Takeshi Setoguchi

The fossil record of callitrichine primates

Six out of the 16 recognized species of fossil New World monkeys have been discussed as possible relatives of the modern callitrichines. The dental evidence for these views is examined, with emphasis on the homologies and polarities of the relevant characteristics. We conclude that there is no support for the idea that either Xenothrix or “Saimiri” bernensis are related to callitrichines, thus leaving unconfirmed the interpretation that some subfossil postcrania from the Caribbean pertain to the group. The middle Miocene La Venta forms Micodon and Mohanamico (shown not to be synonymous with Aotus dindensis) appear to be callitrichines: the first, largely on account of its very small size; and the second, by the morphology of the lower canine and canine/premolar complex. Potentially derived features shared by callitrichines and Soriacebus, an older form from Patagonia, are convergent, however. Soriacebus is referred to a new higher taxon of the Tribe Pitheciini (Subfamily Pitheciinae), Subtribe Soriacebina, distinguished from its sister-group, the monophyletic Subtribe Pitheciina, by exhibiting a more primitive morphology than the characteristic sakiuakari dentition. The La Venta Neosaimiri, an alleged intermediate between callitrichines and other platyrrhines, is autapomorphically linked with squirrel monkeys, as is another cebine from the early Miocene, Dolichocebus, once classified as a callitrichine. The fossil record thus indicates that callitrichines were in existence by the middle Miocene, but their rarity as fossils reveals little of their broader phylogenetic ties or adaptive history.

Miocene marmosets: First fossil evidence

The first fossil remains of marmosets, an isolated incisor, premolar, and molar, all similar in size toCallithrix species, have been discovered in the middle Miocene La Venta fauna of Colombia. The M1 is referred to a new genus and species,Micodon kiotensis, characterized by a fully developed hypocone and low occlusal relief. The P4 and I1 resemble those ofCallithrix, suggesting a close affinity with callitrichin marmosets. In combining small size with a four-cusped morphology,Micodon demonstrates the shortcomings of typological definitions of platyrrhine families and suggests that small body size may have preceded the tricuspid molar pattern in marmoset evolution. The 14- to 15-Ma date for the La Venta suggests that marmosets are an at least moderately ancient radiation, contrary to estimates based upon the molecular clock.

Dental variability inSaimiri and the taxonomic status ofNeosaimiri fieldsi, an early squirrel monkey from La Venta, Colombia

Neosaimiri fieldsi, from the South American middle Miocene locality of La Venta, is represented by a relatively complete mandible and dentition that strongly resembles that of extantSaimiri. Comparison with a large sample of mandibles ofSaimiri indicates that this specimen cannot be distinguished from modern populations on the basis of any reportedly diagnostic feature, such as cingulid development, molar length ratio, trigonic/talonid ratio, or mandibular depth. The fossil is best considered an extinct species of the modern genusSaimiri until further material indicates otherwise.

New platyrrhine tali from La Venta, Colombia

Two new primate tali were discovered from the middle Miocene of South America at La Venta, Colombia. IGM-KU 8802 is similar in morphology toCallicebus andAotus, and is allocated to cf.Aotus dindensis, while IGM-KU 8803, associated with a dentition of a new cebine primate, is similar toSaimiri. Both tali differ from the other known fossil platyrrhine tali,Dolichocebus andCebupithecia, and increase our knowledge of the locomotor diversity of the La Venta primate fauna.

Kondous laventicus, a New Ceboid Primate from the Miocene of the La Venta, Colombia, South America

A new genus and species of fossil primate, Kondous laventicus, part of the Miocene La Venta primate fauna of Colombia, South America, is described here for the first time. Screening at a new quarry within the Monkey Unit of the Honda Formation, the Kyoto Site, has revealed dental remains of this new form of a large-sized ceboid. The La Ventan vertebrate fauna is comparable to the Friasian Land Mammal Age, indicating a middle Miocene age. Biostratigraphic studies suggest a 13.6-15.2 Ma for the Friasian faunal zone. Kondous is most closely allied to extant spider monkeys, Ateles, providing the first fossil evidence of their phylogeny. It also implies a nearly three-fold discrepancy between the molecular and paleontological estimates of the age of the Ateles lineage.