Document Type
Thesis
Abstract
Microvertebrate assemblages can provide substantial insight into the paleoecology and evolution of Mesozoic reptiles, but taxonomic and ecomorph identifications using qualitative characteristics remains rare. For this project, we quantified morphological differences in a large sample (n > 200) of fossil teeth from a Norian microvertebrate assemblage from the ‘Green Site’ locality (Chinle Formation, Arizona) to devise a replicable set of morphological characters to differentiate teeth. Comparing these data to Middle Triassic reptilian assemblages from similar paleoenvironments allows us to track trends in morphological diversity through the early archosauromorph radiation. The Green Site, a rich deposit of predominantly fluvial, lacustrine, and floodplain sediments, lies within the Chinle Formation. The mud/sandstone matrix of the Green Layer contains abundant reptile, temnospondyl, chondrichthyan, and actinopterygian material. Biostratigraphy and constraints from uranium-lead dating of detrital zircons place the deposition of the Green Site locality approximately 216 Ma in the early Revueltian holochronozone. Sediment was bulk-sampled from a freshly exposed outcrop, and all teeth were picked individually, after screen washing through a series of different sized sieves. Picked teeth were divided into dozens of morphotypes, delineated by shape rather than taxonomy. Morphotypes were then quantified using a combination of 14 discrete and three continuous variables to evaluate differences in shape and other features (e.g., serration shape and density). An in-line/offset mesial carina factors heavily into the differentiation of these morphotypes These variables allow us to differentiate morphotypes quantifiably and repeatably. Morphotype data were visualized using non-metric multidimensional scaling and compared temporally to an assemblage from the Middle Triassic of Tanzania on bivariate plots. An expansion of occupied morphospace on these graphs illustrates a diversification of function and a differentiation of diet from the Middle to the Late Triassic, a timeline that postdates the Early Triassic archosauromorph taxonomic radiation. The quantification of dental morphology within the Late Triassic assemblage lays the groundwork for future research into ontogenetic sequences, heterodonty, homodonty, and taxonomic relations within this assemblage. The comparative methodology and results provide the scaffolding for future comparison to other assemblages that may differ temporally, spatially, environmentally. This research produces a more comprehensive picture of tooth differentiation during the Triassic archosauromorph radiation, and lays the necessary foundation for future work.
Date Awarded
Spring 2023
Department
Geology
Advisor 1
Rowan Lockwood
Recommended Citation
Clarke, Edward, "Distinguishing tooth morphotypes from a microvertebrate assemblage from the Chinle Formation (Late Triassic, Arizona) helps chronicle ecological differentiation of archosauromorphs" (2023). Geology Senior Theses. William & Mary. Paper 46.
https://scholarworks.wm.edu/geologyseniors/46
