Falcatus Falcatus 01

''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

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. Falcatus was a chondricthian known as a " cladodont-toothed stethacanthid holocephalan". 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 condrichthyan 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.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.

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. This means that this fish was more closely related to Chimaeras than to true sharks.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 Other members of its family include '' Ozarcus'' from the Carboniferous of Arkansas, and '' Cretacladoides'' from the Cretaceous of Austria.

Paleoecology

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. 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. Another theory is that the bottom of the bay created mudslides because of heavy rainfall, which rapidly buried the creatures. However, because many of the fish fossils were found with distended gills, this would suggest death by asphyxiation. Falcatus lived alongside many strange creatures like the chondrichthyans '' Agassizodus,'' '' Listracanthus'' and ''Delphyodontos.'' It also lived alongside many ray-finned fish like '' Discoserra'' and ''Paratarrasius''.' Other fish included the rhabdodermatid ''Cardiosuctor'','''' the rhizodont ''Strepsodus,'' and ''Hardistiella'', one of the oldest known lamprey. The invertebrates of bear gulch were very diverse creatures, like the hoplocarids, which include modern day mantis shrimp, ''Anderella'', which is the youngest known synziphosurine'''' and more enigmatic creatures like ''Typhloesus,'' and the ¨Square objects¨ which might be sea slaps or cnidarians. Other inverts include, mollusks like the nautiloid ''Tylonautilus,'' pterioid bivalves which have been found encrusting '' sargassum'' like brown algae'''' as well as productid brachiopods, ''Paleolimulus'','''' phyllocarids and echinoderms like Crinoids, echinoids, sea stars, brittle stars and a many armed starfish called ''Lepidasterella montanensis.''

File:†Aenigmacaris_cornigerum_SCHRAM_&_HORNER_1979.jpg, '' Aenigmacaris cornigerum'' from Bear Gulch

References

* David Norman. (2001): The Big Book Of Dinosaurs. Pg.84 and Pg.286, Walcome books.

External links

* http://www.elasmo-research.org/education/evolution/golden_age.htm
* https://web.archive.org/web/20070927011823/http://comenius.susqu.edu/biol/202/Animals/DEUTEROSTOMES/CRANIATA/CHONDRICHTHYES.htm

{{Taxonbar, from=Q144625

Symmoriiformes
Carboniferous fish of North America
Fossil taxa described in 1985