The Jaw Adductor Musculature in Notharctine Primates

Abstract

The dimensions of the jaw adductor muscles provide a complement to dental morphology in reconstructing diets of fossil primates. A dataset of jaw adductor dimensions and related osteological measurements in extant strepsirrhine primates provided the basis for jaw muscle reconstruction in European Eocene adapoids and Malagasy subfossil lemurs. Here, the same method is applied to North American Eocene adapoids. I used caliper measurements, along with areas and distances from digital 3D scans to estimate muscle size, leverage, and bite force in Smilodectes and Notharctus (Notharctinae). Notharctines plot among extant strepsirrhines for most masticatory variables relative to skull size. In general, their muscle size is modest compared to that of European adapoids and subfossil lemurs. Molar morphology suggests that Smilodectes and Notharctus were adapted to processing tough foods such as leaves. Condyle height in these genera suggests that they were not adapted for wide gapes. Chewing muscle leverage is poorer in Notharctus than in Smilodectes, mainly as a consequence of the longer face in Notharctus. Differences in masticatory robusticity between the largest European Eocene primates and the largest North American Eocene primates suggest a greater availability of large, soft fruits to the latter. A AAA Short-Term Visiting Scholarship generously supported this project.