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Boyer diss 2009 1046..

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Plesiadapis tricuspidens MNHN BR 17414-19, 1371<br />

These specimens represent isolated petrosals from Berru identified by M.<br />

Godinot. In all cases I assessed the morphology independently and confirmed the<br />

attribution to P. tricuspidens. The specimens have been measured from HRxCT scans<br />

generated at Pennsylvania State University at a resolution of 0.0500 mm for pixel<br />

dimensions, and 0.0581 mm for slice spacing. MNHN BR 17418 preserves a stapes that<br />

has fallen into the cochlea. This element was digitally extracted, measured, and helps<br />

confirm that P. tricuspidens did not have a functional stapedial artery. The area of its<br />

obturator foramen is small relative to its footplate length, which makes it like modern<br />

primates that lack stapedial arteries (Coleman and <strong>Boyer</strong>, 2008; in prep.).<br />

Table 2.3 is a codified description of these specimens and other petrosal<br />

specimens studied here. The presence/absence and measurements of various features is<br />

documented therein. None of these specimens reveals an apparent suture at the boundary<br />

between the medial tympanic process and the promontorium as in the case of the Pellouin<br />

skull.<br />

SELECT QUANTITATIVE DIFFERENCES BETWEEN P. TRICUSPIDENS AND<br />

OTHER PLESIADAPIDS<br />

As mentioned in the introduction, features thought to be distinctive for<br />

plesiadapids, as based on observations of P. tricuspidens, prior to this work, include a<br />

nasal bone that is narrow at its caudal extent; a premaxilla that has a broad contact with<br />

the frontal; and a tubular-shaped ectotympanic (e.g., Bloch et al., 2007). Table 2.5<br />

70

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