Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs

• Autores: Bittencourt, Jonathas S.; Arcucci, Andrea Beatriz; Marsicano, Claudia Alicia; Langer, Max C.
• Año de publicación: 2014
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Lewisuchus; Pseudolagosuchus; Dinosauriformes; Middle Triassic
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

Lewisuchus admixtus is an enigmatic early dinosauriform from the Chañares Formation, Ladinian of Argentina, which has been recently considered a member of Silesauridae. Yet, it differs markedly from Late Triassic silesaurids in dental and vertebral anatomy. Indeed, a detailed redescription of its holotype allowed the identification of several features of the skeleton previously unrecognized amongst silesaurids. These include pterygoid teeth, a dorsomedial posttemporal opening on the otoccipital, foramina associated with cranial nerves X–XII on the caudal region of the prootic–otoccipital, and postaxial neck/trunk vertebrae with craniocaudally expanded neural spines. The presence of a single row of presacral scutes was also confirmed. Some elements previously referred to, or found associated with, the holotype, including a lower jaw, pedal elements and an astragalus, more probably correspond to proterochampsid remains. The anatomical information available for the holotype of L. admixtus was rescored into a new phylogenetic dataset for dinosauromorphs, mostly based on previous works. Lewisuchus admixtus and Pseudolagosuchus major are treated as distinct OTUs because their preserved skeletons mostly lack overlapping parts. The parsimony analysis supports the basal position of L. admixtus within dinosauriforms, prior to the silesaurid–dinosaur split, rather than at the base of Silesauridae. This suggests that a higher number of early dinosauriform clades branched in the Middle and Late Triassic than previously suggested.
Fil: Bittencourt, Jonathas S.. Universidade Federal do Minas Gerais; Brasil
Fil: Arcucci, Andrea Beatriz. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Departamento de Bioquímica y Ciencias Biológicas. Area de Zoología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
Fil: Marsicano, Claudia Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos ; Argentina
Fil: Langer, Max C.. Universidade de Sao Paulo; Brasil