Comparison of Miocene to early Pleistocene-aged Castor californicus (Rodentia: Castoridae) to extant beavers and implications for the evolution of Castor in North America

The beaver, genus Castor, is represented in North America today by Castor canadensis and in Eurasia by C. fiber. Historically, the fossil Miocene to early Pleistocene-aged North American beaver C. californicus has been considered a distinct species from C. canadensis due to its larger size. In this study, we test the hypothesis that the morphology of Miocene to early Pleistocene-aged fossils of C. californicus differs from that of the extant C. canadensis. Specimens of fossil and extant Castor were compared using 2D geometric morphometrics of skull and dentary material and linear measurements of postcranial material to analyze morphological differences between species and determine whether C. californicus fits within the range of intraspecific variation seen in C. canadensis. Results show that C. canadensis is highly variable in both skull and postcranial morphology, and C. californicus falls largely within the range of variation seen within the extant species. The morphological similarities between the two species suggest that they can be treated as ecological analogs and may represent change in a single species through time, although a rigorous evaluation of whether they are conspecific will require more data. Kelly E. Lubbers. The Mammoth Site, Hot Springs, South Dakota 57747, USA and Department of Geosciences, East Tennessee State University, Johnson City, Tennessee 37614, USA. kellyl@mammothsite.org Joshua X. Samuels. Department of Geosciences, East Tennessee State University, Johnson City, Tennessee 37614, USA and Don Sundquist Center of Excellence in Paleontology, East Tennessee State University, Johnson City, Tennessee, 37614, USA. samuelsjx@etsu.edu