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etween the distal carpals and the “set 1” metacarpals than between the distal carpals and
the “set 2” metacarpals (Table 4.12).
Metacarpus function.—The wedge-shaped proximal ends of MC II-IV articulate
to produce a pronounced transverse metacarpal arch (Fig. 4.15B). Napier (1961)
explained that this gives the hands the capacity for convergence (i.e., when the proximal
interphalangeal joints flex, the finger tips converge on each other), which enhances
grasping ability. The extensive dorsally-facing part of the distal articular surfaces
indicates the capacity for stabile “hyper-dorsiflexed” finger postures as are used in
pronograde and orthograde quadrupedal locomotion (Jenkins, 1974).
Proximal phalanges
Proximal phalanx of first digit description.—Three elements referable to this
bone are preserved. These include proximal bases of what appear to be both hallucal
proximal phalanges (Fig. 4.19), and a third fragmentary base and shaft of the left pollical
proximal phalanx. The elements are too fragmentary for meaningful quantification of
their morphology, although a few measurements are given in Table 4.13. The bones are
recognizable as such by comparison to previously identified first digit proximal
phalanges of P. tricuspidens and N. intermedius (Beard, 1989). Hallucal and pollical
elements are distinguished here for the first time based on the much larger size of the
hallucal elements. The proximal end of this bone is distinct among the proximal phalanx
sample in the asymmetry of tubercles that laterally flank and extend ventral to the
proximal articular surface. The medial side tubercle is blunt and proximally restricted,
while the lateral side tubercle is pointed and proximally extended beyond its partner (Fig.
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