''Falcatus'' is an extinct genus of falcatid chondrichthyan which lived during the early

Carboniferous Period The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonif ...

in Bear Gulch bay in what is now

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

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 This is a typical Cladodont tooth, of a shark called ''Glikmanius''">Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius'' Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a com ...

-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 The St. Louis Limestone is a large geologic formation covering a wide area of the midwest of the United States. It is named after an exposure at St. Louis, Missouri. It consists of sedimentary limestone with scattered chert beds, including t ...

, these remains were given the name ''Physonemus falcatus''. However, in 1985, fossils of a new type of condrichthyan from

were described that displayed a high degree of

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

. 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 Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. A ...

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 ''Ozarcus'' is an extinct genus of symmoriiform from the Carboniferous period of Arkansas. The type species, ''Ozarcus mapesae'', was named in 2014 based on cartilaginous skulls from the Serpukhovian-age Fayetteville Formation. The genus is na ...

'' from the Carboniferous of

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the O ...

, and ''

Cretacladoides ''Cretacladoides'' ("cladodont likeness from the Cretaceous") is a genus of chondrichthyan, possibly a falcatid, found in France and Austria. Known solely from teeth, mainly found in the Klausrieglerbach locality of Austria, it consists of two ...

'' from the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

of Austria. StethacanthusesDB_2

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 Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can ...

in the

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

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 ''Agassizodus'' is an extinct genus of eugeneodont holocephalan from the Carboniferous. It belongs to the family Helicoprionidae, which is sometimes called Agassizodontidae. Like other members of its family, it possessed a symphyseal tooth whorl ...

,'' ''

Listracanthus ''Listracanthus'' is a genus of extinct chondrichthyan with uncertain affinities. Species of ''Listracanthus'' are known primarily from their tremendous, feather-like denticles, which range up to four inches in length. The denticles had a larg ...

'' and '' Delphyodontos.'' It also lived alongside many

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...

like '' Discoserra'' and ''Paratarrasius''.' Other fish included the rhabdodermatid ''Cardiosuctor'','''' the rhizodont '' Strepsodus,'' and '' Hardistiella'', one of the oldest known

lamprey Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...

. The

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

of bear gulch were very diverse creatures, like the hoplocarids, which include modern day

mantis shrimp Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 340 million years ago. Mantis shrimp typically grow to around in length, ...

, ''

Anderella ''Anderella'' is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. ''Anderella'' was regarded as part of the clade Prosomapoda. Fossils of the single and type species, ''A. parva'', have been discovered in deposi ...

'', which is the youngest known

synziphosurine Synziphosurina is a paraphyletic group of chelicerate arthropods previously thought to be basal horseshoe crabs (Xiphosura). It was later identified as a grade composed of various basal euchelicerates, eventually excluded form the monophyletic Xi ...

'''' and more enigmatic creatures like '' Typhloesus,'' and the ¨Square objects¨ which might be sea slaps or

cnidarians Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that the ...

. Other inverts include, mollusks like the

nautiloid Nautiloids are a group of marine cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded specie ...

'' Tylonautilus,'' pterioid

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

which have been found encrusting ''

sargassum ''Sargassum'' is a genus of brown (class Phaeophyceae) macroalgae ( seaweed) in the order Fucales. Numerous species are distributed throughout the temperate and tropical oceans of the world, where they generally inhabit shallow water and coral ...

'' like brown algae'''' as well as productid

brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, wh ...

, ''Paleolimulus'','''' phyllocarids and

echinoderms An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the ...

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