|Lumbar vertebrae in right lateral view. From left to right: "Eocetus" wardii (from Uhen 1999), Basiloterus hussaini, and Basilosaurus drazindai - note that the latter-most may be an anterior caudal (from Gingerich et al. 1997). For comparison: Basilosaurus isis vertebrae.|
|Lumbar vertebrae in anterior view. Ditto order.|
|Maiacetus inuus, a basal "protocetid" (Uhen 2011). From Wikipedia Commons.|
Protocetidae is a blatantly paraphyletic "family" of extinct cetaceans from Eocene coastal marine deposits with hip and femur morphology indicating amphibious capabilities (most of the time) and no evidence of flukes (Uhen 2010). Uhen (1999) appears to think that "Eocetus" wardii had weight-bearing hips, however Uhen (2010) refers to them as "moderately reduced" and regarded the species as possibly non-amphibious. This is perhaps not surprising since Eocetus, "Eocetus", and an unnamed Pisco Formation species are the sister group of Pelagiceti (Uhen et al. 2011). This could make them closer relatives of Dorudon than Maiacetus, and raises the question of how many typical protocetid traits they actually exhibited. Perhaps they were entirely aquatic tail-based swimmers which just happened to have fairly large vestigial legs.
|Dorudon atrox. From Wikipedia Commons.|
"Eocetus" wardii is clearly related to unnamed Pisco Formation material which exhibits the same distinctive traits (moderate centrum elongation, elongated neural arches and spines and transverse processes, strange pock-marked texture) with the only difference being that the unnamed material is 35% smaller (Uhen et al. 2011). The Egyptian vertebrae dubiously assigned to Eocetus schweinfurthi (figured in Uhen 1999) also seem quite similar (including the pock-marks), and if it is also a member of this clade, it would indicate a sizable trans-oceanic range. This in turn could be taken as evidence of the whales being largely pelagic... of course this is quite speculative.
There of course remains much to be known about these cetaceans, and perhaps future discoveries will be enlightening as to how similar they were to the pelagic cetaceans, as well as the origins of Pelagiceti. I really hope it turns out that a Basilosaurus-sized animal could walk on land.
Geisler, J. H., Sanders, A. E., and Luo, Z-X. (2005). A New Protocetid Whale (Cetacea: Archaeoceti) from the Late Middle Eocene of South Carolina. American Museum Novitates 3480, 1-65. Available.
Gingerich, P. D., Arif, M., Bhatti, M. A., Anwar, M., & Sanders, W. J. (1997). Basilosaurus drazindai and Basiloterus hussaini, new Archaeoceti (Mammalia, Cetacea) from the middle Eocene Drazinda Formation, with a revised interpretation of ages of whale-bearing strata in the Kirthar Group of the Sulaiman Range, Punjab (Pakistan). Contributions from the Museum of Paleontology, University of Michigan 30 (2), 55-81. Available.
Uhen, M. D., Pyenson, N. D., Devries, T. J., Urbina, M., and Renne, P. R. (2011). New middle Eocene whales from the Pisco Basin of Peru. Journal of Paleontology 85(5), 955-969. doi: http://dx.doi.org/10.1666/10-162.1
Uhen, M. D. (2010). The Origin(s) of Whales. Annual Review of Earth and Planetary Sciences 38, 189–221. Available.
Uhen, M. D. (2008). Basilosaurids. In: Perrin, W. F., Würsig, B., and Thewissen, J. G. M. (eds.) Encyclopedia of Marine Mammals, Second Edition. Elsevier: Burlington, Massachusetts. Available.
Uhen, M. D. (1999). New Species of Protocetid Archaeocete Whale, Eocetus wardii (Mammalia: Cetacea) from the Middle Eocene of North Carolina. Journal of Paleontology 73(3), 512-528.
Weems, R. E., Edwards, L. E., Osborne, J. E., and Alford, A. A. (2011). An occurrence of the protocetid whale "Eocetus" wardii in the Middle Eocene formation of Virginia. Journal of Paleontology 85(2), 271-278. Available.