The suggestion that the earliest primates were large (>1 kg) contrasts with the current consensus view that the first primates were small with body weights in the range of mouse and dwarf lemurs (e.g., Cartmill, 1974a; Dagosto, 1988; Martin 1972, 1990). Some other evidence, however, has also pointed to the possibility that the first primates were larger than previously thought (Soligo, 2001; Soligo and Müller 1999a,b). The presence of nails as opposed to functional claws on the digits of the foot and hand is thought to be a defining characteristic of the order Primates (see Soligo and Müller, 1999b). Despite this, the issue of why functional claws should have been lost in the lineage that led to the last common ancestor of modern primates is still contentious (e.g., Cartmill, 1974a, 1985, 1992). It has recently been argued that functional claws were reduced to nails as a result of a phyletic increase in body mass in the lineage leading to the last common ancestor of modern primates (Soligo, 2001; Soligo and Müller, 1999a,b). A recent comparison of the size distribution of claw-bearing and nail-bearing species of arboreal mammals has added support to this hypothesis, as it revealed that the nail-bearing species were significantly larger than the claw-bearing species (Soligo, 2001). Based on the details of the size distributions of the two groups, Soligo (2001) argued that a weight of more than 800 g was attained in the lineage that led to the last common ancestor of modern primates. That estimate is in agreement with the findings of Müller and Soligo (2005) discussed earlier.
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