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Journal of Mammalian Evolution

, Volume 21, Issue 2, pp 223–241 | Cite as

Skeletal Morphology of Palaeocastor peninsulatus (Rodentia, Castoridae) from the Fort Logan Formation of Montana (early Arikareean): Ontogenetic and Paleoecological Interpretations

  • Jonathan Jean-Michel Calede
Original Paper

Abstract

Palaeocastorine beavers were diverse members of the burrowing fauna of the Oligocene of North America best known from the Great Plains and the Great Basin. Palaeocastorines are also found in the northern Rocky Mountains. Several specimens of Capacikala, Euhapsis, and Palaeocastor have been reported from Montana within the Cabbage Patch beds fauna. New occurrences of palaeocastorine beavers from the Fort Logan Formation of central Montana show that the fauna there included Palaeocastor fossor, Capacikala sp., Palaeocastor sp., and three specimens of a species previously known only from the John Day Formation of Oregon: Palaeocastor peninsulatus. The three specimens include crania and associated postcrania forming an ontogenetic series from a juvenile to a mature adult. Careful examination of these specimens shows that morphological changes throughout ontogeny are associated with increased burrowing ability in adults. Palaeocastor peninsulatus is a scratch-digger with few cranial adaptations to burrowing susceptible to change with maturity. Dental characters, however, are modified with wear and vary greatly across individuals of similar wear stage. Cranial morphology thus appears to be a reliable source of taxonomic information in palaeocastorines unlike dental material. These new specimens provide evidence for increased chisel-tooth digging in adults compared to juveniles as is observed throughout the evolution of palaeocastorines. This study demonstrates the need for future work focusing on intraspecific variation to help better define species boundaries among palaeocastorines and improve phylogenetic analyses.

Keywords

Fossoriality Systematics Palaeocastorinae Intraspecific variation 

Notes

Acknowledgments

I would like to thank J. Samuels and C. Schierup (JODA) as well as R. Eng and J. Bradley (UWBM) for access to specimens. G. Wilson provided space and equipment for research and commented on earlier versions of this paper. I thank J. Samuels for helpful discussions and for sharing his data on fossorial beavers. M. Chen, D. DeMar, W. Kehl, and L. DeBey provided feedback on earlier versions of the manuscript. N. Rybczynski provided her published matrix and advice on the phylogenetic analysis. A. Huttenlocker and L. Tsuji provided help with the phylogenetic analysis. P. Holroyd (UCMP) provided collection data. Two anonymous reviewers and the editor provided very helpful comments on earlier versions of the manuscript.

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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  1. 1.Department of BiologyUniversity of WashingtonSeattleUSA

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