New Mexico Geological Society Annual Spring Meeting — Abstracts

Petalodontiform chondrichthyans are very common in the marine Carboniferous and Lower Permian deposits of many regions, especially the USA. They are known mainly by isolated teeth, except for Janassa, Belantsea, Netsepoye and Siksika. Two teeth of Petalodus have been recovered in the Upper Pennsylvanian (Missourian-NMMNH locality 6939) and Lower Permian (Wolfcampian: NMMNH locality 6938) strata of the Horquilla Formation in the Big Hatchet Mountains, Hidalgo County, southwestern New Mexico. The complete tooth from locality 6939 has a slightly asymmetrical crown and base. The base is considerably curved labially and thickened in the distal part. The Permian tooth of Petalodus is symmetrical, with a very wellpreserved crown and an incomplete, flattened base. Both teeth are assigned to a group of species that includes P. ohioensis Safford and P. acuminatus Agassiz. The teeth of P. acuminatus differ from those of P. ohioensis in the wide, lingually-ridged band according to Hansen (1997), and in smaller tooth size and equally short crown and base according to Zidek and Kietzke (1993). However, the lingual band of P. ohioensis teeth described by various authors from different localities displays a large variation in width. Such differences could be explained by the position of the teeth in the heterodontous dentition of one Petalodus species. Probably, a detailed redescription of Safford and Agassiz’s type collections will allow recognition of or synonymy of those species. The crown preservation of the Permian tooth from the Big Hatchet Mountains allows us to suggest a new reconstruction of tooth occlusion in the Petalodus dentition with the overlapping of crowns of the teeth from the upper and lower jaws.