Boyer diss 2009 1046..

Caudal vertebrae
Description.—There are 17 caudal (Ca) vertebrae attributed to UM 87990 (Fig.
4.45; Table 4.30). The most proximal position preserved (Fig. 4.45A) has a complete
vertebral canal, pre- and postzygapophyses, posteriorly projecting transverse processes,
and the broken base of a spinous process. The centrum is missing but it would have been
relatively craniocaudally short and mediolaterally wide. Typically there are three
proximal caudal vertebrae with these basic proportions, as there are in the most
completely known plesiadapiform tail of Ignacius clarkforkensis (Boyer and Bloch,
2008). The next most proximal caudal vertebra still retains a complete vertebral canal,
but it is substantially more elongate than the first (but shorter and less elongate than the
next in the series). This appears to be either Ca4 or Ca5 (Fig. 4.45B). The following
vertebra appears to be Ca6 (Fig. 4.45C). It is much longer than the first two. It has an
incomplete vertebral canal (the laminae do not meet in the sagittal plane). The pre- and
post zygapophyses did not directly articulate with those of more proximal and distal
vertebrae, respectively. There is a set of cranioventrally projecting transverse processes
and a set of caudoventrally projecting processes. The vertebra identified as Ca7 is very
similar to Ca6. It differs in being absolutely longer, proportionally narrower, and in
having absolutely and proportionally smaller transverse processes. From Ca8-Ca12 (Fig.
4.45E-I) the vertebrae are identified on the basis of increasing length and/or decreasing
prominence of zygapophyses and transverse processes. The centrum diameters of these
vertebrae do not appear to vary drastically or systematically through this region. Ca11
and Ca12 (Fig. 4.45H, I) are extremely similar to one another and it is possible that their
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