Notharctus

Abstract: The length proportions of the primate hands and their elements are analyzed in 43 extant genera and 6 fossil genera. The length of the hand in relation to the forelimb length does not characterize taxonomic groups, but rather locomotor modes, such as vertical-clinging-and-leaping, claw-climbing, and terrestrial quadrupe-dalism, as opposed to arboreal quadrupedalism. The relative lengths of the carpus, metacarpus, and digits appear mainly related to the phylogenetic history of the primates. Paraxony, instead of mesaxony, is the most frequent pattern of the simiiform hand, whereas hypermesaxony characterizes humans, hylobatids, and tarsiers. The proportions of the primitive euprimate hand are discussed in the light of the hand proportions of extant primates. Proportions drawn from hand remains of Megaladapis edwardsi, Proconsul africanus, Mesopithecus pentelici, Notharctus, Adapts parisiensis, and Plesiadapis insignis are compared to those of extant primates, and discussed from both phylogenetical and functional points of view.

Abstract: I. On the Relationship of the Eocene Lemur Notharctus to the AdapidAE and to other Primates 2 RESULTS OBTAINED BY OTHER INVESTIGATORS The genus Notharctus was founded by Leidy in 1870 upon a small fossil jaw which had been found in the Eocene formation near Fort Bridger, Wyoming. Leidy was not able to refer the animal to any existing order of mammals. He noted its resemblances to carnivorous mammals on the one hand and to certain supposed Eocene pachyderms on the other. Marsh, who described a similar jaw fragment the next year, 1871, also noted its resemblances to the supposed suilline pachyderm Hyopsodus. In October, 1872, however, Marsh described some better specimens, which included parts of the limb bones. He remarked that the principal parts of the skeleton of these animals were formed much as in some of the Lemurs, especially the limb bones, and he referred the animals to . . .

Abstract: A recently discovered partial skeleton of the adapid Cantius trigonodus from the early Eocene Willwood Formation of the Bighorn Basin, Wyoming, documents substantial new information about the anatomy of the oldest lemuriform primates. It is very similar in all features to its descendant, middle Eocene Notharctus, and both exhibit numerous resemblances to certain extant Malagasy lemurs, particularly Lepilemur, Propithecus, Lemur, and Hapalemur griseus. Like these forms, Cantius had relatively long hind limbs and short forelimbs. Forelimb traits (prominent brachialis flange of the humerus, well-developed olecranon process of the ulna, and strong shafts of the ulna and radius) suggest active use of the forelimbs in progression. Specializations in the hind limb (e.g., expanded articular surface of the femoral head, narrow and elevated patellar trochlea and prominent lateral trochlear ridge, posteriorly oriented femoral and tibial condyles, narrow and elongate talus, and hallucal metatarsal with prominent peroneal tubercle) indicate capabilities for leaping and for powerful grasping with an opposable hallux. Cantius was presumably primitive in having a relatively long ischium and much more distal inferior tibial tuberosity than most extant lemurs—traits suggesting that powerful extension of the thigh and flexion at the knee were important in its locomotion and posture. We interpret Cantius as an active arboreal quadruped with a propensity for leaping. The existence of this skeletal structure in one of the oldest primates of modern aspect suggests that it represents the primitive lemuriform morphology.

Abstract: We describe the morphology of the first complete incisor-canine complex for Notharctus tenebrosus. Gregory’s classic description, based on heavily reconstructed and fragmentary mate