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Major transformations in the skull and masticatory system characterized the evolution of crown anthropoids. To offer further insight into the phylogenetic and arguably adaptive significance of specific primate mandibular loading and kinematic patterns, allometric analyses of metric parameters linked to masticatory function are performed within and between 47 strepsirhine and 45 recent anthropoid species. When possible, basal anthropoids are considered. These results are subsequently integrated with prior experimental and morphological work on primate skull form. As compared to strepsirhines, crown anthropoids have a vertically longer ascending ramus linked to a glenoid and condyle positioned relatively higher above the occlusal plane. Interestingly, anthropoids and strepsirhines do not exhibit different mean ratios of condylar to glenoid height, which suggests that both clades are similar in their ability to evenly distribute occlusal contacts and perhaps forces along the postcanine teeth. Thus, given the considerable suborder differences in the scaling of both glenoid and condylar height, we argue that much of this variation in jaw-joint height is linked to suborder differences in relative facial height due in turn to increased encephalization, basicranial flexion, and facial kyphosis in anthropoids. Due to a more elongate ascending ramus, anthropoids evince more vertically oriented masseters than like-sized strepsirhines. Having a relatively longer ramus and a more medially displaced lateral pterygoid plate, crown anthropoids exhibit medial pterygoids oriented similar to those of strepsirhines, but with a variably longer lever arm. As anthropoid masseters are less advantageously placed to effect transverse movements/forces, we argue that balancing-side deep-masseter activity underlying a wishboning loading regime serves to increase, or at least maintain, transverse levels of jaw movement and occlusal force at the end of the masticatory power stroke. Crown anthropoids are also more isognathic and isodontic than strepsirhines. A consideration of early anthropoids suggests that the crown anthropoid masticatory pattern, i.e., more vertical masseters due to a high condyle as well as greater isognathy and isodonty, occurred stepwise during stem anthropoid evolution. This appears to correspond to a more transverse, and perhaps progressively larger, power stroke across oligopithecids, parapithecids, and propliopithecids.

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Recent hyracoids and elephants share a taxeopode arrangement of tarsal and carpal bones, a condition in which bones are aligned with minimal interlocking between adjacent elements. Taxeopody has often been interpreted as a synapomorphy reflecting a close phyletic link between Hyracoidea and Proboscidea, but recently it has been suggested [Fischer, M. S. (1986) Cour.,Forschungsinst. Senckenberg 84, 1-132] that hyracoid taxeopody is an independent acquisition resulting from selection favoring increased midcarpal and midtarsal rotation and that Hyracoidea is actually allied with Perissodactyla. As a test of this hypothesis, isolated carpal and tarsal bones of primitive Oligocene hyracoids from the Fayum, Egypt, have been examined to determine whether these indicate a taxeopode or diplarthral carpus and tarsus. Four complete astragali from the Fayum, representing at least three taxa, show a single, slightly convex articular surface on the head for articulation with the navicular and lack a facet for the cuboid. Two complete magna representing two species have a single proximal facet for articulation with the lunar, and they lack a facet for the scaphoid. Thus, both the carpus and tarsus of Fayum hyracoids are taxeopode. Taxeopody in hyracoids cannot be attributed to selection for carpal and tarsal rotation in climbers because the Oligocene, Miocene, and Recent species show great diversity in body size and probably locomotor specializations, despite relative uniformity of structure in the carpus and tarsus. The shared taxeopody of hyracoids and proboscideans, along with other osteological characters and similarities in hemoglobin, eye lens proteins, and other molecules, all suggest that Hyracoidea belongs within Paenungulata.Modern hyraxes (family Procaviidae) have a taxeopode, or serial, arrangement of the carpal and tarsal bones (1-4). In this arrangement, podial elements are aligned proximodistally with minimal interlocking between the proximal and distal rows of elements, thus providing relatively smooth and uninterrupted midtarsal and midcarpal joints, as illustrated elsewhere (1,3,4). In the carpus, taxeopody is especially evident in the proximal magnum and the distal lunar, which fit together by a single, flat articular surface and do not interlock with medial and lateral elements (although the slightly broader lunar may contact the centrale and unciform, especially during rotation). Similarly, in the tarsus, the distal articulation of the astragalus (= talus) is exclusively with the navicular, and the distal articulation of the calcaneus is strictly with the cuboid. Taxeopody is found in Hyracoidea, Proboscidea, species of Phenacodus and Meniscotherium, and with significant variations in some other extinct ungulate groups (1,5).Most ungulate taxa, including Perissodactyla, share a diplarthral, or alternating, arrangement of the carpals and tarsals, in which podial bones from the proximal and distal rows interlock in a zig-zag fashion (1, 3, 4). Thus, the lunar shares distal articulation with both the ...