Dental macro- and micromorphology of a new pitheciid primate from the Miocene of Patagonia.

TEJEDOR, MARCELO; NOVO, NELSON; HOGG, RUSSELL; ROSENBERGER, ALFRED

Portland, Oregon

Jornada; 81St Annual Meeting of the American Association of Physical Anthropologists; 2012

American Association of Physical Anthropologists

Introduction We report a new primate genus fromCerrodelosMonos, oftheearlyMiocenePinturasFormationincentral-westernPatagonia, Argentina.  The holotype for this genus is a left palate with partial dental preservation; there more than a dozen referred specimens, mostly teeth and a few mandibular fragments.Themorphology of the new genusissimilartoCarlocebusandHomunculus, supportingalinktoHomunculinae (including Callicebus), within the Pitheciidae(whichalso includesPitheciinae).  However, thenewtaxonissomewhatlargerandmorebunodont.  The addition of this genus to the record of primates from this region reinforcestheideaofanunexpectedlyhighdiversityofthepitheciidradiationinextra-Amazonian, NeogeneSouthAmerica.  Microscopic analysis of dental enamel also suggests that the diet of this genus was not mechanically demanding, and that complex enamel patterns associated with difficult-to-process foods may not have been a major adaptive feature of the homunculines in general (as opposed to their pitheciine relatives). Site Located in the northwestern portion of Santa Cruz Province, Argentina, the Pinturas formation is situated in the central-western portion of Patagonia (Fig. 1).Pinturas is a complex of pyroclastic and epiclastic sediments (De Barrio et al., 1984; Bown and Larriestra, 1990;Kramarz and Bellosi, 2004) from the early Miocene.  Since the mid-1980s, joint paleontological expeditions of the MuseoArgentino de CienciasNaturales (MACN) and Stony Brook University recovered an abundant collection of vertebrates, mostly mammals.  More recent expeditions organized by MFT (Centro NacionalPatagónico- CONICET, Argentina), and ALR (Brooklyn College, CUNY, U.S.A.) have collected additional primates and other mammals. Few of the mammal specimens are well preserved, and complete bones and skull parts are rare.  The collection is predominantly comprised of fragmentary jaws, maxillae, and isolated teeth.Pinturas has yielded four other named primate species to this point (Soriacebusameghinorum, S. adrianae, Carlocebuscarmenensis and C. intermedius), and therefore contains the most diverse assemblage of primates known in South America after the site at La Venta, Colombia (Hartwig& Meldrum, 2002).All the specimens of the new genus come from the locality of Cerro de los Monos(Fig. 2), within the Pinturas formation (Bown and Larriestra, 1990).  40Ar39Ar datings of upper and lower layers place Cerro de los Monos between 17.7 Ma and 16.5 Ma (Bown and Larriestra, 1990; Fleagle et al., 1995). Morphology Themostcompletespecimenofthenewprimateis the holotype, MACN-SC 100 (MuseoArgentino de CienciasNaturales, Fig. 3),apalatecontainingtheleftI2, P4-M1, M3, rootsoftheleftM2, andoftherightP4-M3.  Fifteenreferreddentalspecimensexist, two of which include fragmentary mandibles.  Molarsandpremolarsarebunodont, withlowocclusalrelief.  Uppermolarsaretransverselybroadandrectangularwithlarge, roundedhypocones (Figs. 3, 4, &5).  Lowermolars(Fig. 6) arebuccolinguallybroad, withtrigonidsthatarebroadandtallerthanthetalonids.  Thecristidobliquidisrelativelyshortinthelowermolars.  Cusps, crestsandcrownsidewallsaresmoothandrounded, withshallowbasins.  Themandibleisrelatively thickatthesymphysis, andnearthealveolarsurface. The new genus differs from Homunculus patagonicus and Carlocebuscarmenensis in the lingual enlargement of P4, and differs from Killikaikeblakei, Homunculus patagonicus, and Carlocebuscarmenensis in having a large M1mesiolingualcingulum, stronger bunodont cusps, and blunt crests rather than being more cristodont with more conical cusps.  It differs from Carlocebuscarmenensis and Homunculus patagonicus in having a shorter entocristid and cristidobliquid on lower molars, buccolingually broader lower molars, and P4 larger with broader lingual side and thicker enamel.  The mandible shows a posterior depth comparable to Homunculus, but is more robust than those of other Patagonian platyrrhines. Scanning Electron Microscopy of broken lower molars (MPM-PV 1810) reveals a simple, radial pattern of enamel prisms (Fig. 7& 8), similar to that seen in extantplatyrrhines such asCallicebus (Fig. 9), Aotus, and Saimiri, as opposed to the complex decussating enamel patterns seen in extant pitheciines such as Pithecia spp. (Nogami and Yoneda, 1983; Martin et al., 2003; Hogg, 2010). Discussion Overall, the gross dental and mandibular characters of the new Pinturas genus most strongly support a link with Homunculinae.Specifically, the bunodont molar morphology, well-developed hypocone, and posteriorly deep mandibular corpus are synapomorphies which the new genus has in common with this particular platyrrhine subfamily.  However, the new genus is a slightly larger, more robust, and more bunodont representative of the group. Although the polarity of enamel complexity as a character in Pitheciidae (as well as Platyrrhini in general) is still unclear (Hogg, 2010), it is still useful for informing interpretations of adaptation.  Given that the dental enamel of the new Pinturas primate resembles that of the extant homunculineCallicebus, there is a suggestion that the dietary regime of homunculines in general did not involve any obvious microanatomical adaptation to particularly hard or tough foods.  While it may be argued that the small size of the new genus is explanation enough for its radial enamel, and that its enamel is therefore not a bearer of useful evolutionary signal, the presence of complex enamel in some even smallerplatyrrhines such as Cebuella suggests otherwise.  Overall, the new Pinturas genus creates a total of three early Miocene homunculine genera from multiple localities ranging between the coast of Patagonia to the west in Santa Cruz province.  Adding in the presence of another homunculine, Miocallicebus, from the middle Miocene at La Venta, Colombia (Takai et al., 2001), and a pitheciine, Soriacebus, from Pinturas (Fleagle&Tejedor, 2002; Tejedor, 2000, 2005; Rosenberger et al., 2009), the sum of the current evidence suggests that the Pitheciidae represent the most important platyrrhine radiation in the Miocene of South America. 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