Understanding the origin and early evolution of snakes from lizards depends on accurate morphological knowledge of the skull in basal lineages, but fossil specimens of archaic snakes have been rare, and either fragmentary or difficult to study as a result of compression by enclosing sediments1,2,3,4,5,6. A number of Cenozoic fossil snakes from Australia have vertebral morphology diagnostic of an extinct group, Madtsoiidae, that was widespread in Gondwana from mid-Cretaceous (Cenomanian) to Eocene times, and also reached Europe in the late Cretaceous period3,7,8,9,10,11. Despite this long history, only about half the skull is known from the best-known species Wonambi naracoortensis7,11,12,13, and the few known cranial elements of other species have added little further evidence for phylogenetic relationships10,14,15,16,17,18,19. Conflicting hypotheses have been proposed for their relationships and evolutionary significance, either as basal ophidians with many ancestral (varanoid- or mosasaur-like) features, or advanced (macrostomatan) alethinophidians of little relevance to snake origins3,4,7,11,12,13,14,15,20. Here I report two partial skeletons referred to Yurlunggur8, from the late Oligocene and early Miocene of northern Australia, which together represent almost the complete skull and mandible. The exceptionally preserved skulls provide new evidence linking Yurlunggur with Wonambi and other madtsoiids, falsifying predictions of the macrostomatan hypothesis, and supporting the exclusion of Madtsoiidae from the clade including all extant snakes.
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I thank M. Archer, H. Godthelp, A. Gillespie and K. Black (University of New South Wales (UNSW), Sydney) and B. Chambers (Riversleigh Fossil Centre, Mount Isa) for access to and initial preparation of Riversleigh fossils collected by the UNSW team; M. Lee, M. Hutchinson, T. Flannery and J. McNamara (South Australian Museum) for access to facilities and materials; and J.-C. Rage, Z. Szyndlar, M. Lee, M. Kearney, C. Davidson and E. Chitra for discussions and comments. Financial support was provided by the Australian Research Council and the Australian Geographic Society.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The author declares no competing financial interests.
This file contains Supplementary Data and Supplementary Methods in seven separate sections: 1) Revised diagnoses (of taxa Madtsoiidae and Yurlunggur); 2) Additional cranial material, and condition of skull QMF45391; 3) Morphological character list (modified from Lee and Scanlon 2002); 4) Data matrix (Nexus format); 5) Main analyses (parsimony, Bremer and bootstrap analyses in PAUP*); 6) Other analyses; 7) Additional references (those cited in SI but not in the print version of the paper). (DOC 798 kb)
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Scanlon, J. Skull of the large non-macrostomatan snake Yurlunggur from the Australian Oligo-Miocene. Nature 439, 839–842 (2006). https://doi.org/10.1038/nature04137
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