A New basal Archosauriform Diapsid from the Lower Triassic of Argentina.

Martín D. Ezcurra, Agustina Leucona and Agustín Martinelli

The best-known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reported by José Bonaparte in 1981, collected from the Quebrada de los Fósiles Formation (Puesto Viejo Group, Argentina). This specimen consists of well-preserved natural external molds of a partial postcranium that preserve dorsal vertebrae, osteoderms, a dorsal rib, a possible gastralium, a chevron, a humerus, an ilium, two metapodials, ungual. Were-describe this specimen and identify autapomorphies that allow us to recognize Koilamasuchus gonzalezdiazi, gen. et sp. nov. The presence of an iliac blade with a slightly convex dorsal margin and with a maximum length more than 3 times its maximum height places Koilamasuchus within Archosauriformes. A cladistic analysis of basal Archosauriformes positions Koilamasuchus more crownwards than Proterosuchus, Sarmatosuchus, Fugusuchus, and Osmolskina, as the sister taxon of the clade that includes Erythrosuchidae and Archosauria. Proterosuchidae is found to be paraphyletic. The presence of an iliac preacetabular process, a pubic peduncle that forms an angle lower than 45◦ to the longitudinal axis of the ilium, and dorsal body osteoderms positions Koilamasuchus in Archosauriformes more crownwards than proterosuchids. Koilamasuchus is more basal than erythrosuchids within Archosauriformes because of the presence of dorsal ribs with a poorly developed proximal end. Koilamasuchus importantly increases the diversity of Archosauriformes during the biotic recovery following the Permo-Triassic mass extinction.

Ezcurra, M.D., Leucona, A. and Martinelli, A., 2010. A New Basal Achosauriform Diapsid from the Lower Triassic of Argentina. Journal of Vertebrate Paleontology 30(5):1433–1450.

New information on the cranial and vertebral anatomy of Buitreraptor gonzalezorum (Theropoda, Unenlagiinae) and preliminary comparisons with other South American unenlagiines

F.A. GIanechini, S. Apesteguía and P.J. Makovicky

Within the framework of a doctoral thesis about the small theropods coming from the Cerro Policía area (Candeleros Formation, Río Negro Province), novel information of Buitreraptor gonzalezorum Makovicky, Apesteguía and Agnolín 2005 is presented here, including partial comparisons with other unenlagiines. Shared cranial characters between Buitreraptor and Austroraptor cabazai Novas, Pol, Canale, Porfiri and Calvo 2009 include: skull exceeding femoral length by 25%; low anterior process of maxilla; large maxillary fenestra not dorsally displaced; more than twenty maxillary and dentary teeth; fluted teeth without serrations and without basal constriction; groove on the dentary containing a row of nutrient foramina. Otherwise, Buitreraptor differs from Austroraptor in having a larger maxillary fenestra; elongated frontals with dorsal depressions; triangular postorbital; compressed teeth, with an 8-shaped basal section. Concerning vertebral features, Buitreraptor has a ventral faint keel on the axis (not comparable with other unenlagiines); elongated medial cervicals; epipophyses on all cervicals; carotid process on the latest cervicals; ventrolateral ridges on the last cervical culminating posteriorly as small tubers; neural spines of the dorsals without distal spine tables (this latter feature invalidates a proposed synapomorphy for Unenlagiinae). Additionally, whereas pleurocoels are restricted to anterior dorsals in Buitreraptor (and probably in Austroraptor), in Unenlagia comahuensis Novas and Puerta 1997 they are in anterior and posterior dorsals; and the foramina that pierces the base of the neural spines in the latter are absent in the two former. This analysis increases the knowledge of the anatomy of Buitreraptor and shows a high internal variability among unenlagiines

Fuente: XXV Jornadas Argentinas de Paleontología de Vertebrados, San Luis, 2010.

Primitive broad-crowned titanosaurs

Primitive broad-crowned titanosaurs in the Uppermost Cretaceous?

P.A. Gallina, S. Apesteguía and F.A. Gianechini

Despite several tooth morphologies were recognized in sauropods, it is widely accepted that macronarians exhibit two main morphotypes: broad-crowned teeth and narrow-crowned teeth. The former, spoon-shaped and provided of a main axis and two lateral flanges, is present in basal forms like Camarasaurus Cope. Conversely, the latter, with reduced flanges, is considered as characteristical for derived titanosaurs, notwithstanding this ―narrow tooth concept actually masks a hidden diversity of morphologies (i.e., cylindrical, hexagonal prisms, and double-ridged). Otherwise, the diversity of Upper Cretaceous dental morphotypes includes also two broader forms. One is represented by broad, distally acuminated, labiolingually compressed, and spatulated crowns, similar but much lesser than that of Camarasaurus Cope, and present in undoubted titanosaurs like Ampelosaurus Le Loeuff from France. The other is represented by labiolingually compressed and distally acuminated teeth with a D-shaped crown slightly broader than the root, and both lingual and lateral high-angled wear facets that resembles those of basal titanosauriforms (e.g., Brachiosaurus Riggs). This type is well represented in Argentina, as show the teeth from the Arroyo Morterito (Salta, PVL 3670-12), some smaller teeth from Los Alamitos Formation (MACN 1133RN), isolated tooth from the Allen Formation (MMRM-PV 53). The presence of this kind of teeth in Campanian-Maastrichtian strata can be attributed both to the presence of surviving basal titanosaurian lineages and/or, the preservation of plesiomorphical traits in the dental morphology of late lineages like the Saltasaurinae.
Fuente: XXV Jornadas Argentinas de Paleontología de Vertebrados, San Luis, 2010.
Foto: solo a modo ilustrativo.

A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny

Martin D. Ezcurra

It was traditionally thought that the oldest known dinosaur assemblages were not diverse, and that their early diversificationband numerical dominance over other tetrapods occurred during the latest Triassic. However, new evidence gathered from the lower levels of the Ischigualasto Fm. of Argentina challenges this view. New dinosaur remains are described from this stratigraphical unit, including the new species Chromogisaurus novasi. This taxon is distinguished from other basal dinosauriforms by the presence of proximal caudals without median notch separating the postzygapophyses, femoral lateral surface with deep and large fossa immediately below the trochanteric shelf, and metatarsal II with strongly dorsoventrally asymmetric distal condyles. A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus. Such an affinity is for the first time suggested for Guaibasaurus, whereas Panphagia is not recovered as the most basal sauropodomorph. Furthermore, Chromogisaurus is consistently located as more closely related to Saturnalia than to any other dinosaur. Thus, the Saturnalia + Chromogisaurus clade is named here as the new subfamily Saturnaliinae. In addition, Eoraptor is found to be the sister-taxon of Neotheropoda, and herrerasaurids to be non-eusaurischian saurischians. The new evidence presented here demonstrates that dinosaurs first appeared in the fossil record as a diverse group, although they were a numerically minor component of faunas in which they occur. Accordingly, the early increase of dinosaur diversity and their numerical dominance over other terrestrial tetrapods were diachronous processes, with the latter preceded by a period of low abundance but high diversity.

Ezcurra, M.D. 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny. Palaeontology, 8: 3, 371-425