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Boyer diss 2009 1046..

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flexor fibularis groove surface. Expansion of the flexor fibularis groove surface could<br />

conceivably have been the progressive result of high stresses on this surface caused by<br />

the flexor fibularis tendons that run under it. Second, and less likely as a result of<br />

pathology, the astragalar neck is proportionally longer compared to the astragalar body in<br />

P. cookei as compared to other plesiadapids.<br />

Calcaneum<br />

Description.—UM 87990 preserves a complete right and fragmentary left<br />

calcaneum (Fig. 4.29B; Table 4.21A-C). Plesiadapid calcanea are relatively well known<br />

(Szalay and Decker, 1974). Most descriptive features applying to these published<br />

specimens also apply to the calcaneum of P. cookei.<br />

The most distinctive feature of the calcaneum of P. cookei is the large peroneal<br />

tuberosity on the lateral side, which covers 40% of the proximodistal length of the bone.<br />

Because of its great length, it arises from the tuber proximal to the distal end of the ectal<br />

facet; however, it does not project distally beyond the calcaneocuboid facet. The<br />

dorsoplantar depth is also relatively large. The lateral surface of the tubercle is marked<br />

by a deep groove that crosses it obliquely from dorsoproximal to plantodistal.<br />

The calcaneal tuber and posterior calcaneoastragalar (ectal) facet represent a bit<br />

less than two-thirds the length of the bone. The tuber is deep dorsoventrally relative to its<br />

proximodistal length. The proximal end is mediolaterally wider than the shaft of the<br />

tuber distal to it. The medial side of the tuber projects more strongly medially than the<br />

lateral side projects laterally. The ectal facet is shaped like a segment of a cone with its<br />

tip truncated. The axis of ectal facet points almost medially relative to the proximodistal<br />

345

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