73 - Dental Topographic Analysis of Platyrrhine Molars Indicates Dietary Differentiation Occurred During the Middle Miocene

Poster Board Number: 73
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Abstract Body : The extant platyrrhines are a dietarily diverse group containing folivores, frugivores, seed predators, insectivores, and gumnivores. Today, platyrrhines are confined to the tropical regions of Central and South America. However, during the early Miocene their range extended to Patagonia and until the middle Holocene platyrrhines were found in the Caribbean Greater Antilles. Recent fossil discoveries as well as methodological innovations can advance our understanding of the evolution of dietary niche differentiation in this group. Here, we explore when the radiation began to take on its modern level of dietary diversity.

We employ dental shape analysis using a three-dimensional geometric morphometric approach and dental topographic analysis (DTA) using Relief Index, Dirichlet Normal Energy, and Orientation Patch Count-Rotated to explore dietary patterns in the extinct and extant platyrrhines. The sample includes the lower second molars of 17 extinct and 32 extant species of platyrrhines (n=280). Complete dental rows or individual lower second molars were surface scanned; landmarks were placed on scan surfaces using CheckPoint. For DTA, models were downsampled and smoothed in Geomagic Studio, and DTA measures were calculated using the R Package molaR. Discriminant Function Analysis was used to classify primates by diet using DTA values, PC scores, and molar length as a proxy for body mass. Finally, we also used previously published regression equations based on lower molar area and length to create body mass estimates for extinct forms.

The rate of correct classification by diet for extant platyrrhine primates exceeded 90%. Among extinct platyrrhines several interesting dietary patterns emerged: The middle Miocene platyrrhines from La Venta, Colombia had fossil representatives from all modern dietary categories including the earliest instance of folivory in Stirtonia victoriae and of seed predation in Cebupithecia sarmietoi. In addition to having the largest of the Miocene fossil platyrrhines (S. victoriae, 11,000 g), La Venta also had small-bodied platyrrhines (500-600 grams) potentially incorporating insects as a substantial part of the diet. Among the Patagonian forms, dental morphology was more constrained with most forms reconstructed as consuming fruit; however, DTA values fell within the range of seed predators for Carlocebus carmanensis. Body mass for Patagonian primates ranged from 900 grams (Soriacebus adrianae) to 3000 g (Carlocebus carmanensis). The Greater Antillean primates were frugivores as well except for Paralouatta varonai, which is reconstructed as a folivore; their body masses ranged from 4000-8000 g. From these analyses, it is apparent that platyrrhines were acquiring modern degrees of dietary niche differentiation by the middle Miocene. The range of dietary niches open to early Miocene Patagonian primates may have been constrained by the more seasonal environment. Caribbean primates also lack the dietary diversity of mainland forms potentially a result of niche availability on the islands as well as the history of limited species dispersal. Overall, it is apparent that by the middle Miocene, platyrrhine primates had acquired modern levels of dietary diversity in the context of the proto-Amazonian Basin.