Semi-supervised determination of pseudocryptic morphotypes using observer-free characterizations of anatomical alignment and shape.

Accurate, quantitative characterization of complex shapes is recognized as a key methodological challenge in biology. Recent development of automated three-dimensional geometric morphometric protocols (auto3dgm) provides a promising set of tools to help address this challenge. While auto3dgm has been shown to be useful in characterizing variation across clades of morphologically very distinct mammals, it has not been adequately tested in more problematic cases where pseudolandmark placement error potentially confounds interpretation of true shape variation. Here, we tested the sensitivity of auto3dgm to the degree of variation and various parameterization settings using a simulation and three microCT datasets that characterize mammal tooth crown morphology as biological examples. The microCT datasets vary in degree of apparent morphological differentiation, with two that include grossly similar morphospecies and one that includes two laboratory strains of a single species. Resulting alignments are highly sensitive to the number of pseudolandmarks used to quantify shapes. The degree to which the surfaces were downsampled and the apparent degree of morphological differentiation across the dataset also influenced alignment repeatability. We show that previous critiques of auto3dgm were based on poorly parameterized alignments and suggest that sample-specific sensitivity analyses should be added to any research protocol including auto3dgm. Auto3dgm is a useful tool for studying samples when pseudolandmark placement error is small relative to the true differences between specimens. This method therefore represents a promising avenue forward in morphometric studies at a wide range of scales, from samples that differ by a single genetic locus to samples that represent multiple phylogenetically diverse clades.

Myrmecophagous microwear: implications for diet in the hominin fossil record.

An increasing body of data supports the concept that early humans ate invertebrate prey items, especially insects, and that insects may have been a substantial protein source. Insects are ubiquitous throughout the landscape and of high nutritional value. Given that all modern apes and many human groups eat insects, it is likely that early hominins did as well. However, it is unknown how much, which type(s), and what foraging strategy was utilized to obtain invertebrate prey. Given that gross masticatory anatomy of early hominins, like modern apes, fails to reflect their insectivorous proclivities, dental microwear analysis might be a useful tool for identifying this behavior in our fossil ancestors. Dental microwear data was collected on three primarily myrmecophagous mammals and compared to the literature on other faunivorous, frugivorous, and folivorous species. Results indicate that myrmecophagous species have comparable pit frequencies with other faunivores and pit frequency generally distinguishes them from folivores but not all frugivores. Additionally, myrmecophagous mammals have unusually high feature densities, like other faunivores, and density is the microwear signal most suggestive of some sort of faunivory.

Lemur habitat and dental senescence in Ranomafana National Park, Madagascar.

Not only can teeth provide clues about diet, but they also can be indicators of habitat quality. Conspecific groups living in different habitats with different kinds of foods may exhibit different rates of dental attrition because their teeth are less well adapted to some foods than to others. Ecological disequilibrium describes the situation in which animals live in habitats to which they are relatively poorly adapted. We test whether dental senescence, the wear-related decrease in dental functionality that is associated with decreased survival of infants born to older Propithecus edwardsi females, can be explained by ecological disequilibrium. Specifically, we compare the rates of dental wear in sifaka groups living in nearby habitats that differ in the degree of anthropogenically induced disturbance. We hypothesize that sifakas living in disturbed areas have an unusual rate of tooth wear compared to those living in a more pristine area, and that dental senescence is a consequence of an atypically high wear rate in a degraded habitat. To test whether habitat quality affects tooth wear more generally, we compare rates of use-wear in two subsets of Microcebus rufus living in either relatively undisturbed or disturbed habitats. Contrary to our predictions, we did not detect different rates of tooth wear in disturbed versus undisturbed habitats for either species and consider that reproductively detrimental dental senescence in P. edwardsi females is unlikely to be a pathological consequence of ecological disequilibrium.