Xenothrix and ceboid phylogeny

The known morphology of the subfossil Jamaican primate, Xenothrix mcgregori, is described and systematically analyzed. A provisional phylogeny of living ceboid genera, based upon eladistie interpretation of available data, is presented. Xenothrix shares derived character states with a monophyletic group of cebids which excludes the genera Cebus and Saimiri. Loss of M 3 in Xenothrix occurred convergently to two-molared callithrieids. In view of the great adaptive diversity of the living Ceboidea, and the probable phyletic affinities of the subfossil to an internally diverse, monphyletic group currently classified within Cebidae, separate familiaI status for Xenothrix is unwarranted. Until a ~ecure, falsifiable phylogeny of ceboids is worked out the designation of new higher taxa is undesirable. Xenothrix rncgregori Williams & Koopman, 1952 is known from a single partial mandible containing two left molar teeth. The specimen was recovered in 1920 by H. E. Anthony from beneath a kitchen midden on the island of Jamaica which yielded other vertebrates thought to be of Pleistocene or Recent age. Several of the numerous postcranials coming from the same site are possibly primate but Williams & Koop/nan judiciously refrained from designating these as paratype. 'Fhere are, of course, no living non-human primates native to Jamaica or the entire West Indian subregion (Hershkovitz, 1972). A single distal tibia, designated Cercopithecus? sp. ? (sic) by Miller (1929), is known, however, from a Dominican Republic deposit associated with an indegenous, partially extinct fauna (Williams & Koopman, 1952). In their initial study of the genus, Williams & Koopman (1952) allocated Xenothrix to Cebidae. Simpson (1956) and Hill (1962) accepted this assignment but Romer (1971) did so only with a query. Simpson later (1969) sunk all living and fossil ceboids into a single family, Cebidae. Recently, Hershkovitz (1970) proposed that a new family, Xenothricidae, be erected to receive this single specimen. The new ranking was adopted in the classifications of Simons (I972) and Hoffstetter (1974). This paper is an attempt to clarify the phyletic affinities of Xenothrix mcgregori. This can be done only within a phylogenetic framework that treats at least all extant ceboid genera. I therefore present a provisional phylogeny of living Ceboidea. Although my major concern here is not classification, it is important to recognize that most classifications, regardless of how they are formulated, are based upon hypotheses of evolutionary relationships. To my knowledge no clear evidence bearing on the affinities of Xenothrix has yet been presented, rendering the evolutionary meaning of the classifications of other authors somewhat ambiguous. I hope to demonstrate that there is in fact no current need to recognize a novel family-rank taxon in order to describe the biological significance of Xenothrix; phyletically and adaptively it cart nest comfortably within a bifamilial (perhaps unifamilial) Ceboidea. In developing the phylogeny presented below, careful attention has been paid to delimiting presumed, strictly monophyletic sets of taxa defined by their mutual possession