TYPE SPECIMENS OF THE SARCOPTERYGIAN FISHES ONYCHODUS SIGMOIDES AND ONYCHODUS HOPKINSI FROM THE DEVONIAN OF OHIO REDISCOVERED

Onychodus is one of the best-known sarcopterygian (lobe-fin) fishes. J.S. Newberry (1857) described two species from the “Corniferous limestone” (Columbus-Delaware Limestone; Lower-Middle Devonian) of Ohio. They are O. sigmoides, the type species, based on parasymphysial tusks (teeth) Newberry illustrated in 1853, and O. hopkinsi, based on a parasymphysial whorl with 7 tusks. Newberry (1873) stated that his inclusion of O. hopkinsi in the “Corniferous limestone” fauna was a mistake, and recognized O. hopkinsi as occurring only in the “Chemung” (Upper Devonian) of New York. The repository of the type specimens was not disclosed, and the specimens have been long assumed to be lost.

In 2023-2024, as Ohio Wesleyan University’s Geology Museum collection was being moved to the Orton Geological Museum, type and other specimens of various Devonian fishes studied by Newberry were rediscovered. The collection includes the type material of O. sigmoides and O. hopkinsi, and this prompts a reevaluation of the systematics of these two species. Study of the syntypes of O. sigmoides and the holotype of O. hopkinsi suggest that the parasymphysial tusks of O. hopkinsi differ little from those of O. sigmoides except in characters that track with size and location on the parasymphysial whorl. Parasymphysial tusks from Newberry’s original collection show distinct patterns in the degree of arc, and the extent of distal recurvature. Tusks tend to become sigmoidal (less arcuate and more recurved) with increasing length. Recurvature increases not only according to length, but in some cases also according to position on the parasymphysial whorl; distal tusks are more recurved than proximal tusks in some specimens.

The large tusks assigned by Newberry to O. sigmoides are less arcuate and more recurved distally than the tusks in the relatively small holotype of O. hopkinsi. Onychodus hopkinsi shows arcuate, slightly recurved tusks distally and nearly unrecurved tusks proximally. A relatively large, parasymphysial whorl from the “Chemung” of New York studied by Newberry, which has 5 tusks, differs from the “Corniferous limestone” material: it has arcuate tusks, with subtle recurvature at the distal tips. The specimen closely resembles Onychodus ortoni from the Huron Member of the Ohio Shale (Upper Devonian) of Ohio.