NEW COCHLIODONTS (CHONDRICHTHYES, HOLOCEPHALI) FROM THE PENNSYLVANIAN OF NEVADA AND ARIZONA

The Bird Spring Formation is a more than 1,000 m thick limestone, with interbedded, fine-grained siliciclastic intervals. It overlies the Monte Cristo Formation (equivalent to the Redwall Limestone) and ranges in age from Late Mississippian to Early Permian. It has a rich invertebrate fauna, however the only vertebrate material previously reported from this formation is an isolated cochliodont tooth found by an amateur collector.

A new specimen from the Bird Spring Formation consists of a lower jaw with complete articulated dentition from a cochliodont provisionally identified as Deltodus sublaevis, otherwise only known from the type locality in Ireland and the Naco Formation of Arizona. Cochliodonts are a group of chondrichthyans with dentition comprising teeth or tooth plates, which are shed infrequently or retained and enlarged throughout life. The dentition always indicates durophagy and is often heterodont. Systematics of the cochliodonts are poorly known as this order of Late Paleozoic fishes consists almost entirely of tooth-based taxa although refinement of tooth-based taxa can still be affected when articulated dentitions are found. This specimen shows three pairs of robust, tightly coiled plates occupying the jaws. The only other articulated cochliodont lower dentition, from C. contortus, does not include the most anterior tooth plates. Wear facets on the tooth plates indicate an upper dentition that was broadly similar in morphology, contrary to the proposed arrangement for C. contortus in which the upper jaw had a posterior pair of large oblong plates succeeded anteriorly by two pairs of whorls of Helodus-like teeth.

Additionally, a new tooth from the same locality has characteristics of the genus Peripristis, which had one upper multicuspid and one lower monocuspid tooth. However, while it is multicuspid and has a broad root like other pristodonts, the root is bifurcated and the cusps consist of two large median cusps and smaller lateral cusps. This clearly indicates that it is a new species, the unique specimen representing an upper tooth. Pristodonts are rare and Peripristis is only known from mid-continent and eastern USA. However, an undescribed peripristid is also known from the Naco Formation in Arizona. Its uncharacteristically very thin crown indicating it also represents a new species.