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Boyer diss 2009 1046..

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cuboid. The medial side of the bone has distinctive articular facets along the dorsal and<br />

proximal margins (for the mesocuneiform), and along its distal margin (for MT II).<br />

Function.—The presence of an MT II facet indicates that the tarso-metatarsal<br />

joint of MT III was distally positioned relative to that for MT II. Thus the foot would not<br />

have been as mobile as in Cynocephalus and other taxa wherein tarso-metatarsal joints II-<br />

V occur in a single plane perpendicular to the proximodistal axis of the foot. The lack of<br />

ectocuneiforms of other plesidapids and the similarity of the UM 87990 ectocuneiform to<br />

that known for other plesidapiforms obviates the utility of addtional comparative<br />

statements at this time.<br />

Mesocuneiform<br />

Description.—The right mesocuneiform is preserved (Figs. 4.36C, 4.37). It is<br />

slightly smaller than the ectocuneiform and triangular in dorsal view. In lateral view it is<br />

trapezoidal, with smaller dorsoplantar dimensions proximally (4.0 mm) than distally (5.0<br />

mm). The proximal articular surface faces laterally, toward the ectocuneiform, relative to<br />

the proximodistal axis of the bone, while the distal end faces distally. As with the<br />

ectocuneiform, the mesocuneiform is wedge-shaped with a mediolaterally broader dorsal<br />

surface than plantar surface. The lateral surface for articulation with the ectocuneiform is<br />

flat, while the medial surface for articulation with the entocuneiform is concave. The<br />

bone is quite short proximodistally: the length of its lateral side is only 2.8 mm. Thus,<br />

when articulated with the ectocuneiform, its distal metatarsal facet was inset proximally<br />

compared to that of the ectocuneiform (and also compared to the entocuneiform – as<br />

based on entocuneiforms known for other plesiadapids – see Szalay and Dagosto, 1988).<br />

352

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