Tooth Root Size, Chewing Muscle Leverage, and the Biology of Homunculus patagonicus (Primates), a Monkey from the Miocene of Patagonia.

PERRY J.M.; KAY R.F; VIZCAÍNO S. F.; BARGO M. S.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2010 p. 355 - 371

0002-7014

Until now, inferences about the diet of Miocene platyrrhine monkeys have relied upon the structure of the molar teeth, specifically the development of the crests on the molars. Here, using a library of Micro-CT images of a broad comparative sample of living platyrrhines (callitrichines, cebines, pitheciids and atelids), late early Miocene Homunculus, and the early Miocene taxa Tremacebus and Dolichocebus, we extend these inferences by examining the surface areas of the tooth roots, which serve as anchor points for the periodontal ligament.  We also estimate the leverage of the chewing muscles at bite points from the canine to the last molar, relying on muscle scars preserved on the skull. Extant platyrrhine gougers do not have especially large canine or anterior premolar roots.  The extant platyrrhine folivore, Alouatta fusca, has much larger molar roots than does the similar-sized frugivore Ateles geoffroyi.  Homunculus patagonicus, relative to body size, has larger postcanine roots than any extant platyrrhine in our sample. Homunculus also has poor masticatory leverage compared to the extant platyrrhines studied.  The large postcanine roots, heavy tooth wear, and moderately-long shearing crests suggests a diet of abrasive, resistant foods.  However, relatively poor jaw adductor leverage put the masticatory apparatus of Homunculus at a mechanical disadvantage for producing high bite forces, when compared to the condition in extant platyrrhines. Tremacebus or Dolichocebus, like Homunculus, have larger tooth root surfaces than comparable-sized living platyrrhines. The lack of adequate mandibular material makes observations about masticatory leverage in these taxa less precise but it seems clear that they also resemble Homunculus in having more prognathic faces and posteriorly located temporalis origins - all features of a relatively poor leverage system.