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unpublished primate dataset reveal some interesting differences. Length-based estimates
are consistently larger than diameter-based estimates using Gingerich’s data. The reverse
is true using the primate-only sample. Compared to other plesiadapids, P. cookei is
estimated to be about the same size as P. tricuspidens, but much larger than other
plesiadapids. Cranial-based estimates of size differences between P. cookei and other
plesiadapids (Chapter 2) can be compared to those from the postcranium by assuming an
isometric relationship between skull size and body mass or by using a regression based
on an extant sample. Both methods are used here. Silcox et al. (in press) present body
mass regressions based on extant primates, which I use here with plesiadapid cranial
length estimates from chapter 2 (see Table 4.38C).
Generally speaking, the skull-based comparisons suggest that the differences
between P. cookei and other smaller plesiadapids were greater than the differences based
on the postcranium-based comparisons (Table 4.38C). However, the skull and
postcranial lengths of P. cookei and P. tricuspidens are consistent in suggesting that these
taxa were the same size. On the other hand, postcranial diameters suggest a substantially
larger body mass for P. tricuspidens.
Digit proportions in P. cookei and other plesiadapids
Kirk et al. (2008) commented on the functional implications of intrinsic hand
proportions in plesiadapiforms. Specifically, they looked at the phalangeal index, the
ratio of the sum of the lengths of the intermediate and proximal phalanges to the length of
the metacarpal of the third digit ray. They found plesiadapids to be diverse in their hand
proportions. N. intermedius and N. gidleyi have fingers that are ~130% the length of the
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