Trionyx, Forskal, 1775

Robert & Weems, E., 2014, Paleogene chelonians from Maryland and Virginia, PaleoBios 31 (1), pp. 1-32 : 11

“ Trionyx ” pennatus Cope 1869a

( Fig. 8O)

Specimen —CMM-V-3283, third left costal found by William Counterman.

Locality, horizon, and age — This costal was found in the bluffs north of Popes Creek and south of the Loyola Retreat in southern Charles County, Maryland.The specimen came from the upper part (B) of the Woodstock Member, Nanjemoy Formation; early Eocene (Ypresian, NP 13) .

Description —Costal elongate with no indication of sulcal grooves or any sutural border at its distal end for attachment to a peripheral element. Dorsal surface bears a coarse sculpture of pits and grooves, with pits predominating proximally and grooves predominating distally. Distal rib end protrudes beyond the costal only a short distance.

Remarks —The size, thickness, and external surface sculpture of this specimen are indistinguishable from material described by Cope (1869a) as “ Trionyx ” pennatus, which apparently came from the age-equivalent early Eocene Manasquan Formation in New Jersey. The type material from New Jersey, the specimen described here, and similar early Eocene material described from the Fisher/Sullivan site in Stafford County, Virginia ( Weems 1999) almost certainly pertain to one and the same taxon because all of this material is very similar and also because no other early Eocene species of trionychid turtle has been reported from anywhere in the eastern United States. Although Trionyx Forskål 1775 was once widely used as a generic designation for American Cenozoic soft-shell turtle specimens, the name does not properly apply to any American material ( Meylan 1987). At the same time, however, there are no characteristics preserved in this Nanjemoy material that could clearly establish what the correct generic designation is or even to which subfamily of trionychids it pertains. It is possible, but far from certain, that it pertains to the living genus Apalone Rafinesque 1832 . For now, the established name “ Trionyx ” pennatus is retained with Trionyx in quotes for nomenclatural stability, while recognizing that the type material is not diagnosable and this species is a nomen dubium.