bay created mudslides because of heavy rainfall, which rapidly buried the creatures.[9] However, because many of the fish fossils were found with distended gills, this would suggest death by asphyxiation.[10] Falcatus lived alongside many strange creatures like the chondrichthyans Agassizodus, Listracanthus[11] and Delphyodontos.[12] It also lived alongside many ray-finned fish like Discoserra[13] and Paratarrasius.[14] Other fish included the rhabdodermatid Cardiosuctor,[15] the rhizodont Strepsodus,[16] and Hardistiella, one of the oldest known lamprey.[17] The invertebrates of bear gulch were very diverse creatures, like the hoplocarids (relatives of the mantis shrimp),[18] Anderella, which is the youngest known synziphosurine[19] and more enigmatic creatures like the potential gastropod relative Typhloesus,[20] and the "Square objects" which might be sea salps or cnidarians.[21] Other inverts include, mollusks like the nautiloid Tylonautilus,[22] pterioid bivalves which have been found encrusting sargassum like brown algae[23] as well as productid brachiopods,[24] Paleolimulus,[25] phyllocarids[26] and echinoderms like Crinoids, echinoids, sea stars, brittle stars and a many armed starfish called Lepidasterella montanensis.[27]

References

  • David Norman. (2001): The Big Book Of Dinosaurs. Pg.84 and Pg.286, Walcome books.
  1. ↑ Script error: No such module "citation/CS1".
  2. ↑ Script error: No such module "citation/CS1". Fossil Fish of Bear Gulch 2005 by Richard Lund and Eileen Grogan Accessed 2009-01-14
  3. ↑ a b The morphology of Falcatus falcatus (St. John and Worthen), a Mississippian stethacanthid chondrichthyan from the Bear Gulch Limestone of Montana. Journal of Vertebrate Paleontology 5(1):1-19.
  4. ↑ Coates, M., Gess, R., Finarelli, J., Criswell, K., Tietjen, K. 2016. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature. doi: 10.1038/nature20806
  5. ↑ Script error: No such module "Citation/CS1".
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  7. ↑ Script error: No such module "citation/CS1".
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  9. ↑ Script error: No such module "Citation/CS1".
  10. ↑ Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "Citation/CS1".
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  14. ↑ Script error: No such module "Citation/CS1".
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  16. ↑ Script error: No such module "Citation/CS1".
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  18. ↑ Script error: No such module "Citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".
  20. ↑ Script error: No such module "Citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "Citation/CS1".
  23. ↑ Script error: No such module "Citation/CS1".
  24. ↑ Script error: No such module "Citation/CS1".
  25. ↑ Script error: No such module "Citation/CS1".
  26. ↑ Script error: No such module "Citation/CS1".
  27. ↑ Script error: No such module "Citation/CS1".

External links

Script error: No such module "Portal". Template:Chondrichthyan genera Template:Taxonbar

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