DENTAL ERUPTION AND DECIDUOUS MORPHOLOGY IN SPARASSODONTA (MAMMALIA, METATHERIA): ONTOGENETIC AND EVOLUTIONARY PATTERNS

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

Zapala-El Chocón

Jornada; XXVIII Jornadas Argentinas de Paleontología de Vertebrados; 2014

In metatherians ?marsupials and extinct relatives? only the last premolar is replaced, but the timing of dental eruption is variable within the group. We analyzed the sequence of eruption of 76 metatherian specimens, including Sparassodonta, an extinct clade of specialized carnivores from South America. Most sparassodonts were hypercarnivorous with limited disparity in molar morphology. Some patterns in Sparassodonta seem to be derived in the context of metatherian phylogeny. (1) The P3/p3 erupt in synchrony (in common with some didelphids); (2) the equivalent upper and lower molar loci erupt in closer synchrony than in other carnivorous metatherians, in which the lower molars clearly precede the equivalent upper elements; (3) the upper canines in thylacosmilids and proborhyaenids are hypselodont; and (4) DP3 in thylacosmilids is retained in adulthood. Sparassodonts also have some ancestral patterns recorded in stem marsupials and some crown marsupials. (1) The P3/p3 erupt in closer synchrony with M4/m4; (2) P3 completes eruption before M4; and (3) deciduous teeth have a complex molariform morphology and are functional in the juvenile for an extended period of time. In addition, different sparassodont taxa have different morphologies for the DP3/dp3, suggesting different diets in the juveniles. The specializations in the timing of dental eruption and in the deciduous morphology are evolutionary mechanisms that increase morphological disparity in the group. This is clearly evident from the heterochronic shifts of thylacosmilids (i.e., retention of the DP3 and hypselodont upper canines), in contrast to the otherwise narrow morphospace occupation of Sparassodonta.