Three newly discovered skulls of Homunculus patagonicus support its position as a stem platyrrhine and establish its diurnal arboreal folivorous habits

KAY, RICHARD FREDERICK; VIZCAÍNO, SERGIO FABIÁN; TAUBER, ADÁN ALEJO; BARGO,MARÍA SUSANA; WILLIAMS, BLYTHE A.; LUNA, CARLOS ALBERTO; COLBERT, MATTHEW W.

Milwaukee, Wisconsin

Congreso; 74th Annual Meeting of the American Association of Physical Anthropologists; 2005

American Association of Physical Anthropologists

Three remarkably well-preserved skulls, a mandible, and the distal two thirds of a humerus of the early Miocene platyrrhine Homunculus were recovered in 2003-2004 from Patagonian Argentina at 52º south latitude. These finds nearly double the number of known early Miocene crania from the SA continent. A phylogenetic analysis of cranial, dental and postcranial characters suggests that Homunculus was a stem platyrrhine, as indicated by the absence of derived characters shared by the clade of extant platyrrhines. For example, Homunculus is more primitive than in living platyrrhines in having well-developed molar hypoconulids, a P4 hypocone, and upper molar paraconules. The skull structure is more primitive in having the catarrhine’ (primitive anthropoid) suture pattern at pterion, an infraorbital foramen positioned posteriorly on the face, and a robust posterior nasal spine. Furthermore, the nuchal plane forms an angle steeply oblique to the Frankfort horizontal. Homunculus was about the size of a cebus monkey - 2-3 kgs. It does not appear to have been sexually dimorphic. CT-scans reveal an endocranial volume (brain) that is relatively small for a platyrrhine. A small olfactory fossa (and olfactory bulbs) and small orbits with enlarged optic canals suggest diurnal habits and an anthropoid-like level of visual acuity. Molar shearing is well developed, suggesting a mixed folivorous/frugivorous diet. The femur (described previously) is unusual (and primitive for a platyrrhine) in having a deep and narrow knee joint and suggests that leaping played a significant role in the locomotor repertoire. The morphology of the humerus suggests that Homunculus was adept at above-branch quadrupedalism. Support from NSF grant BCS-009025