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 : 32-37

Paralouatta MNHNCu 76.1036

Although abrasion has affected most edges of this specimen, reducing the accuracy of measurements, it is clear that the os coxae was large and robustly built in the Cuban monkey, with wide iliac surfaces and a massive dorsal acetabular wall ( fig. 17; table 9). The pubis is shorn off at its acetabular root, and only a small portion of the ischium is preserved. The iliac portion includes most of the sacral articular surface, but nothing remains of its rostral margin. The broad iliac blade is reflected laterally in such a way that the dorsal surface is noticeably concave, as in large Ateles belzebuth or Lagothrix lagotricha . The ischium is broad and appears to have supported a wide and perhaps slightly laterally flaring tuberosity. Nothing, however, in the anatomy of the part preserved suggests that the tuberosity was built out into a platform, as in Old World monkeys. The acetabulum is conspicuously large and slightly more downward-facing than in living large-bodied platyrrhines.

The longest dimension, as preserved, is 115 mm. However, the proportions of the os coxae suggest that it might have exceeded 140 mm in maximum length when intact, which is within the range of coxal lengths found in the largest living platyrrhines.

Functional Considerations

ACETABULAR WALLS: Since the acetabulum and its walls are the only well preserved parts of this specimen, functional remarks will concentrate on this area. Fleagle and Simons (1979) showed that, with some prominent exceptions, nonhuman anthropoids with subequal dorsal and ventral acetabular walls tended to utilize limb suspension in locomotion (and exhibit typically high values for ratio B, cf. table 9). Those with relatively thicker dorsal acetabular walls tended to be more pronograde (with lower values), possibly because in these taxa this part of the os coxae is expanded as an adaptation for weight bearing.

The ratio for Xenothrix AMNHM 259904 calculated by MacPhee and Fleagle (1991) is 0.61, indicating that the Jamaican monkey falls at the low end of the anthropoid spectrum. (Unfortunately, the sciatic margin of AMNHM 268009 is too broken for accurate measurement.) This index was lower than in any platyrrhine specimen measured by Schultz (1969), who recorded the lowest values (0.66–0.68) for this group in female Cebus and Callithrix . However, we found in spot-checking material in the AMNHM collection that Cebus apella expresses indices as low as 0.52, which is similar to the lowest values in Schultz’ (1969) data for cercopithecoids. Conversely, we also found that the only specimen of Brachyteles arachnoides available for study also yielded a relatively low index (0.67), whereas Ateles belzebuth and Alouatta seniculus yielded much higher values (0.95 and 1.04, respectively). The difference among these taxa is due not so much to variability in the thickness of the dorsal wall as to the remarkable gracility of the sparlike ventral wall in the measured specimen of Brachyteles .

Remarkably, ratio B may be even lower in Paralouatta than in Xenothrix . The dorsal acetabular wall measurement for MNHNCu 76.1036 had to be taken at a relatively craniad position, rostral to the damaged area on the sciatic margin ( fig. 17). However, in many primates this part of the dorsal wall is actually narrower than at the figurative equator of the acetabular cup. Abrasion of the cup’s margins also affects measurement, and for this reason the ratio’s value (0.48) in table 9 should be treated with caution. Nevertheless, even after allowances are duly made, we conclude that ratio B is low in this specimen of Paralouatta , perhaps as low as the lowest scores Schultz (1969) recorded in his study for male members, species unspecified, of Macaca (58.4), Papio (55.0), and Cercocebus (52.8) (cf. equivalently low scores for E. patas , L. albigena , and M. nemestrina in table 9). It is noteworthy that, in Schultz’ (1969) study,

(B), medial (C), and lateral (D) aspects (partly after MacPhee and Fleagle, 1991: fig. 4A,C).

females were consistently found to have higher indices than males within the same taxon, indicating that this ratio is affected by sexual dimorphism ( Fleagle and Simons, 1979).

All of the cercopithecid genera just mentioned include species that spend an appreciable portion of their time on low substrates within the canopy, as well as on the ground. However, this ratio is not decisive for separating ground-preferring primates from all others. Although Gorilla and Pan exhibit ratios in the mid-60s, as already noted so does the one specimen of Brachyteles arachnoides available for this study (table 9). Furthermore, decidedly terrestrial T. gelada , not included in Schultz’ (1969) study, has a comparatively high index of 0.62.

According to Fleagle and Simons (1979), ratio C (table 9) is less satisfactory than ratio B for separating quadrupedalists from other locomotor types. Nevertheless, even given the suspect quality of available measurements for Xenothrix and Paralouatta , they clearly group at the low end of the spectrum. Unfortunately, other ratios of interest such as lower ilium length/ischium length could not be computed for Paralouatta because of specimen incompleteness.

FEMUR