Echinochimaera

The two known Echinochimaera species lived in the Upper Mississippian (Serpukhovian).[3] Fossils of the species were found in the Bear Gulch Limestone in Montana, United States.

Both species have rounded bodies and paddle-like tails as well as large pectoral fins, two dorsal fins and a jaw fused to the braincase.[4] The paddle-like tails indicate that E. meltoni was likely not a predator nor a fast swimmer.[5][6]

Specimen of Echinochimaera meltoni

E. meltoni was first described by Richard Lund, an Adelphi University palaeontologist,[7] in 1977.[1][3] The fossils found of E. meltoni have shown a great deal of sexual dimorphism, 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.[5] Males also had four pairs of spikes which may have been used to defend against predators and to identify the fish as male.[6]

There was a relative abundance of immature male fossils found, and that together with the significant sexual dimorphism indicate there was extreme sexual selection among the species.[5]

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.[8]