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Phylogenetic relationships of the basal dinosaurs, the Herrerasauridae

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Abstract

Herrerasaurids were predatory, obligatorily bipedal dinosaurs recorded in early Late Triassic rocks of South America. It has been suggested recently that the Herrerasauridae constitute a paraphyletic assemblage, but several apomorphic traits in the dorsal, sacral, and caudal vertebrae and the pectoral and pelvic girdles support the monophyly of this group. The relationships of Dinosauria with other members of Ornithodira are considered, supporting the monophyly of the newly recognized clade Dinosauriformes. The Dinosauria, including Herrerasauridae, Saurischia, and Ornithischia, is diagnosed on the basis of six synapomorphic traits. The hypothesis that the Herrerasauridae constitute the sister-group of the remaining dinosaurs is supported here on the basis of four apomorphic traits uniquely shared by Saurischia and Ornithischia. -from Author
... A423. Sacral vertebrae, primordial sacral vertebrae, depth of the iliac articular surface relative to the depth of the ilium (Novas, 1992;Yates, 2007a;. ...
... A442. Anterior caudal vertebrae, neural spines, orientation of posterior margin: sloping posterodorsally (0), vertical (1) (Novas, 1992;. ...
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Non-sauropod sauropodomorphs, also known as 'basal sauropodomorphs' or 'prosauropods', have been thoroughly studied in recent years. Several hypotheses on the interrelationships within this group have been proposed, ranging from a complete paraphyly, where the group represents a grade from basal saurischians to Sauropoda, to a group on its own. The grade-like hypothesis is the most accepted; however, the relationships between the different taxa are not consistent amongst the proposed scenarios. These inconsistencies have been attributed to missing data and unstable (i.e., poorly preserved) taxa, nevertheless, an extensive comparative cladistic analysis has found that these inconsistencies instead come from the character coding and character selection, plus the strategies on merging data sets. Furthermore, a detailed character analysis using information theory and mathematical topology as an approach for character delineation is explored here to operationalise characters and reduce the potential impact of missing data. This analysis also produced the largest and most comprehensive matrix after the reassessment and operationalisation of every character applied to this group far. Additionally, partition analyses performed on this data set have found consistencies in the interrelationships within non-sauropod Sauropodomorpha and has found strong support for smaller clades such as Plateosauridae, Riojasauridae, Anchisauridae, Massospondylinae and Lufengosarinae. The results of these analyses also highlight a different scenario on how quadrupedality evolved, independently originating twice within the group, and provide a better framework to understand the palaeo-biogeography and diversification rate of the first herbivore radiation of dinosaurs.
... Coria y Rodríguez (1993) ponen en duda esa asignación y proponen a Xenotarsosaurus como un Neoceratosauria incertae sedis. Sin embargo, Novas (1992), Carrano y Sampson (2008) y Ezcurra y Novas (2016), entre otros, mantienen al terópodo bajobarrealense como integrante de la familia Abelisauridae. Aunque, desde su descripción original nuevos miembros del clado han sido descriptos, los restos preservados, particularmente el fémur ( Fig. 10A) y tibia y fíbula ( Fig. 10B) de Xenotarsosaurus, son similares a estos nuevos representantes. ...
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En la cuenca del Golfo San Jorge se encuentran unidades de origen continental reunidas en el Grupo Chubut (Barreamiano-Maastrichtiano) que son portadoras de un alto contenido fosilífero. Este registro paleontológico de vertebrados continentales cretácicos de la cuenca es una de los más diversos de América del Sur. Es relativamente escaso al momento en la Formación Matasiete (Aptiano), pero mucho más abundante en las formaciones Bajo Barreal (Cenomaniano temprano-Turoniano tardío) y Lago Colhué Huapi (Conianciano-Maastrichtiano). Incluye una importante cantidad de grupos de vertebrados, destacándose los dinosaurios saurópodos, terópodos y ornitópodos. También están bien documentados otros taxones como cocodrilos y tortugas, pero son escasos hasta el momento los restos de reptiles voladores, anuros y peces. Muchos de los hallazgos son de gran importancia y han contribuido al conocimiento de diferentes grupos y de sus relaciones filogenéticas y paleobiogeográficas. Se describe en este trabajo, solo el registro paleontológico más relevante y especies válidas conocidas hasta el momento.
... Dinosauriformes Novas, 1992. Dinosauria Owen, 1842. ...
Article
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... The proximal surface is crushed between the posterior condyles and cnemial crest. The cnemial crest projects straight anteriorly as it does in dinosauromorphs (Novas 1992:4-1, Nesbitt 2011 such as Dromomeron romeri Nesbitt et al. (2007, GR 220) (Nesbitt et al. 2009b: fig. 4c) and D. gregorii Nesbitt et al. (2009b, TMM 31100-278: fig. ...
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Dinosauromorph specimens from Petrified Forest National Park have been recovered from four major collecting efforts since 1982, including the most recent paleontological inventory of new park lands acquired in 2011. Additionally, an emphasis on understanding the stepwise acquisition of character traits along the dinosaurian lineage has helped identify previously collected specimens in museum collections. Here we briefly describe and use apomorphies to identify 32 additional dinosauromorph specimens found at Petrified Forest National Park, bringing the total number of dinosauromorph specimens presently known from the park to 50, a 600% increase since the year 2000. These specimens are all Norian in age and come from the Blue Mesa Member, Sonsela Member, and Petrified Forest Member of the Chinle Formation. These include the proximal end of a tibia that represents the oldest unambiguous dinosaur specimen from the Chinle Formation. We then contextualize these specimens with the dinosauromorph assemblages from the Norian of Utah, Colorado, New Mexico, and Texas, as well as the Carnian and Norian dinosauromorph assemblages from South America, Africa, and Europe. Despite increased sampling we still find no evidence for sauropodomorph and ornithischian dinosaurs in Western North America. An increase in sampling, combined with the use of apomorphies to identify collected specimens, will continue to improve the global dinosauromorph fossil record that can be used to answer questions on biochronology and the evolutionary history of the avian lineage.
