title: Dinosaur evolution. Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds.
abstract: Recent discoveries have highlighted the dramatic evolutionary transformation of massive, ground-dwelling theropod dinosaurs into light, volant birds. Here, we apply Bayesian approaches (originally developed for inferring geographic spread and rates of molecular evolution in viruses) in a different context: to infer size changes and rates of anatomical innovation (across up to 1549 skeletal characters) in fossils. These approaches identify two drivers underlying the dinosaur-bird transition. The theropod lineage directly ancestral to birds undergoes sustained miniaturization across 50 million years and at least 12 consecutive branches (internodes) and evolves skeletal adaptations four times faster than other dinosaurs. The distinct, prolonged phase of miniaturization along the bird stem would have facilitated the evolution of many novelties associated with small body size, such as reorientation of body mass, increased aerial ability, and paedomorphic skulls with reduced snouts but enlarged eyes and brains.
authors.affiliation: Earth Sciences Section, South Australian Museum, North Terrace, Adelaide 5000, Australia. School of Earth and Environmental Sciences, University of Adelaide 5005, Australia. mike.lee@samuseum.sa.gov.au.
authors.forename: Michael S Y
authors.initials: MS
authors.lastname: Lee
authors.affiliation: Museo Geologico e Paleontologico "Giovanni Capellini," Via Zamboni 63, 40126 Bologna, Italy. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Alma Mater Studiorum Università di Bologna, 40126 Bologna, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cau
authors.affiliation: Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK.
authors.forename: Darren
authors.initials: D
authors.lastname: Naish
authors.affiliation: Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK. MTA-DE Lendület Behavioural Ecology Research Group, Department of Evolutionary Zoology and Human Biology, University of Debrecen, 4032 Debrecen, Egyetem tér 1, Hungary.
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Dyke
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology*; D049628:Body Size; D025061:Dinosaurs / Q000033:anatomy & histology*