title: A palaeoequatorial ornithischian and new constraints on early dinosaur diversification.
abstract: Current characterizations of early dinosaur evolution are incomplete: existing palaeobiological and phylogenetic scenarios are based on a fossil record dominated by saurischians and the implications of the early ornithischian record are often overlooked. Moreover, the timings of deep phylogenetic divergences within Dinosauria are poorly constrained owing to the absence of a rigorous chronostratigraphical framework for key Late Triassic-Early Jurassic localities. A new dinosaur from the earliest Jurassic of the Venezuelan Andes is the first basal ornithischian recovered from terrestrial deposits directly associated with a precise radioisotopic date and the first-named dinosaur from northern South America. It expands the early palaeogeographical range of Ornithischia to palaeoequatorial regions, an area sometimes thought to be devoid of early dinosaur taxa, and offers insights into early dinosaur growth rates, the evolution of sociality and the rapid tempo of the global dinosaur radiation following the end-Triassic mass extinction, helping to underscore the importance of the ornithischian record in broad-scale discussions of early dinosaur history.
authors.affiliation: Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK p.barrett@nhm.ac.uk.
authors.forename: Paul M
authors.initials: PM
authors.lastname: Barrett
authors.affiliation: School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK GeoBio-Center, Ludwig-Maximilians-Universität München, Richard-Wagner-Straße 10, 80333 Munich, Germany.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Butler
authors.affiliation: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
authors.forename: Roland
authors.initials: R
authors.lastname: Mundil
authors.affiliation: Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, 8006 Zürich, Switzerland.
authors.forename: Torsten M
authors.initials: TM
authors.lastname: Scheyer
authors.affiliation: Natural History Museum of Utah, 301 Wakara Way, Salt Lake City, UT 84108-1214, USA Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112-0102, USA.
authors.forename: Randall B
authors.initials: RB
authors.lastname: Irmis
authors.affiliation: Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, 8006 Zürich, Switzerland.
authors.forename: Marcelo R
authors.initials: MR
authors.lastname: Sánchez-Villagra
mesh_terms: D000818:Animals; D005075:Biological Evolution; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000145:classification*; D005580:Fossils / Q000033:anatomy & histology*; D019015:Geologic Sediments; D010802:Phylogeny; D014687:Venezuela
keywords: Lower Jurassic; Ornithischia; end-Triassic extinction; osteohistology; palaeobiogeography
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