Boyer diss 2009 1046..

Manubrium and Sternebrae
Description.—The manubrium and six sternebrae are preserved (Fig. 4.48; Table
4.31). None of these elements are known for any other plesiadapiforms. The manubrium
is longer than any of the sternebrae (Table 4.31). The right costal process is broken but
the left one is intact. Its lateral edge received the first rib. On its craniodorsal aspect a
slight depression for the clavicle articulation is observable. The cranial margin of the
manubrium is convex. The dorsal surface is flat. The ventral surface is marked by a
strong midline keel. The keel is narrowest at its root. Thus, a transverse cross-section
through the manubrium reveals it to be in the shape of an “I-beam.”
The articular surface for the first sternebra is oriented somewhat ventrally. Thus,
when articulated, the manubrium and first sternebra form an obtuse ventral angle. The
sternebrae are blocky bones and are all fairly similar to each other. The first is strongly
keeled, while the keel becomes increasingly muted on more caudal positions. The last
sternebra differs from the others in having a caudal end that is rounded instead of flat,
and in having a longitudinal groove on its dorsal surface.
Comparison.—The manubrium of P. cookei appears more similar to that of
Tupaia glis than to those of many euprimates in having a stronger keel and in forming a
strong angle with the first sternebra.
Ribs
Description.—Twelve rib fragments are attributed to UM 87990 (Fig. 4.49; Table
4.32). Six appear to be left side elements. One or two of the floating ribs (T10-13) are
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