Biogeography of Arikareean mammalian communities

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As part of my dissertation, I am interested in studying the biogeographic relationships between Arikareean deposits in the northern United States (Oregon, Montana, Nebraska, Wyoming, and South Dakota). As part of a statistics class at the University of Washington, I have started investigating taxonomic similarities across Arikareean faunas using (in part) ordination methods.

These initial results are published in an in-house journal:

Calede, J. 2012. Biogeography and endemism in Arikareean faunas (North America, 30-18.8 Ma). Electronic Journal of Applied Multivariate Statistics 4:12–22.

You can read the abstract below:

The rich and geographically widespread Arikareean fossil record (North America, 30 to 18.8 Ma) provides a unique opportunity to test hypothesis of geographic clusters and gradients in faunal composition. I use multivariate statistics (cluster analysis and ordinations) to test the hypotheses that early modern mammalian faunas of the Arikareean were significantly different across biogeographic regions, were arranged along geographic gradients and that this apparent biogeographic pattern cannot be accounted for by the incomplete nature of the fossil record. The results show that there is support for a biogeographic structure of Arikareean communities with some possibly endemic assemblages (Cabbage Patch Beds of western Montana, Delaho Formation of southwestern Texas). The fossil assemblages reflect a strong longitudinal gradient. No evidence for a latitudinal gradient is found. Neither age nor sampling seem to influence the observed pattern which instead is correlated with depositional environment. This suggests that much of the observed faunal differences across assemblages and regions can be explained by habitats constraining local and regional faunas. Further study exploring the functional diversity of these assemblages will further investigate the controls on community assembly during the late Oligocene-earlyMiocene.

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