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 : 40-43

Paralouatta MNHNCu 76.1034

MNHNCu 76.1034 is the distal end of a right tibia, with half (or less) of the shaft preserved ( fig. 23; table 11). The posterior and lateral aspects of the distal end are damaged, including the area where the fibular notch was situated. The interosseous border is faintly indicated, but otherwise there are no strong lines or muscle markings on the shaft. The anterior ‘‘border’’ is smoothly rounded rather than sharp, as in platyrrhines generally. The diaphysis was probably relatively straight, as it is in most but not all platyrrhines ( fig. 25B, F, J), although with only half of the element available this point cannot be settled.

The medial aspect of the distal tibia of Paralouatta is distinctive: the shaft is quite massive anteroposteriorly, and terminates distally in a wide, blunt malleolus ( fig. 23B). The anterolateral aspect of the malleolus terminates in a poorly defined facet ( fig. 23A) for the cotylar fossa of the talus. In primates generally the malleolus tends to be pyramidal rather than rectangular ( fig. 25), but the specimens of Ateles belzebuth ( fig. 25F) and Lagothrix lagotricha ( fig. 25J) in the comparative set show some approximation to the condition in Paralouatta .

Note also that, in posterior view ( fig. 23C), the tibia’s lateral surface is remarkably straight compared to tibiae of other largebodied platyrrhines such as Ateles and Lagothrix ( fig. 25G, K), in which the lateral surface of the distal end is slightly projecting. The squared-off appearance of the region of the fibular facet resembles the condition in many catarrhines ( Hershkovitz, 1988; cf. Lophocebus , fig. 25O). This arrangement may have allowed the distal moiety of the fibular shaft to be closely approximated to the facing surface of the tibia (cf. Meldrum and Kay, 1997). However, it is also clear that, unlike Lophocebus , the lateral margin of the distal articular surface is not deeply notched by the fibular facet in Paralouatta ( fig. 23D). The significance of this is uncertain, because according to Ford (1986a) Old and New World monkeys differ markedly in the size and depth of the fibular facet.

Finally, the malleolus bears a small excavation ( fig. 23C) where one might expect a groove for the tendon of tibialis posterior m. (as in Cebus , fig. 25C). However, the floor of the groove is rough rather than smooth, and the feature itself is oriented at an angle impossible for the tendon to assume. Bone lateral to this area is badly abraded and it is not clear whether there were grooves for this last muscle or flexor digitorum longus m.; on the whole it seems doubtful that there were.