RESUMO

We report here a new fossil primate from the middle Miocene of Argentina. The material consists of isolated teeth, mandibular fragments, and a talus. The fossils were collected in the Collón Cura formation at Cañadón del Tordillo in Neuquén Province. An age of 15.71 +/- 0.07 Ma has been reported for the Pilcaniyeu Ignimbrite, which lies just below the paleosols in which the fossils were found. This material is thus the youngest occurrence of fossil primates in Argentina (hitherto documented in the Santacrucian and older land mammal ages) but still is older than the middle Miocene platyrrhine primates from La Venta, Colombia, in particular the pitheciins Nuciruptor and Cebupithecia. The material is recognized as a new genus and species of Pitheciinae, Propithecia neuquenensis. The mesiodistally compressed, high-crowned incisors are specialized and similar to species in the tribe Pithecini and to the nonpitheciin Soriacebus (early Miocene, Patagonia). We rule out a phylogenetic relationship to the latter because of differences in molar morphology. Propithecia does, however, fit well into the pattern of pitheciin evolution, being more derived than the middle Miocene pitheciin Nuciruptor but not as much as another middle Miocene taxon, Cebupithecia. As such, this makes Propithecia the oldest taxon that can be confidently placed within this modern New World monkey subfamily. By analogy with the molar structures and diets of extant platyrrhines, Propithecia has a molar structure consistent with a variety of low-fiber diets ranging from fruit and gum to seeds. Its incisors suggest seed-eating in much the same way as extant pitheciins, like Pithecia. The talus resembles that of Callicebus, suggesting arboreal quadrupedal locomotion.

Assuntos

RESUMO

A new genus and species of platyrrhine primate, Nuciruptor rubricae, are added to the increasingly diverse primate fauna from the middle Miocene of La Venta, Columbia. This species displays a number of dental and gnathic features indicating that it is related to living and extinct Pitheciinae (extant Callicebus, Pithecia, Chiropotes, Cacajao, and the Colombian middle Miocene Cebupithecia sarmientoi). Nuciruptor is markedly more derived than Callicebus but possesses a less derived mandibular form and incisor-canine complex than extant and extinct pitheciins (Cebupithecia, Pithecia, Chiropotes, and Cacajao), suggesting that it is a primitive member of the tribe Pitheciini within the larger monophyletic Pitheciinae. Nuciruptor has procumbent and moderately elongate lower incisors and low-crowned molars, suggesting that is was a seed predator, as are living pitheciins. Its estimated body size of approximately 2.0 kg places it within the size range of extant pitheciines. The dental and gnathic morphology of Nuciruptor clarifies several aspects of dental character evolution in Pitheciinae and makes it less likely that the enigmatic Mohanamico hershkovitzi (m. Miocene, Columbia) is a pitheciin.

Assuntos

RESUMO

A comparison of the species richness and macroniche composition of diet, locomotor and body-size classes among 16 nonvolant mammalian faunas in tropical South America reveals numerous significant positive correlations with rainfall. In particular, significant and strong positive correlations with rainfall are found in 18 attributes, including the number of nonvolant mammal species, number of primate species, number of frugivores, primary consumers, arborealists, and the number of species between 100 g to 10 kg in body weight. Estimates of annual rainfall derived from least-squares and polynomial regressions and principal components analysis yield a modal estimate of between 1500 and 2000 mm annual rainfall for the Monkey Beds assemblage at La Venta. This level of rainfall is associated today with the transition between savanna and forest environments in lowland equatorial South America. Paleontological evidence strongly suggests the presence of forest biotopes at La Venta. Paleontologic and sedimentologic evidence together indicate a dynamic and heterogeneous riparian mosaic associated with the shifting course of meandering rivers. Faunal evidence also suggests that habitat heterogeneity and canopy discontinuity extended into the interfluvial area. Seasonal rainfall was probably only of secondary importance in shaping the structural and spatial configuration of the dominantly forested mosaic habitat at La Venta. The fossil record is not consistent with the presence of extensive primary or undisturbed, continuous-canopy, evergreen tropical rainforest. The reconstructed middle Miocene environment at La Venta differs significantly from modern environments of similar geography on the piedmont east of the Andes at the same latitude. This in turn suggests that the extensive evergreen rainforests of the upper Amazonian piedmont that today receive more than 4000 mm of rainfall may post-date the initiation of Andean uplift.

Assuntos

RESUMO

A nearly complete but badly crushed skull and mandible of Lagonimico conclucatus, gen. et sp. nov. is described from the La Victoria Formation, Colombia. The specimen is of middle Miocene age and dates from about 13.5 Ma. Features of the dentition suggest Lagonimico is a sister group to living Callitrichinae (Saguinus, Leontopithecus, Callithrix, and Cebuella). These features include having elongate compressed lower incisors, a reduced P2 lingual moiety, and the absence of upper molar hypocones. The new taxon also has autapomorphies, such as a relatively deep jaw, that rule it out of the direct ancestry of any living callitrichine. This animal is assigned to a new tribe of the callitrichine clade. The orbits of L. conclucatus are small, suggesting diurnal habits. Inflated, low-crowned (bunodont) cheek teeth with short, rounded shearing crests, as well as premolar simplification and M3 size reduction, suggest fruit- or gum-eating adaptations, as among many living callitrichines. Procumbent and slightly elongate lower incisors suggest this species could use its front teeth as a gouge, perhaps for harvesting tree gum. Estimates from jaw size suggest Lagonimico weighed about 1,200 g, about the size of Callicebus, the living titi monkey of South America. Judged from tooth size and jaw length, Lagonimico would have been slightly smaller than Callicebus, but still larger than Callimico or any living callitrichine. Therefore, many of the distinctive anatomical features of the callitrichine clade, sometimes explained by phyletic dwarfing, may have evolved at larger body size. Evolutionary size reduction may have occurred in parallel in callitrichines and Callimico.

Assuntos

RESUMO

Distal portions of humeri from two Miocene Colombian primates were recovered during field work in 1986. The larger IGM 183420 is very similar in size and morphology to the humerus included in the type specimen of Cebupithecia sarmientoi, recovered from La Venta in 1945 (Stirton and Savage: Serv. Geol. Nac. Bogata 7:345-356, 1951) and is assigned to this taxon. IGM 183420 presents a number of features of the humerus associated with clinging postural behaviors in living platyrrhines, including a medial epicondyle with very little dorsal angulation, a cylindrical trochlea, and a contact facet for the coronoid process of the ulna. In these and other features Cebupithecia most closely resembles the extant genus Pithecia. IGM 183512 is approximately the size of Saimiri sciureus and is very similar in morphology to the humerus of this small arboreal quadruped. The medial epicondyle is more dorsally angled, the medial lip of the trochlea is more pronounced and the capitulum is less spherical as compared to Cebupithecia. This fossil is assigned to the taxon Neosaimiri fieldsi.

Assuntos

RESUMO

Fossil fishes from the Miocene La Venta fauna of the Magdalena River Valley, Colombia, are identified as Colossoma macropomum (Characidae), a living species from the Orinoco and Amazon basins. The fossils document a long and conservative history for a species that is highly specialized for feeding on streamside plants. The phylogenetically advanced position of Colossoma in the subfamily Serrasalminae implies that six related genera and other higher characid taxa originated well before 15 million years ago. This discovery also corroborates neontological evidence for a vicariance event that contributed species from Miocene Orinoco-Amazon faunas to the original Magdalena region fauna. The fossils suggest a formerly diverse Magdalena fauna that has suffered local extinction, perhaps associated with late Cenozoic tectonism. This new evidence may help explain the depauperate nature of the modern Magdalena River.