... Moreover, an early diverging phylogenetic position within Saurischia is susceptible to the highly variable placement of Her. ischigualastensis (Gauthier, 1986;Novas, 1992Novas, , 1996Sereno & Novas, 1992;Fraser et al., 2002;Nesbitt et al., 2009a;Nesbitt, 2011;Nesbitt & Ezcurra, 2015;Cabreira et al., 2016;Langer et al., 2017;Baron et al., 2017a, b). Tied to the 'Herrerasaurus problem' are the positions of the early saurischians (which could be theropods) Chindesaurus bryansmalli, Tawa hallae and Eodromaeus murphi. ...
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Competing morphology-based phylogenetic analyses are routinely compared and evaluated only by a posteriori phylogenetic topology and group support, with little or no analysis of a priori data sources responsible for differing results. Although discordant characters and character-state scores are usually key to differing results (more so than variation in terminal taxa), programs currently do not exist to facilitate even simple two-way comparisons of morphology-based datasets, despite the impracticality and imprecision of manual assessment for datasets involving hundreds of characters. This paper, a first step to remedy this circumstance, presents methods (within TNT) to identify, compile and evaluate differences in characters and character states between datasets that yield different trees and degrees of group support. These apparently simple and urgently needed computer-assisted routines involve conceptual and computational challenges, even when competing morphology-based datasets are grossly similar. Example two-way comparisons are presented using pairs of similar morphology-based datasets for hominin and basal dinosaur radiations.
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Lewisuchus admixtus is an early dinosauriform described by Alfred Romer in 1972 on the basis of a single, incomplete skeleton, collected in lower Upper Triassic rocks of the renowned Chañares Formation, at the Los Chañares type‐locality, La Rioja Province, north‐western Argentina. Recent field explorations to the type‐locality resulted in the discovery of two partial articulated skeletons, which provide significant novel information. The cranial bones, presacral series, femur, tibia, and proximal tarsals of the new specimens match the preserved overlapping anatomy of the holotype and previously referred specimens of Lewisuchus admixtus, including the presence of unique combination of character states among dinosauriforms (anterior presacral column with additional ossification on the top of neural spines, dorsal neural spines fan‐shaped, anterior surface of the astragalus with a dorsally curved groove, and an inflated area on the anterior portion of the medial surface of this bone). This new information improves our understanding of the anatomy and taxonomy of early dinosauriforms and reinforces the role of Argentinean beds on the study of the origin of dinosaurs. This article is protected by copyright. All rights reserved.
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Triassic beds from Argentina and Brazil provide the most relevant fossil record of early dinosauriforms in terms of numerical abundance and taxonomic diversity. This record currently represents the best source to understand the origin and early evolutionary radiation of dinosaurs. In the present paper we offer an updated review focused on the available evidence of Carnian dinosaurs from this continent, but we also discuss the record of Triassic dinosaur precursors and the evolution of Triassic dinosaurs in other continents. It is clear that, aside the agreed taxonomic composition of some particular dinosaurian subclades (e.g., Herrerasauridae, Neotheropoda), there is no consensus about early dinosaur phylogeny, and our paper is not the exception. Recent years witnessed the discovery of several new early dinosaurian taxa, as well as reviews of the taxonomic allocation of several renowned forms such as Lagerpeton, Lewisuchus, Pisanosaurus, and Eoraptor. New analyses demonstrate that evidence supporting the taxonomic referrals of pre-Norian dinosaurs to Theropoda, Sauropodomorpha and Ornithischia are tenuous, at best. Here we present new anatomical observations and comparisons for each of these South American early dinosauriforms with the aim to test previous phylogenetic interpretations. Evidence from South America allows reviewing the phylogenetic relationships of taxa from other continents, including Tawa, Chindesaurus, and Daemonosaurus, which are here suggested to nest within Herrerasauria. Evidence at hand indicates that herrerasaurs were a successful clade of archaic predatory saurischians that inhabited both South and North America, and probably also India and Europe.
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The strata of the American Southwest, particularly the Chinle Formation and the Dockum Group, are critical to our understanding of faunal diversity and evolution in the Late Triassic. In recent decades, these strata have informed the evolution of close dinosaur relatives, which remain poorly sampled and enigmatic in their geographic distribution. Here, we describe and discuss a new non-dinosaurian dinosauromorph assemblage from the Los Esteros Member of the Santa Rosa Formation at the base of the Dockum Group in east-central New Mexico. This assemblage includes hindlimb fragments assignable to Silesauridae and Lagerpetidae. Much of the lagerpetid material, assignable to Dromomeron, is of unusually large size. Based on a dataset of complete lagerpetid femora, we estimate a total femoral length of 221.9 mm for one partial femur, making it the largest reported individual. We also provide biochronological support that at least a portion of the Los Esteros Member corresponds to the Otischalkian land vertebrate faunachron through the identification of non-Mystriosuchinae phytosaurs. Subsequently, we question the presence of a bifurcated lateral ridge on the squamosal of all phytosaurs currently assigned to Parasuchus. This is the first Otischalkian fauna identified from New Mexico, and it reveals lagerpetids achieved large body size earlier than previously recognized. Our identifications expand the geographic and temporal range of non-dinosaurian dinosauromorphs in the American Southwest. The material presented here, in conjunction with an increasing number of Dromomeron specimens, demonstrates that non-dinosauriform dinosauromorphs could match or exceed the body size of many coeval dinosaurs.
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