The primates (see Chapter 11) seem to have affinities with tree shrews and flying lemurs (Novacek et al., 1988), based on that fact that these animals are graced with a 'pendulous penis suspended by a reduced sheath between the genital pouch and the abdomen'! In addition, archontans all share some specializations of the ear region of the skull (Beard, 1993). Initially, molecular data were unclear about the reality of the clade Archon-ta,but it is confirmed by current analyses (see Box 10.6).
Within Archonta, Beard (1993) proposed a clade Primatomorpha, which consists of primates and flying lemurs, based on shared characters of the dentition and digestive systems that relate to fruit-eating. On the other hand, the molecular trees suggest that primates are the outgroup to a clade consisting of tree shrews and flying lemurs. Archonta and Glires (rodents + rabbits) together make up the larger clade Euarchontoglires.
10.12.1 Plesiadapiforms: basal archontans
The Plesiadapiformes are a group of six or seven families that radiated in the Palaeocene and Eocene of North America and western Europe. Their oldest representative is Purgatorius, known from teeth and jaw fragments from the early Palaeocene (Buckley, 1997). A supposed Late Cretaceous record, once billed as the first true primate, is discounted now. The best known plesiadapi-form is Plesiadapis itself from the lower Eocene of North America andFrance (Figure 10.41(a)),a squirrellike animal with strong claws on its digits and adaptations for tree-climbing (Simons, 1964). The eyes are large, but face sideways, a primitive character. The long snout bears large rodent-like incisors, with large gaps behind and broad cheek teeth for grinding plant food.
Plesiadapiforms were formerly often treated as basal primates because of dental similarities to the Adapidea, which are uncontested primates (see p. 366), whereas Beard (1993) argued that they share synapomorphies of the skull and limbs with the flying lemurs. New material of the plesiadapiform Carpolestes leads Bloch and Boyer (2002) to reconfirm affinities with true primates based on characters of the brain region.
10.12.2 Scandentia: tree shrews
The 19 or so extant species of tree shrews of south-east Asia look rather like small squirrels with pointy noses, and yet their relationships have generally been sought either with the insectivores or the primates. The skull (Figure 10.41(b)) is primitive in many respects,but superficially primate-like in the enlarged brain and large eyes. Fossil tree shrews include possible examples from the Eocene of China and unequivocal material from the Miocene ofIndia.
10.12.3 Dermoptera: flying lemurs
The flying lemurs are represented today by one genus, the colugo Cynocephalus of south-east Asia (Figure 10.41(c)), which has a gliding membrane between its limbs, body and tail, a broad flap of skin that allows it to leap for up to 100 m between trees. It has a reduced ulna and fibula, broad cheek teeth and comb-like middle incisors. It feeds on leaves and fruit. Until recently, flying lemurs had no fossil record, but an Eocene example has been reported from Thailand. Some fossil groups, such as the palgiomenids and paromomyids of the Palaeocene and early Eocene of North America, may be relatives ofDermoptera.
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