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Jurassic crocodiles and killer whales

Posted by John Jackson on Dec 17, 2012 5:57:19 PM

Lorna Steel and collaborators have produced a paper that shows that modern-day killer whales are adapted to use the same hunting and feeding mechanisms as ancient crocodiles from more than a hundred million years ago.


They discovered that two crocodylians that grew to over 4m long and swam in Britain's shallow seas around 150 million years ago, were adapted to eat  prey similar to that of modern-day killer whales. Dakosaurus and Plesiosuchus both had robustly-built skulls and their anatomy indicates the capability to deliver great biting force.



Reconstructions showing the maximum body lengths for the Geosaurini genera present in the late Kimmeridgian-early Tithonian of Western Europe. 

The species from top to bottom are: Geosaurus giganteus, Dakosaurus maximus, Torvoneustes carpenteri and Plesiosuchus manselii. The maximum known body lengths of Torvoneustes and Geosaurus are from Young et al. [14], while those of Dakosaurus and Plesiosuchus are from this paper. The human diver is 1.8 m in height. All metriorhynchid life reconstructions are by Dmitry Bogdanov.  From Young et al. (2012) Creative Commons Attribution License for image and caption.


What is of particular interest is the parallel with the two types of North Atlantic killer whale: one smaller type which eats mainly fish prey, often by suction, and which has extensive wear and breakage on the teeth. The second larger type has little tooth breakage and eats other cetaceans. 


In the ancient crocodylians, there is extensive evidence for a similar dichotomy - in short Plesiosuchus is larger and shows little dental wear, with a wide effective gape that allowed many teeth to come into contact with the prey, so likely to be a specialist feeding on other marine reptiles. Dakosaurus was smaller, with considerable tooth wear and a shortened tooth row, suggesting a more general diet of smaller prey and suction feeding.  This difference in prey helps to explain how two large predators coexisted by avoiding competition.

Young, M.T., Brusatte, S.L., Brandalise de Andrade, M., Desojo, J.B., Beatty, B.L., STEEL, L., Fernandez, M.S., Sakamoto, M., Ruiz-Omenaca, J.I., & Schoch, R., 2012. The Cranial Osteology and Feeding Ecology of the Metriorhynchid Crocodylomorph Genera Dakosaurus and Plesiosuchus from the Late Jurassic of Europe. PLoS ONE 7(9): e44985. doi:10.1371/journal.pone.0044985

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