Paralouatta

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 : 38-40

Paralouatta MNHNCu 76.1018 and 76.1019

Proximal femur MNHNCu 76.1018 is badly battered ( fig. 20; table 10). Fresh breaks on the specimen’s shaft indicate that the bone was probably broken during the course of recovery, although no diaphyseal fragments in the collection can be precisely fitted to the specimen. The head and greater trochanter are missing, evidently because they were still in the epiphyseal stage at the time of death. The lesser trochanter is present but damaged. The shaft quickly tapers distal to the position of the trochanters, as in platyrrhines generally, but too little is left to allow a good estimate of robusticity or midshaft circumference. The femoral head of Paralouatta was obviously large and spherical, judging from the dimensions of the acetabular cup in MNHNCu 76.1036 (table 9, ratio A). Although the neck of MNHNCu 76.1018 is partially preserved, its angulation in relation to the shaft cannot be reliably established.

The distal epiphysis MNHNCu 76.1019 ( fig. 21), also from an immature animal, pairs well with the proximal femur in terms of relative size, but nothing associates these specimens beyond the fact that they were found in the same chimney fill. As in Xenothrix (and many other mammals) there is a small facet on the posterior articular surface of the lateral condyle for a sesamoid, the lateral fabella. The anterior patellar surface, which is deeper than in Xenothrix , has lost some material just where the craniad border of the epiphysis would have met the diaphysis; however, the measurement (12.3 mm) of this feature is unlikely to be greatly in error.

The lateral condyle is damaged in MNHNCu 76.1019, and therefore condylar width as defined by MacPhee and Fleagle (1991) cannot be taken directly on this specimen. However, one’s visual impression is that the lateral condyle was relatively larger than in Xenothrix , and that therefore the condylar proportionality ratio was actually higher than in the Jamaican monkey (see MacPhee and Fleagle, 1991, for additional comparative data and discussion of ratios).

Functional Considerations

HUMERUS/FEMUR PROPORTIONALITY: The nearly complete humerus AMNHM 268008 and femur AMNHM 259900 of Xenothrix mcgregori are from different localities and therefore represent different adults. Nevertheless, assuming that MacPhee and Fleagle’s (1991) estimate of the length of the Long Mile femur (, 99 mm) is reasonably accurate, and additionally assuming that these two specimens are representative, then femur length in Xenothrix was probably only slightly greater (+5%) than humerus length, i.e. the bones were subequal. In New World suspensory taxa, the humerus tends to be slightly longer ( Brachyteles arachnoides , Ateles belzebuth ) than the femur or the bones are subequal ( Lagothrix lagotricha ). In Alouatta seniculus the femur is slightly longer. If humerus/femur proportionality were similar to that inferred for Xenothrix , then extrapolation from the length of the nearly complete humerus MNHNCu 76.1010 would produce an estimat- ed femur length of, 150 mm for Paralouatta , which is similar to Alouatta seniculus .

DISTAL EPIPHYSIS ANTEROPOSTERIOR COM- PRESSION AND CONDYLAR PROPORTIONALITY: As noted, the architecture of the femoral distal epiphysis is similar in Xenothrix and Paralouatta in that the distal epiphysis is anteroposteriorly compressed and the condyles are asymmetrical. These are common features of arboreal quadrupeds and climbers. However, in the Antillean monkeys the degree of compression is not as extreme as it is in the suspensory atelines and pitheciines. Arboreal quadrupeds, and to a greater degree terrestrial quadrupeds, have rather tall femoral condyles and narrow patellar grooves ( MacPhee and Fleagle, 1991; Meldrum, 1993). The intact portions of the condyles of Paralouatta are noticeably taller than those of Xenothrix , and the patellar groove has greater relief and depth. However, it is not obvious how to interpret the significance of patellar groove breadth, as it is wider in pitheciines (chiefly climbing locomotion) than it is in atelines (chiefly suspensory locomotion) ( Lockwood, 1999). In overall proportions of the distal femur, xenotrichins resemble Miocene platyrrhines such as Carlocebus and Homunculus ( Meldrum and Kay, 1997) .

TIBIA