title: A basal dromaeosaurid and size evolution preceding avian flight.
abstract: Fossil evidence for changes in dinosaurs near the lineage leading to birds and the origin of flight has been sparse. A dinosaur from Mongolia represents the basal divergence within Dromaeosauridae. The taxon's small body size and phylogenetic position imply that extreme miniaturization was ancestral for Paraves (the clade including Avialae, Troodontidae, and Dromaeosauridae), phylogenetically earlier than where flight evolution is strongly inferred. In contrast to the sustained small body sizes among avialans throughout the Cretaceous Period, the two dinosaurian lineages most closely related to birds, dromaeosaurids and troodontids, underwent four independent events of gigantism, and in some lineages size increased by nearly three orders of magnitude. Thus, change in theropod body size leading to flight's origin was not unidirectional.
authors.affiliation: Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, USA. turner@amnh.org
authors.forename: Alan H
authors.initials: AH
authors.lastname: Turner
authors.forename: Diego
authors.initials: D
authors.lastname: Pol
authors.forename: Julia A
authors.initials: JA
authors.lastname: Clarke
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Erickson
authors.forename: Mark A
authors.initials: MA
authors.lastname: Norell
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology; D049628:Body Size; D001842:Bone and Bones / Q000033:anatomy & histology; D025061:Dinosaurs / Q000033:anatomy & histology / Q000145:classification; D005426:Flight, Animal; D005580:Fossils; D008986:Mongolia; D010802:Phylogeny