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vertically-to-caudally projecting third spinous process; and (20) the tail of P. cookei was
relatively long with the longest vertebrae of the tail occurring at the 11 th or 12 th position.
Estimation of body mass based on the postcranium and using different sets of
regressions reveals plesiadapids to have ranged from between around 300 g (Nannodectes
intermedius) to 2000-3000 g (both P. cookei and P. tricuspidens) in mass. This is
basically consistent with, although slightly lower than, estimates of mass range derived
from cranial material.
Consideration of morphology, joint mobility and likely habitual postures strongly
supports previous contentions that P. cookei was committed to an arboreal lifestyle
(Gunnell and Gingerich, 1987; Bloch et al., 2007), although they do not necessarily add
strong support to the idea that it had “suspensory tendencies” (Bloch and Boyer, 2007;
Boyer and Bloch, 2008).
Phylogenetic implications of new observations
Chapter 5 provides the first species level cladistic analysis focused on members of
the Plesiadapidae. The analysis of 30 species generates a cladogram that is consistent
with phylogenetic hypotheses of Gingerich (1976) in most respects. Some polytomies in
this cladogram may only be resolvable by incorporation of stratigraphic evidence. States
for cranial and postcranial morphological characters are optimized onto the ancestral
node of this species level cladogram. The optimized codings for the ancestral node are
then used to revise the codings for a higher level “Plesiadapidae” taxon in recently
published matrices (Bloch and Boyer, 2002, 2007; Bloch and Silcox, 2006). Revision of
these codings for Plesiadapidae reveals that the previous phylogenetic signal in these
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