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The Pleistocene serpent Wonambi and the early evolution of snakes


The Madtsoiidae were medium sized to gigantic snakes with a fossil record extending from the mid-Cretaceous to the Pleistocene, and spanning Europe, Africa, Madagascar, South America and Australia1,2,3. This widely distributed group survived for about 90 million years (70% of known ophidian history), and potentially provides important insights into the origin and early evolution of snakes. However, madtsoiids are known mostly from their vertebrae, and their skull morphology and phylogenetic affinities have been enigmatic. Here we report new Australian material of Wonambi, one of the last-surviving madtsoiids4,5,6, that allows the first detailed assessment of madtsoiid cranial anatomy and relationships. Despite its recent age, which could have overlapped with human history in Australia, Wonambi is one of the most primitive snakes known—as basal as the Cretaceous forms Pachyrhachis7 and Dinilysia8. None of these three primitive snake lineages shows features associated with burrowing, nor do any of the nearest lizard relatives of snakes (varanoids). These phylogenetic conclusions contradict the widely held ‘subterranean’ theory of snake origins9,10,11,12, and instead imply that burrowing snakes (scolecophidians and anilioids) acquired their fossorial adaptations after the evolution of the snake body form and jaw apparatus in a large aquatic or (surface-active) terrestrial ancestor.

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Figure 1: Reconstruction of the skull of Wonambi naracoortensis Smith, 1976.
Figure 2: Selected elements of Wonambi exhibiting phylogenetically important characters.
Figure 3: Cladogram (strict consensus of two most parsimonious trees, each with length = 649, consistency index = 0.49, retention index = 0.66 ) showing relationships among snake lineages and the very basal position of madtsoiids.

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We thank D. J. Barrie, M. Archer, R. E. Molnar, N. Pledge and R. T. Wells for access to materials, and V. Wallach, G. Underwood, J.-C. Rage, D. J. Barrie, S. E. Evans, H. W. Greene, D. Cundall, M. W. Caldwell and A. G. Kluge for discussion. This research was supported by Australian Research Council grants to M.L. and J.S. Work at Riversleigh was supported by the Australian Research Council and University of New South Wales (to M. Archer), and work at Naracoorte by Flinders University, the South Australian Museum, L. and G. Henschke, the Barrie family and numerous volunteers.

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Correspondence to John D. Scanlon.

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Scanlon, J., Lee, M. The Pleistocene serpent Wonambi and the early evolution of snakes . Nature 403, 416–420 (2000).

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