title: The Hand of Cercopithecoides williamsi (Mammalia, Primates): Earliest Evidence for Thumb Reduction among Colobine Monkeys.
abstract: Thumb reduction is among the most important features distinguishing the African and Asian colobines from each other and from other Old World monkeys. In this study we demonstrate that the partial skeleton KNM-ER 4420 from Koobi Fora, Kenya, dated to 1.9 Ma and assigned to the Plio-Pleistocene colobine species Cercopithecoides williamsi, shows marked reduction of its first metacarpal relative to the medial metacarpals. Thus, KNM-ER 4420 is the first documented occurrence of cercopithecid pollical reduction in the fossil record. In the size of its first metacarpal relative to the medial metacarpals, C. williamsi is similar to extant African colobines, but different from cercopithecines, extant Asian colobines and the Late Miocene colobines Microcolobus and Mesopithecus. This feature clearly links the genus Cercopithecoides with the extant African colobine clade and makes it the first definitive African colobine in the fossil record. The postcranial adaptations to terrestriality in Cercopithecoides are most likely secondary, while ancestral colobinans (and colobines) were arboreal. Finally, the absence of any evidence for pollical reduction in Mesopithecus implies either independent thumb reduction in African and Asian colobines or multiple colobine dispersal events out of Africa. Based on the available evidence, we consider the first scenario more likely.
authors.affiliation: Department of Anthropology, 1218 University of Oregon, Eugene, Oregon, 97403-1218, United States of America.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Frost
authors.affiliation: Department of Anthropology, Hunter College of the City University of New York, New York, New York, 10065, United States of America; New York Consortium in Evolutionary Primatology, New York, New York, 10024, United States of America; PhD Program in Anthropology, The Graduate Center, City University of New York, New York, New York, 10016, United States of America.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Gilbert
authors.affiliation: New York Consortium in Evolutionary Primatology, New York, New York, 10024, United States of America; PhD Program in Anthropology, The Graduate Center, City University of New York, New York, New York, 10016, United States of America.
authors.forename: Kelsey D
authors.initials: KD
authors.lastname: Pugh
authors.affiliation: Department of Anthropology, 1218 University of Oregon, Eugene, Oregon, 97403-1218, United States of America; Human Subjects Division, University of Washington, Seattle, Washington, 98185, United States of America.
authors.forename: Emily H
authors.initials: EH
authors.lastname: Guthrie
authors.affiliation: New York Consortium in Evolutionary Primatology, New York, New York, 10024, United States of America; PhD Program in Anthropology, The Graduate Center, City University of New York, New York, New York, 10016, United States of America; Department of Vertebrate Paleontology, American Museum of Natural History, New York, New York, 10024, United States of America; Department of Anthropology, Lehman College, City University of New York, Bronx, New York, 10468, United States of America.
authors.forename: Eric
authors.initials: E
authors.lastname: Delson
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001837:Body Weights and Measures; D016673:Colobinae / Q000033:anatomy & histology* / Q000145:classification; D005580:Fossils; D006225:Hand / Q000033:anatomy & histology*; D007630:Kenya; D050279:Metacarpal Bones / Q000033:anatomy & histology; D010163:Paleontology; D025341:Principal Component Analysis; D012044:Regression Analysis