title: A new sphenodontian (Lepidosauria: Rhynchocephalia) from the Late Triassic of Argentina and the early origin of the herbivore opisthodontians.
abstract: Sphenodontians were a successful group of rhynchocephalian reptiles that dominated the fossil record of Lepidosauria during the Triassic and Jurassic. Although evidence of extinction is seen at the end of the Laurasian Early Cretaceous, they appeared to remain numerically abundant in South America until the end of the period. Most of the known Late Cretaceous record in South America is composed of opisthodontians, the herbivorous branch of Sphenodontia, whose oldest members were until recently reported to be from the Kimmeridgian-Tithonian (Late Jurassic). Here, we report a new sphenodontian, Sphenotitan leyesi gen. et sp. nov., collected from the Upper Triassic Quebrada del Barro Formation of northwestern Argentina. Phylogenetic analysis identifies Sphenotitan as a basal member of Opisthodontia, extending the known record of opisthodontians and the origin of herbivory in this group by 50 Myr.
authors.affiliation: Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, , Avenida España 400 Norte, 5400 San Juan, Argentina, Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, , Buenos Aires, Argentina.
authors.forename: Ricardo N
authors.initials: RN
authors.lastname: Martínez
authors.forename: Cecilia
authors.initials: C
authors.lastname: Apaldetti
authors.forename: Carina E
authors.initials: CE
authors.lastname: Colombi
authors.forename: Angel
authors.initials: A
authors.lastname: Praderio
authors.forename: Eliana
authors.initials: E
authors.lastname: Fernandez
authors.forename: Paula
authors.initials: P
authors.lastname: Santi Malnis
authors.forename: Gustavo A
authors.initials: GA
authors.lastname: Correa
authors.forename: Diego
authors.initials: D
authors.lastname: Abelin
authors.forename: Oscar
authors.initials: O
authors.lastname: Alcober
mesh_terms: D000818:Animals; D001118:Argentina; D005075:Biological Evolution; D005580:Fossils; D060434:Herbivory; D007568:Jaw / Q000033:anatomy & histology; D010802:Phylogeny; D012104:Reptiles / Q000033:anatomy & histology* / Q000145:classification* / Q000502:physiology; D012886:Skull / Q000033:anatomy & histology; D013131:Spine / Q000033:anatomy & histology
keywords: Argentina; Lepidosauria; Opisthodontia; Sphenodontia; Upper Triassic