The extensor assembly of the finger in lower primates

Abstract

Definition of the order Primates, and sub-groups thereof, is intimately linked to phylogenetic reconstruction. It is also beset by similar problems, notably those of identifying derived similarities and of avoiding circular reasoning. Inclusion of tree-shrews in definitions of living primates and inclusion of Plesiadapiformes in definitions of living and fossil primates are best avoided initially, as both are controversial. For various reasons, it is helpful to define living primates (excluding tree-shrews) first and then to consider as separate issues: (1) the relationships of tree-shrews, and (2) the inclusion of particular fossil groups in the order Primates. Previous definitions of living primates have generally been unsatisfactory and are allied to the belief that, in contrast to many other mammalian orders, primates have no general diagnostic features. It will be shown that living primates excluding tree-shrews can be defined quite clearly on the basis of a shared complex of features involving the dentition, cranial morphology, locomotor adaptations, central nervous organisation and reproductive biology. Certain accessory information relating to habitat preference, geographical distribution and body size effects is also relevant.