Boyer diss 2009 1046..

Principal coordinates analysis of the Euclidean distance matrix reveals all
available plesiadapid astragali to be basically similar to each other. The astragali of two
extant euprimates, a dermopteran, a treeshrew, a fossil adapiform, and Deccanolestes (a
fossil, possible euarchontan from India) plot in different parts of the principal coordinates
space (Fig. 4.32), and do not overlap with region occupied by the plesiadapids. It is
interesting to note that astragali of Cynocephalus volans, Loris tardigradus, and the
adapiform are morphologically closer to each other and those of plesidapids than they are
to astragali of the other euprimate (Galago moholi) or Tupaia glis. This is apparent
visually and also by taking into consideration the minimum spanning tree between data
points. Considered feature by feature, the morphospace proximity makes some sense
(e.g., L. tardigradus, C. volans, and the adapiform have a laterally curved medial tibial
facet and an elliptical, rather than circular shape to its astragalar head, like those of
plesiadapids but unlike those of G. moholi or T. glis), and it may further support the
interpretation of plesiadapiforms by Beard (1989) as being slow, cautious arborealists.
The astragalus of P. cookei differs from those of other plesiadapids in at least two
notable ways. First, it has a more proximodistally expanded proximal end to its medial
tibial facet. In fact this expansion almost appears pathological because, as a
consequence, the concave part of the sustentacular facet into which the sustentaculum of
the calcaneus must insert for articulation has been narrowed substantially. The concavity
is actually too narrow for the calcaneal element to fit into it easily and flushly contact the
astragalar surface. The increase in the proximodistal depth of the medial tibial articular
surface and consequent narrowing of the concavity of the proximal part of the
sustentacular facet appears to also be correlated with proximoventral expansion of the
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