HETEROCHRONY AND DENTAL ONTOGENETIC DIVERSITY IN METATHERIAN MAMMALS: CIRCUMVENTION OF CONSTRAINTS IN SOUTH AMERICAN EXTINCT PREDATORS (SPARASSODONTA)

FORASIEPI, A.M.; SANCHEZ-VILLAGRA M.

Barcelona

Congreso; 10th International Congress of Vertebrate Morphology; 2013

Tooth replacement in Metatheria is restricted to a single element, the DP3/dp3, and across the group the timing of dental eruption is variable. We analyzed the sequence of eruption of 77 specimens of marsupials and fossil metatherians, including the Sparassodonta, an extinct basal clade of specialized carnivores. They have patterns that are unique and contrary to otherwise universal patterns. (1) The upper and lower homologous molars erupt more in parallel in sparassodonts, unlike other metatherians where the lower molars precede the homologous upper elements. (2) Sparassodonts show the P3/p3 erupting together, in common with some didelphids. In other didelphids p3 precedes P3, while in the remaining didelphids, some peramelids, one caenolestid, and Pucadelphys, this order is reverse. (3) The canines of larger sparassodonts appear to complete their eruption at the end or after the eruption of the complete adult dentition. Furthermore, the upper canine in thylacosmilids and proborhyaenids are hypsodont and the lower canine in proborhyaenids is semihypsodont. (4) Sparassodonts have different morphologies for the DP3/dp3, suggesting different diets in the juveniles. (5) Deciduous teeth are functional for a long period of time, which extends to thylacosmilids retaining a functional DP3 in the permanent dentition. Dasyuromorphia counterparts have a vestigial and non-functional DP3/dp3. The retention of the DP3 and the hypsodont upper canine of thylacosmilids are examples of heterochronic shifts. In metatherians, during ontogeny all molars function as a carnassial pair until the eruption of the M3/m4, the most specialized pair, constraining the teeth to evolve into different shapes. The timing of dental eruption and deciduous morphology are alternative mechanisms to add variability to the dentition of the specialized sparassodonts. Phorusrhacidae birds, Sebecidae crocodiles and Madtsoiidae snakes were contemporaneous predators in the South American ecosystems. It has to be tested their effect in placing constraints upon the sparassodont adaptative zone.