One of the most controversial issues in primate palaeontology concerns the phylogenetic position of the extinct primate inf raorder Adapiformes 1,2. During the Eocene, this group of primates of modern aspect possessed a holarctic distribution1-12, and may have been present in the poorly known Palaeogene of Africa10. Mainly on the basis of craniodental morphology, at least four hypotheses have been proposed concerning the phylogenetic interrelationships among adapiforms and other primate higher taxa: (1) that adapiforms are ancestral to both lemuriforms (including Lorisoidea) and anthropoids8-10'13; (2) that adapiforms cannot be shown to possess a special phylogenetic relationship with either lemuriforms14'15 or anthropoids15-18; (3) that adapiforms are the sister taxon of lemuriforms16-18; and (4) that Adapiformes is not a natural, monophyletic group, but rather consists of nested clades within the radiation of lemuriforms19-25. Here, we describe features of the ankle and wrist joints of several adapiform taxa that provide an independent test of the preceding hypotheses. These traits suggest that lemuriforms are monophyletic with respect to known adapiforms, but that adapiforms nevertheless are their stem lineage (sensu Ax26).
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