Interpretation of anatomical characters in phylogenetic analysis of Pinnipedia, with emphasis on Otariidae (Mammalia, Carnivora)

Resumo

The hypothesis that pinnipeds have a common origin gained support during the 1980s in discussions focused on the systematics of the group. However, the limited knowledge of the anatomy of several species and the frequent variation in several character states make it difficult to clarify the phylogenetic relationships of pinnipeds. Our purpose was to review the anatomical characters of the syncranium and dentition used in phylogenetic analyses by studying the otariids Otaria byronia (n=25) and Arctocephalus australis (n=48). Some interpretations of characters presented in the literature were found to be questionable, notably: (1) shape and position of the premaxillary tuberosity; (2) orientation of the maxillary postcanine alveoli; (3) naso-labialis fossa; (4) shape of the jugal contact with the zygomatic process of temporal; (5) relief and length of the tympanic bone; (6) relationship between the height of the condylar process in relation to the lower postcanine teeth alveoli; (7) individualization of the canal of the cochlear aqueduct and round window; (8) separation of the openings for the cranial nerves VII and VIII in the internal auditory meatus; (9) lingual cingulum on the third upper incisor; (10) development of the metaconid of the fifth upper postcanine tooth, and (11) number of roots in the second to fourth upper postcanine teeth and fifth lower postcanine tooth. These observations indicate the relevance and the need for detailed anatomical descriptions of pinnipeds for understanding their phylogenetic relationships and, consequently, their evolutionary relationships.