Chondrichthyans from the Pennsylvanian (Desmoinesian) Naco Formation of central Arizona

Teeth, spines, and dermal denticles of chondrichthyans are reported from the Middle Pennsylvanian (Desmoinesian) Naco Formation of central Arizona. The most common elements are crushing teeth of the cochliodont Deltodus angularis, less common are teeth of D. sublaevis, Venustodus leidyi, Lagarodus angustus, “Cladodus” occidentalis, Petalodus ohioensis, Orodus sp., and Hybodontoidea. Fin spines of Acondylacanthus sp., Amelacanthus sp., and Physonemus sp., and the dermal denticle Petrodus patelliformis are also present. The material of Venustodus leidyi shows for the first time that this animal was heterodont, having arched anterior teeth with a v-shaped profile grading posteriorly into lower crescentic, and finally flattened teeth. Lagarodus angustus is shown to have at least three tooth morphotypes, and a new tooth arrangement is proposed in which small anterior teeth are replaced posteriorly by large crushing teeth arranged in whorls.

This fauna is similar to others in New Mexico, Colorado, and Ohio and constitutes a western extension of such faunas in North America. In addition, the presence of Deltodus sublaevis and Lagarodus angustus documents a range extension from a known European distribution, reinforcing the cosmopolitan nature of chondrichthyan faunas at this time.