Abstract
Comparisons of a moderately worn pmsub4/sub in its jaw, and an isolated dpmsub4/sub of the Oligocene-Miocene Homunculus (the second tooth originally described as that of a marsupial), indicate cebid identity with affinities nearest Alouatta. Diagnoses of dpmsub4/sub, pmsub4 /suband msub1/sub of all known platyrrhines and comparisons with teeth of strepsirhines and tarsioids reveal that platyrrhines cannot be derived from any known non-platyrrhine stock. Speculations on platyrrhine ancestry are reviewed.