Towards an homology-based nomenclature for the cusps of bunodont molars in ungulates.

GELFO J. N.; MERINO, M.L.; GASPARINI, G.M.

Mendoza

Congreso; 10th International Mammalogical Congress Abstracts; 2009

SAREM

Despite the weightiness of molecular data in ungulates phylogenetic analyses, the diversity of extinct groups, only available for their study through the fossil record, demand the use of morphological characters. Teeth are commonly used in diagnosis, due to their large number of characters. Among ungulates, the bunodont molar is not the prevailing type of dentition, but it was present in the stem group of most lineages and, currently, is retained in several specialized omnivorous forms. To search for the phylogenetic relationships between extant and extinct ungulates, the accurate identification of primary homologies of molar cusps is necessary. However the use of different names for homologous cusps, and the same denomination for non homologous one, went against the proper analysis of ungulates phylogenetic relationships, and the pondering of their molar variation. Wild boar (Sus scrofa) a species with an extensive geographic range and ecological tolerance, is well known for their anatomy and physiology. Its tribosphenic pattern is modified and the bunodont structure specialized, cusps are divided by internal folds, and new cusps are added, particularly in m3. This complex pattern derived in a mainly descriptive cusp nomenclature, rather than homology-based one. We discuss a hypothesis on cusp homologies of the m3, which have three large lobes. Our observations led as to the following preliminary conclusions: (1) the more mesial corresponds to the trigonid, where the metaconid and the protoconid are divided each one in four minor portions. (2) the middle lobe corresponds to the talonid which has hypoconid and entoconid divided in four and two portions respectively, and, a low structure with the mayor axis labio-lingual oriented, interpreted as the remnant of the cristid obliqua. The hypoconulid is usually undivided. Finally (3) the distal lobe is homologus to the postcingulid, has at least four large blunt cusps separated by furrows.