title: Live birth in an archosauromorph reptile.
abstract: Live birth has evolved many times independently in vertebrates, such as mammals and diverse groups of lizards and snakes. However, live birth is unknown in the major clade Archosauromorpha, a group that first evolved some 260 million years ago and is represented today by birds and crocodilians. Here we report the discovery of a pregnant long-necked marine reptile (Dinocephalosaurus) from the Middle Triassic (∼245 million years ago) of southwest China showing live birth in archosauromorphs. Our discovery pushes back evidence of reproductive biology in the clade by roughly 50 million years, and shows that there is no fundamental reason that archosauromorphs could not achieve live birth. Our phylogenetic models indicate that Dinocephalosaurus determined the sex of their offspring by sex chromosomes rather than by environmental temperature like crocodilians. Our results provide crucial evidence for genotypic sex determination facilitating land-water transitions in amniotes.
authors.affiliation: School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China.|Chengdu Center, China Geological Survey, Chengdu 610081, China.|State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, CAS, Nanjing 210008, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Earth Sciences, Montana State University, Bozeman, Montana 59717, USA.
authors.forename: Chris L
authors.initials: CL
authors.lastname: Organ
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Benton
authors.affiliation: School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Brandley
authors.affiliation: School of Earth and Environmental Sciences, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Jonathan C
authors.identifier: 0000-0002-3659-5849
authors.initials: JC
authors.lastname: Aitchison
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002681:China; D025061:Dinosaurs / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D005260:Female; D005580:Fossils; D050498:Live Birth; D008386:Marine Biology; D010802:Phylogeny; D011247:Pregnancy; D012104:Reptiles / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D012723:Sex; D012730:Sex Chromosomes; D019849:Sex Determination Processes; D013696:Temperature