LOCOMOTOR ADAPTATIONS REFLECTED IN THE WRIST JOINTS OF EARLY TERTIARYPRIMATES (ADAPIFORMES)

The positional behaviors inferred for early Tertiary adapi-form primat es have been the subject of considerable debate. Adapiform wrist morph ology is analyzed here within the context of extant morphoclines in ca rpal joint shape in order to reconstruct adapiform positional behavior . Extant vertical clingers, slow climbers, and arboreal quadrupeds dif fer significantly from one another in length of the m. flexor carpi ul naris lever arm, shape of the midcarpal joint articular surface, and s ize and divergence of the pollical carpometacarpal articulation. These morphological differences are functionally related to differential re quirements for wrist flexion, midcarpal mobility and stability, and po llical grasping, respectively. Adapis, Notharctus, and Smilodectes sha re with living arboreal quadrupeds a tall pisiform body, a mediolatera lly flat midcarpal joint surface, and a relatively unexpanded thumb jo int. Functionally, these features are related to flexing the wrist fro m extended positions during palmigrade, quadrupedal locomotion, increa sing midcarpal joint stability during quadrupedal, weight-bearing post ures, and grasping arboreal supports of predominantly horizontal and o blique orientation. The Messel adapiform (genus indet.) shares certain features of the midcarpal and pollical carpometacarpal articulations with extant vertical clingers, suggesting that this taxon used vertica l substrates more frequently than Other adapiforms. (C) 1996 Wiley-Lis s, Inc.