Anthropoid primates other than humans show a conspicuously disjunct geographic distribution today, inhabiting mostly tropical and subtropical parts of Asia, Africa, and Central and South America. During the latter part of the Eocene, early anthropoids showed a similarly disjunct distribution, although South America and Africa were both island continents then. Attempts to explain the historical biogeography of anthropoids as resulting from vicariance caused by tectonic rifting between South America and Africa conflict with both the chronology and the topology of anthropoid evolution. The only viable hypotheses that remain entail sweepstakes dispersal across marine barriers by early monkeys on natural rafts. Early anthropoids and certain Asian rodent clades seem to have been especially adept at accomplishing sweepstakes dispersal, particularly during the Eocene, although this process has classically been envisioned as highly random and extremely rare. This article identifies and discusses biological and geological factors that make sweepstakes dispersal by certain taxa at given times far less random than previously conceived.
Previously, we described several features of the carpometacarpal joints in extant large-bodied apes that are likely adaptations to the functional demands of vertical climbing and suspension. We observed that all hominids, including modern humans and the 4.4 million-year-old hominid Ardipithecus ramidus, lacked these features. Here, we assess the uniqueness of these features in a large sample of monkey, ape, and human hands. These new data provide additional insights into the functional adaptations and evolution of the anthropoid hand. Our survey highlights a series of anatomical adaptations that restrict motion between the second and third metacarpals (MC2, MC3) and their associated carpals in extant apes, achieved via joint reorganization and novel energy dissipation mechanisms. Their hamate-MC4 and -MC5 joint surface morphologies suggest limited mobility, at least in Pan. Gibbons and spider monkeys have several characters (angled MC3, complex capitate-MC3 joint topography, variably present capitate-MC3 ligaments), that suggest functional convergence in response to suspensory locomotion. Baboons have carpometacarpal morphology suggesting flexion/extension at these joints beyond that observed in most other Old World monkeys, probably as an energy dissipating mechanism minimizing collision forces during terrestrial locomotion. All hominids lack these specializations of the extant great apes, suggesting that vertical climbing was never a central feature of our ancestral locomotor repertoire. Furthermore, the reinforced carpo-metacarpus of vertically climbing African apes was likely appropriated for knuckle-walking in concert with other novel potential energy dissipating mechanisms. The most parsimonious explanation of the structural similarity of these carpo-metacarpal specializations in great apes is that they evolved independently. This article is protected by copyright. All rights reserved.
Selby, Michael S.; Simpson, Scott W.; and Lovejoy, Owen C., "The functional anatomy of the carpo-metacarpal complex in anthropoids and its implications for the evolution of the hominoid hand" (2016). PCOM Scholarly Papers. 1651. _papers/1651 041b061a72