New skeleton and associated skull of Homunculus patagonicus Ameghino, 1891 (Primates, Platyrrhini), from the Miocene of Patagonia (Argentina)

Abstract

We describe a new skull and partial skeleton of Homunculus patagonicus Amegh-ino, 1891a, from the Early-Middle Miocene Santa Cruz Formation of Argentinian Patagonia (Santacrucian South American Land Mammal Age, late Early Miocene). All known Santacrucian material fits within a single genus Homunculus, and most of the material in a single species: H. patagonicus. Full consideration of the cranial and dental specimens collected over the past 20 years (representing several individuals) permits a re-evaluation of the paleobiology of Homunculus species. New body mass estimates averaging 2,164 g are produced based on humeral and femoral long-bone cross sections of the new specimen reported here. The new estimate is considered in the context of previous estimates for Homunculus patagonicus. Evaluation of the new and previously described postcranial material leads us to infer that Homunculus was a generalized arboreal quadruped that used pronograde locomotion with flexed elbow and knee joints, pronated forearms, and occasional leaping through a gap-filled canopy; it likely spent much of its time climbing and clinging to large upright supports. The skull reinforces previous inferences that Homunculus ate relatively resistant foods that incorporated or were covered by grit. Based on the new body mass and endocranial volume estimates, we confirm that Homunculus had a relatively small brain compared with most extant platyrrhines. The olfactory bulb of Homunculus widely overlaps with extant anthropoids in relative size.