Dental anomalies in the atlantic population of south american sea lion, <i>Otaria byronia</i> (Pinnipedia, Otariidae): evolutionary implications and ecological approach

Abstract

We analyzed 63 cases of dental anomalies from 62 specimens of a total sample of 516 specimens of the Atlantic population of South American sea lions, Otaria byronia de Blainville, 1820. The anomalies were represented by 53 cases of missing upper post-canine 6 (second molars), seven cases of maxillary or mandibular extra teeth, two cases of 'dentes geminatis'; and one case of reduced teeth. Considering a phylogenetic framework where all otariid species and basal Pinnipedimorpha are included, missing post-canine 6 could be related to evolutionary trends in Otariidae towards a progressive reduction and loss of teeth (agenesis). The occurrence of the upper post-canine 6 in Otaria Péron, 1816 as in Phocarctos Peters, 1866 is usually regarded as a primitive character. Alternatively, when adopting another cladistic procedure, this could be interpreted as a taxic atavism at the base of Otaria/Phocarctos clade. Extra-mandibular teeth are related to a concrete case of spontaneous atavism in the dentition of Otaria byronia, in retrogression to ancient groups like the Miocene pinnipediform Pteronarctos Barnes, 1989. The other anomalies - maxillary extra teeth, 'dentes geminati'; and reduced teeth - are caused by some disturbance on the epigenetic system underlying dental morphogenesis leading to duplication, coalescence or duplication and reduction of the dental germ, respectively. Dental formula in Otaria byronia shows a high degree of variability and this variability must be considered in the light of their phylogenetic relationships and their evolutionary history. The ecological approach suggests that dental anomalies do not affect longevity, and are unrelated to dietary items or environmental disturbances, but these points need more careful studies.