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 geminati" 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.Resumo -Foram analisadas 63 anomalias dentárias em 62 espécimes de uma amostra total de 516 indivíduos da população Atlântica do leão marinho sul-americano Otaria byronia de Blainville, 1820. As anomalias foram representadas por 53 casos de pós-caninos 6 (segundos molares) ausentes, sete casos de dentes extranumerários maxilares/mandibulares, dois casos de dentes geminados, e um caso de dente reduzido. Considerando um contexto filogenético onde são incluídas todas as espécies de otarídeos e também Pinnipedimorpha basais, a ausência do pós-canino 6 pode estar relacionada às tendências evolutivas de redução e perda desse dente (agênese). A ocorrência dos sextos pós-caninos superiores em Otaria Perón, 1816 e em Phocarctos Peters, 1866 é, usualmente, considerada um caráter primitivo. Alternativamente, adotando-se um procedimento cladístico distinto, isto poderia ser interpretado como um atavismo táxico na base do clado Otaria/Phocarctos. Dentes extranumerários mandibulares são considerados casos concretos de atavismos espontâneos na dentição de Otaria byronia, em retrogressão a grupos ancestrais como o pinipedimorfo do Mioceno Pteronarctos Barnes, 1989. As outras anomalias -dente extranumerário maxilar, dente geminado e dente reduzido -são causadas por algum distúrbio no sis...

Numerical anomalies in the dentition of southern fur seals and sea lions (Pinnipedia: Otariidae)

“…Maxillary supernumerary teeth have been described in Otariid species in different positions (MILES & GRIGSON 1990, DREHMER & FERIGOLO 1996, DREHMER et al 2004, ABBOTT & VERSTRAETE 2005. As no pinniped ancestor has more than four pre-molars and two molars, totalizing the six post-canine teeth (DREHMER et al 2004), the appearance of maxillary supernumerary teeth in A. tropicalis also does not seem to have any evolutionary or phylogenetic implication.…”

“…DREHMER et al (2004) reported supernumerary teeth in mandibular PC/6, which represents the atavic reappearance of the lower second molar in some specimens of O. flavescens, reconstructing the origins of Pinnipedimorpha evolution in the Oligo/Miocene (BERTA & WYSS 1994, DREHMER et al 2004. The simultaneous occurrence of two supernumerary teeth between the mandibular PC/4 and PC/5 in A. australis and of one supernumerary between PC/3 and 4 in A. tropicalis seems to be unrelated with atavism.…”

“…As no pinniped ancestor has more than four pre-molars and two molars, totalizing the six post-canine teeth (DREHMER et al 2004), the appearance of maxillary supernumerary teeth in A. tropicalis also does not seem to have any evolutionary or phylogenetic implication.…”

“…Supernumerary teeth in Otariids possibly represent a reversion to the primitive dentition of terrestrial carnivores, according to the phylogenetic relationships of Pinnipeds (DREHMER & FERIGOLO 1996, DREHMER et al 2004, CRUWYS & FRIDAY 2006. DREHMER et al (2004) reported supernumerary teeth in mandibular PC/6, which represents the atavic reappearance of the lower second molar in some specimens of O. flavescens, reconstructing the origins of Pinnipedimorpha evolution in the Oligo/Miocene (BERTA & WYSS 1994, DREHMER et al 2004.…”

“…Dental agenesis in South American Otariids has already been investigated in A. australis and A. tropicalis and in O. flavescens (MILES & GRIGSON 1990, DREHMER & FERIGOLO 1996, DREHMER et al 2004. According to the authors concerned, the absence of teeth, particularly of the most posterior ones such as PC/5 and PC/6, represents a trend towards reduction of the postcanine teeth in Otariids.…”