892
Journal of Paleontology 89(5):882–893
demonstrate that the muscles necessary for performing a power stroke during pelvic paddling were extensive. The more abducted orientation of its femur suggests increased maneu- verability of the hip joint and likely gave it different hydrodynamics than R. domandaensis. Features of the vertebral column demonstrate that R. afer was not suited to utilize dorsoventral undulation of lumbar, sacral, and anterior caudal
vertebrae for propulsion, yet the increased degree of passive flexibility in the lumbar region would have facilitated an increase in the length of its power stroke during pelvic paddling due to increased sagittal bending. This would have increased the thrust generated during each stroke cycle. In sum, these characteristics indicate that R. afer was a more efficient and maneuverable foot-powered swimmer than R. domandaensis.
Acknowledgments
We are grateful to W. J. Sanders for preparation of CGM 42190 and the other remingtonocetid specimens discussed here. We thank M. D. Uhen, A. Berta, and two anonymous reviewers for helpful comments and suggestions on earlier versions of this manuscript. C.W. Thompson and J. G. M. Thewissen provided access to comparative specimens. This research was supported by the Calvin College Biology Department, the Egyptian Environmental Affairs Agency, and grant EAR-0920972 from the U.S. National Science Foundation.
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