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We describe the tenth skeletal specimen of the Upper Jurassic Archaeopterygidae. The almost complete and well-preserved skeleton is assigned to Archaeopteryx siemensii Dames, 1897 and provides significant new information on the osteology of the Archaeopterygidae. As is evident from the new specimen, the palatine of Archaeopteryx was tetraradiate as in non-avian theropods, and not triradiate as in other avians. Also with respect to the position of the ectopterygoid, the data obtained from the new specimen lead to a revision of a previous reconstruction of the palate of Archaeopteryx. The morphology of the coracoid and that of the proximal tarsals is, for the first time, clearly visible in the new specimen. The new specimen demonstrates the presence of a hyperextendible second toe in Archaeopteryx. This feature is otherwise known only from the basal avian Rahonavis and deinonychosaurs (Dromaeosauridae and Troodontidae), and its presence in Archaeopteryx provides additional evidence for a close relationship between deinonychosaurs and avians. The new specimen also shows that the first toe of Archaeopteryx was not fully reversed but spread medially, supporting previous assumptions that Archaeopteryx was only facultatively arboreal. Finally, we comment on the taxonomic composition of the Archaeopterygidae and conclude that Archaeopteryx bavarica Wellnhofer, 1993 is likely to be a junior synonym of A. siemensii, and Wellnhoferia grandis Elżanowski, 2001 a junior synonym of A. lithographica von Meyer, 1861. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 149, 97–116.