ABSTRACT
Here we describe new fossil material of Antillothrix bernensis, a Pleistocene-Holocene primate taxon from Hispaniola. It is now represented by seven crania, five mandibles, and dozens of postcranial elements from several paleontologically rich cave systems. The five adult crania included here share a similar overall profile as well as specific features such as a deep depression at the glabella. The complete anterior dentition of Antillothrix can now be described for the first time; short canine crowns, in the apicobasal dimension, compare well with titi monkeys, but the new crania and mandibles lack the specialized tall-crowned incisors of the extant pitheciids. They do, however, have a diastema between the lateral maxillary incisors and canines, a feature not present in the previously known crania. The new mandibles deepen posteriorly and have a medial inflection of the mandibular ramus, as in some pitheciids, but also share with Xenothrix a significant vertical narrowing of the corpus under P4/M1 not observed among extant taxa. Two of the specimens, a cranium and a mandible that do not fit together, exhibit congenitally absent third molars-a rarity among extant, noncallitrichine taxa. There is an approximately 1-kg range in the estimated body mass among the full Antillothrix sample (from 2.4 to 3.4 kg), as well as a range of approximately 5 cm3 of endocranial volume (from 40 to 45 cm3). With these extended ranges from the new specimens, Antillothrix can no longer be described as a taxon with a brain size smaller than that expected for its body size. Neither of these ranges in the brain size or body size is large enough to indicate a substantial level of sexual dimorphism or to necessitate separating the sample into male and female individuals. Given this, and the similar canine sizes for all specimens where they are present, the sample is consistent with a morphologically variable but monomorphic species.
ABSTRACT
OBJECTIVES: Platyrrhines constitute a diverse clade, with the modern Atelidae exhibiting the most variation in cranial and endocast morphology. The processes responsible for this diversification are not well understood. Here, we present a geometric morphometric study describing variation in cranial and endocranial shape of 14 species of Alouatta, Ateles, Brachyteles, and Lagothrix and two extinct taxa, Cartelles and Caipora. METHODS: We examined cranial and endocranial shape variation among species using images reconstructed from CT scans and geometric morphometric techniques based on three-dimensional landmarks and semilandmarks. Principal components analyses were used to explore variation, including the Procrustes shape coordinates, summing the logarithm of the Centroid Size, the common allometric component, and residual shape components. RESULTS: Differences in endocranial shape are related to a relative increase or decrease in the volume of the neocortex region with respect to brainstem and cerebellum regions. The relative position of the brainstem varies from a posterior position in Alouatta to a more ventral position in Ateles. The shape of both the cranium and endocast of Caipora is within the observed variation of Brachyteles. Cartelles occupies the most differentiated position relative to the extant taxa, especially in regards to its endocranial shape. CONCLUSIONS: The pattern of variation in the extant species in endocranial shape is similar to the variation observed in previous cranial studies, with Alouatta as an outlier. The similarities between Caipora and Brachyteles were unexpected and intriguing given the frugivorous adaptations inferred from the fossil's dentition. Our study shows the importance of considering both extant and fossil species when studying diversification of complex traits.