A new perspective on the systematics and paleobiogeography of arvicoline rodents and the first radiometric age of the fauna from Cumberland Bone Cave, Maryland




Withnell, Charles Blaine

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Arvicoline rodents (voles, lemmings, and muskrats) are important taxa for characterizing and defining the North American Land Mammal Ages (NALMAs) of the Pliocene and Pleistocene. They are the basis for finer-scale temporal and spatial resolution and have been used to generate the divisions of the Blancan and Irvingtonian NALMAs. The profuse fossil record of arvicolines has never been reconciled with modern phylogenetic techniques, because the fossil record is almost exclusively isolated teeth or tooth-bearing elements. Here I present the most taxonomically robust (n=134) and genetically well sampled (n=5 genes) molecular phylogeny of arvicoline rodents. I used Parsimony, Maximum Likelihood, and Bayesian Inference methodologies to explore the systematic relationships of the clade. Seven fossil calibrations were used to place a series of temporal constraints on the tree to generate the first time-calibrated phylogeny of arvicoline rodents and I found that the clade originated in the Miocene at 6.5 Ma. This hypothesis was subsequently used to model speciation rates, and the patterns of paleobiogeography of the group in the R program BioGeoBEARS. I hypothesize that arvicoline rodents originated in Asia and that dispersal was asymmetric from west (Asia) to east (North America) with at least nine dispersal events between the two continents. My data indicate an origination of Lemmiscus at 5 Ma and the origination of the Synaptomys clade at 3.8 Ma, which supports previously problematic reports of both taxa from Hagerman, ID. This leaves the Blancan V division (as previously defined by the immigration of Synaptomys at 2.5 Ma) undefined and this leaves the Blancan undifferentiated from 4. Ma to the start of the Irvingtonian at 1.9 Ma. This is a novel approach of reconciling biochronology and probabilistic paleobiogeography. I also obtained the first radiometric age of the fauna of Cumberland Bone Cave using a combined Uranium Series and Electron Spin Resonance (ESR) approach, the first date of a middle Pleistocene site in Northeastern North America. Results indicate an age of the fauna of 756 +87/-98 ka which provides an important temporal anchor point from which to begin to understand the faunal dynamics of the region during the Pleistocene.


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