Echinochimaera is an extinct genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, it was assigned to the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 chimaera by Jack Sepkoski
Jack Sepkoski
J. John Sepkoski Jr., , was a University of Chicago paleontologist. Sepkoski studied the fossil record and the diversity of life on Earth. Sepkoski and David Raup contributed to the knowledge of extinction events...

 in 2002. The genus' name derives from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 εχινό (echino) meaning spiny, and chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...



The two known Echinochimaera species lived in the Upper Mississippian (Serpukhovian
The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from 328.3 Ma tot 318.1 Ma...

). Fossils of the species were found in the Bear Gulch Limestone
Bear Gulch Limestone
The Bear Gulch Limestone in Montana is a fossiliferous lagerstätte, a limestone layer laid down in the Mississippian epoch of the Carboniferous period, about 318 mya. This lens of limestone was laid down in a surrounding matrix that indicates a landscape of mudflats and braided channels in fresh...

 in Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...


Both species have rounded bodies and paddle-like tails as well as large pectoral fins, two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

s and a jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...

 fused to the braincase. The paddle-like tails indicate that E. meltoni was likely not a predator nor a fast swimmer.

Echinochimaera meltoni

E. meltoni was first described by Richard Lund, a Adelphi University
Adelphi University
Adelphi University is a private, nonsectarian university located in Garden City, in Nassau County, New York, United States. It is the oldest institution of higher education on Long Island. For the sixth year, Adelphi University has been named a “Best Buy” in higher education by the Fiske Guide to...

 palaeontologist, in 1977. The fossils found of E. meltoni have shown a great deal of sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

, males being found to have a maximum 150mm body length while the maximum body length found in females was only 70mm (juveniles were 13-20mm). In general, the females only grew to about half the size of the males. Males also had four pairs of spikes which may have been used to defend against predators and to identify the fish as male.

There was a relative abundance of immature male fossils found, and that together with the significant sexual dimorphism indicate there was extreme sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...

among the species.

Echinochimaera snyderi

E. snyderi was described, like E. meltoni, by Richard Lund. It was described in 1988 based on juvenile specimens, all with a body length under 90mm. E. snyderi differs from E. meltoni in fin detail as well as jaw shape and teeth near the front edge of the face rather than a tooth plate, in mature specimens later found its mature size was found to be larger than E. meltoni.
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