Review of a basal archosauriform from the Early Triassic of the Puesto Viejo Group, Mendoza, Argentina


The clade Archosauriformes encloses the Archosauria and several Late Permian and Triassic stem-groups. These non-archosaur archosauriforms re well-known from the Early and Middle Triassic of North America, Europe, Asia, Oceania, and Africa, but its South American fossil record is mostly restricted to the endemic Middle and Late Triassic proterochampsids.Accordingly, the Early Triassic is an obscure period for the South American archosauriform history. At present, the only known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reported by Bonaparte in the 80’s, from the Quebrada de los Fósiles Formation (Puesto Viejo Group, Mendoza Province). This specimen (MACN-PV 18119) is based on well-preserved natural external moulds of a partial postcranium: dorsal vertebrae, osteoderms, dorsal rib, chevron, humerus, radius?, left ilium, and pedal ungual. Due to its importance, a review of the morphology and phylogenetic affinities of this specimen was undertaken. A cladistic analysis depi c t ed MACN-PV 18119 a s a ba s a l archosauriform more derived than proterosuchids due the presence of dorsal centra with lateral fossa below the neurocentral suture, preacetabular process on the iliac blade, and osteoderms. Nevertheless, the Argentine specimen was found as more basal than Euparkeria Broom, Erythrosuchus Broom, and more derived forms (e.g. Doswellia Weems, proterochampsids, archosaurs) by the absence of ribs with capitulum and tuberculum developed as distinct tubercles. Accordingly, MACN-PV 18119 represents a taxon which does not fit with the currently known lineages of non-archosaur archosauriforms (e.g. Proterosuchidae, Erythrosuchidae, “Euparkeriidae", Proterochampsidae), increasing the diversity of the group during the biotic recovery after the Permo- Triassic mass extinction event.

(1) Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". Buenos Aires, Argentina.
(2) Museo Paleontológico Egidio Feruglio. Trelew, Argentina.
(3) Laboratório de Geologia, Curso de Geografia, Campus do Pontal, Univ. Fed. de Uberlândia, Ituiutaba. Minas Gerais, Brasil.

XXIV Jornadas Argentinas de Paleontología de Vertebrados, San Rafael, Mendoza, Argentina. Mayo, 2009.