Xenothrix AMNHM

Phee, R. D. E. M & Meldrum, Jeff, 2006, Postcranial Remains of the Extinct Monkeys of the Greater Antilles, with Evidence for Semiterrestriality in Paralouatta, American Museum Novitates 3516, pp. 1-66 : 30-32

Xenothrix AMNHM 268009

AMNHM 268009, the Skeleton Cave coxal specimen ( fig. 16A–C; table 9), is as incomplete as AMNHM 259904 from Long Mile Cave ( fig. 16D–F) described by MacPhee and Fleagle (1991). The only noteworthy feature that is better preserved in the former is the superior ramus of the pubis. MacPhee and Fleagle (1991) inferred on the basis of the Long Mile specimen that, in the intact state, the superior ramus would have jutted at a wide angle from the coxal body; the new specimen confirms this. By superimposing images of AMNHM 2599004 (more complete ischium) on AMNHM 268009 (more complete pubis), it can be established that in Xenothrix the superior ramus departs the coxal body at somewhat less than a right angle (75–80 °). Old and New World monkeys alike, especially larger species, display broadly similar angles ( MacPhee and Fleagle, 1991; Meldrum, 1993; Meldrum and Kay, 1997).

In the new specimen ( fig. 16A), the superior ramus is notably gracile, flat, and craniocaudally narrow. The maximum distance from the approximate center of the acetabulum to the medial end of the pubis as preserved is 27.3 mm. On the broken medial margin no rugosities or other features are present which might serve to indicate that part of the true symphyseal surface is preserved. Evidently, in the intact state the complete ramus would have been longer still. On the underside of the superior ramus there is another broken surface (arrow, fig. 16A), the site of the inferior ramus of the pubis. Although the shape of the obturator foramen cannot be inferred from the evidence at hand, it must have been relatively large, as the root of the inferior ramus lies at a considerable distance from obturator margin of the acetabular region.

The acetabulum is notably wide in both specimens. Acetabular depth is approximately one-half of acetabular diameter (ratio A, table 9), as is typical for primates ( Schultz, 1969). Owing to the condition of the new specimen, in which the sciatic margin is broken away ( fig. 16C), dorsal and medial acetabular wall dimensions could not be taken. However, the ventral wall is intact and its measurement resembles that of AMNHM 259904 (table 9).

MacPhee and Fleagle (1991) noted previously that the locomotor correlates of the Long Mile os coxae were indeterminate; the Skeleton Cave specimen sheds no new light on

TABLE 8

Radius: Paralouatta varonai, Dimensions (in mm)

a

MNHNCu

Dimensions 76.1015

1. Length (as is) 31.6e 2. Head, APW 10.2e 3. Head, circumference 30.4e 4. Biceps, (radial) tuberosity length 15.0

5. Shaft, minimum APW 5.0

a Measurements in italics are not precise (e 5 estimate, due to damage or breakage).

this question. However, they noted that the expanded iliac planum is consistent with slothlike slow quadrupedalism or climbing, as is the gracile and apparently elongated pubic ramus.