"Giant" tamarin from the Miocene of Colombia.

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.