The frugivorous insectivores? Functional morphological analysis of molar topography for inferring diet in extant treeshrews (Scandentia)

The ecology, and particularly the diet, of treeshrews (order Scandentia) is poorly understood compared to that of their close relatives, the primates. This stems partially from treeshrews having fast food transit times through the gut, meaning fecal and stomach samples only represent a small portion of the foodstuffs consumed in a given day. Moreover, treeshrews are difficult to observe in the wild, leading to a lack of observational data in the literature. Although treeshrews are mixed feeders, consuming both insects and fruit, it is currently unknown how the relative importance of these food types varies across Scandentia. Previous study of functional dental morphology has provided an alternative means for understanding the diet of living euarchontans. We used dental topographic metrics to quantify aspects of functional dental morphology in a large sample of treeshrews (n = 58). We measured relief index, Dirichlet normal energy, and three-dimensional orientation patch count rotated, which quantify crown relief, occlusal curvature, and complexity, respectively. Our results suggest that treeshrews exhibit dental morphology consistent with high levels of insectivory relative to other euarchontans. They also suggest that taxa such as Dendrogale melanura and Tupaia belangeri appear to be best suited to insectivory, whereas taxa such as T. palawanensis and T. gracilis appear to be best adapted to frugivory. Our results suggest that Ptilocercus lowii is characterized by a dentition better adapted to insectivory than the early primate Purgatorius. If P. lowii represents a good modern analogue for primitive euarchontans, this contrast would support models of primate origins that include a shift to greater frugivory.

Ecometric modelling of tooth shape and precipitation gradients among lemurs on Madagascar

Ecometric modelling relates spatial environmental variables to phenotypic characters to better understand morphological adaptation and help reconstruct past environments. Here, the community means of the dental topography metrics Dirichlet normal energy (DNE) and orientation patch count (OPC) are tested against annual precipitation and precipitation seasonality among lemurs across Madagascar. Dry, seasonal environments are expected to be associated with high DNE and OPC, as lemurs living in these environments are more likely to rely on tougher foods. Ecometric models are also used to calculate ecometric loads for lemur taxa hypothesized to be experiencing evolutionary disequilibria and to reconstruct annual precipitation and precipitation seasonality at the ~500 years BP subfossil cave site of Ankilitelo. DNE was highest in highly seasonal but wet environments. Seasonal exploitation of fallback foods and the availability of new leaves during wet periods may be most important in driving community DNE. OPC was weakly predicted by annual precipitation and seasonality but its distribution appeared to be driven by a stepwise increase in its community values in rainforest environments. The lemur fauna from Ankilitelo appears to resemble communities from moister environments than occur in the spiny desert zone in which the site is situated today.