Avian ancestors: a review of the phylogenetic relationships of the theropods Unenlagiidae, Microraptoria, Anchiornis, and Scansoriopterygidae

AGNOLIN, FEDERICO L.; NOVAS, FERNANDO E.

Springer Verlag

Año: 2013 p. 99

978-94-007-5636-6

Although consensus exists among authors that birds evolved from coelurosauriantheropods, paleontologists still debate the identification of the group of coelurosauriansthat most closely approaches the common ancestor of birds. The past20 years witnessed the discovery of a wide array of avian-like theropods that hasconsiderably amplified the anatomical disparity among deinonychosaurians, someof which resemble Archaeopteryx more than Deinonychus. Among these newlydiscovered theropods that show remarkable bird-like characteristics are the fourwingedtheropods Microraptor and Anchiornis, and the unenlagiids Unenlagia,Buitreraptor, and Rahonavis. Xiaotingia, Anchiornis, and Archaeopteryx areregarded as more nearly related to birds, rather than to Dromaeosauridae orTroodontidae. Moreover, a bizarre group of minute-sized coelurosaurs, theScansoriopterygidae, also exhibits some avian similarities that lead some authorsto interpret them as more closely related to birds than other dinosaurs. With theaim to explore the phylogenetic relationships of these coelurosaurians and birds,we merged recently published integrative databases, resulting in significantchanges in the topological distribution of taxa within Paraves. We present evidencethat Dromaeosauridae, Microraptoria, Unenlagiidae, and Anchiornis + Xiaotingiaform successive sister taxa of Aves, and that the Scansoriopterygidae are basalcoelurosaurians not closely related to birds. The implications in the evolutionarysequence of anatomical characters leading to birds, including the origin of flight,are also considered in light of this new phylogenetic hypothesis.