Tremacebus

Abstract: . Inferences about the diet of Miocene platyrrhine monkeys have relied upon the morphology of the molar teeth, specifically the crests on the molars. 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 Tremacebus and Dolichocebus, we extend these inferences by examining the surface areas of the tooth roots, anchor points for the periodontal ligaments. From muscle scars on the skull, we estimate the mechanical leverage of the chewing muscles at bite points from the canine to the last molar. Extant platyrrhines that gouge bark to obtain exudates do not have especially large canine roots or anterior premolar roots compared with their less specialized close relatives. Extant platyrrhines that have more folivorous diets have much larger molar roots than do similar-sized more frugivorous species. Homunculus patagonicus has large postcanine roots relative to body siz...

Abstract: The platyrrhine Homunculus harringtoni Rusconi, 1933, of the Patagonian Late Oligocene, known from a skull fragment, is designated type of new genus Tremacebus, new subfamily Tremacebinae, family Cebidae. Comparisons are made with contemporaneous Dolichocebus Kraglievich, early Miocene Homunculus, and Recent platyrrhines, mainly AotusCallicebus, and Saimiri. Notable characters of Tremacebus include Callicebus-size skull with short face, braincase steeply vaulted, posterior occipital plate and foramen magnum directed more nearly backward than downward, orbits oriented fronto-laterally, interorbital region wide, muzzle broad, zygomatic arch relatively long, dental arch more nearly U- than V-shaped, occlusal surface of dental row moderately curved. Outstanding is the extremely large orbitotemporal opening (basis for generic name) which resolves one of two main cranial characters separating platyrrhines from tarsioids. The two halves of missing Tremacebus mandible are presumably synostosed at symphysis menti as in all platyrrhines, but in no tarsioid. Morphological stages and grades in evolution of primate postorbital closure are described and figured. Platyrrhine origin, history, and relationship are briefly discussed within the framework of continental drift. The Homunculidae are defined and a systematic arrangement is proposed for all New World primate families and genera known from Mexico southward.

Abstract: New primate fossils have been recovered from the late Oligocene (Colhuehuapian) localities of Gaiman and Sacanana in Patagonian Argentina. The new fossils are provisionally allocated to Dolichocebus gaimanensis and Tremacebus harringtoni, the only primates previously described from these localities. These new dental remains are more primitive than the teeth of any previously known platyrrhines, living or fossil, and conform extremely well with the hypothetical ancestral morphotype for New World monkeys suggested by several authors. They are also very similar to the teeth of Oligocene catarrhines from Egypt such as Aegyptopithecus zeuxis.