Generalized quadrupeds, committed bipeds, and the shift to open habitats : an evolutionary model of hominid divergence. American Museum novitates ; no. 3250

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New York, NY : American Museum of Natural History
"Proposed models of hominid divergence and the currently accepted hominoid phylogeny fail to account for the distinguishing human characters that led anatomists to hypothesize a prepongid or prehominoid divergence of hominids. Because humans share a cautious climbing ancestry with other hominoids, similarities in the anatomy and proportions of the human musculoskeletal structure with those of gorillas and cursorial cercopithecids suggest that hominids underwent selection for terrestrial quadrupedality after their divergence from a common semiarboreal hominoid ancestor. Selection for terrestrial quadrupedality explains generalized monkeylike characters in humans, reconciling anatomical evidence with the currently accepted hominoid phylogeny. By emphasizing limb movements in the sagittal plane and limb elongation, terrestrial quadrupedalism preadapts an arboreal cautious climber to habitual bipedality. Ecological models based on cercopithecine analogies indicate that at least two adaptive stages prior to the elaboration of human material culture must have occurred if hominid divergence progressed from a semiarboreal life-style in a forest or woodland habitat to a committed terrestrial life-style in an open-country habitat. Based on a baboon model, the initial stage consisted of a generalized, widely distributed woodland ape. Predominantly quadrupedal, this ancestor utilized a wide range of behaviors to exploit a wide range of habitats and food resources. Analogous to gelada baboons, the second-stage hominids exhibited a commitment to open habitats while sacrificing generalized behaviors. The fossil evidence for hominid evolution closely fits this postulated model of hominid divergence. With decreasing geologic age, hominid fossils show an increasingly specialized structure and commitment to open habitats. The presence of (1) more than one hominid lineage committed to open habitats, (2) the likelihood of hybrids between different lineages, and (3) a discontinuous and fragmentary fossil record confound fossil phylogenies and the identification of ancestral hominids"--P. 2.
78 p. : ill. ; 26 cm.
Includes bibliographical references (p. 55-78).