New Mexico Geological Society Annual Spring Meeting — Abstracts

Pycnodonts are extinct neopterygian fishes that lived from the Late Triassic through the middle Eocene, spanning approximately 175 million years where they became particularly diversified during the Jurassic. Over 650 pycnodont species have been described, but 70 percent are known only by their dental remains (e.g., isolated teeth and tooth plates) that are largely characterized by heterodontous crushing teeth.

Isolated teeth from the Juana Lopez Member of the Mancos Shale at Mesa Prieta (NMMNH locality L5999) represent a new species of a large pycnodont. Vomerine teeth of this new taxon are large, domeshaped, and robust, generally with two parallel to subparallel apical ridges that tend to run transversely and may be connected at their middle. They resemble the teeth of “Coelodus” streckeri described from the Turonian of Kansas, which has different apical ridge morphology. Comparison with other more complete pycnodont fossils suggests that the new New Mexican species is one of the largest pycnodonts, likely exceeded 1 m total length (TL) and possibly as much as about 1.2 m TL. Based on its large size and distinctive crushing-type teeth, it is interpreted to be a durophagous fish.

The teeth were recovered from exposures of the shale interval between the upper and lower calcarenite beds of the Juana Lopez Member. These deposits also yield the ammonite Prionocyclus macombi, a distinctive index taxon that defines the P. macombi Zone. This ammonite zone is within the middle or upper Turonian. Although the Juana Lopez Member is rich in bioclastic debris and has been termed a “fish-tooth conglomerate,” this is the first documentation of a pycnodont from this unit in New Mexico. The Juana Lopez Member is also rich in shelled macroinvertebrates, including the oyster Lopha lugubris, an unidentified inoceramid bivalve, and the ammonite Coilopocerascolleti. NMMNH Locality 5999 yields abundant isolated teeth of durophagous shark Ptychodus whipplei and occasionally teeth of piscivorous-type sharks such as Squalicorax cf. S. falcatus and Cretodus sp. New Mexico, like other middle to late Turonian faunas of the Western Interior Seaway, was probably dominated by durophagous fishes that presumably affected the benthic macroinvertebrate community.