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Early ontogenetic changes in Mussaurus

Pol, D. & Powell, J.E. (2007) 'Skull anatomy of Mussaurus patagonicus (Dinosauria: Sauropodomorpha) from the Late Triassic of Patagonia', Historical Biology, 19:1, 125 - 144

Abstract: The skull anatomy of Mussaurus patagonicus from the Upper Triassic Laguna Colorada Formation is described based on a revision of the type material and several recently found specimens. The studied material include two distinct size classes of individuals. The type material consists of extremely young individuals whereas the new specimens are interpreted as juvenile or subadult individuals. The latter are significantly larger, having a skull approximately three times longer than the type material.

The skull anatomy of this taxon shows derived characters shared with some basal sauropodomorphs and eusauropods, which are absent in other basal sauropodomorphs (e.g. Thecodontosaurus, Plateosaurus). These include the presence of an extension of the infratemporal fenestra ventral to the orbit, dorsal and anterior rami of quadratojugal subperpendicular to each other, dorsoventral expansion of dentary at mandibular symphysis, slightly procumbent teeth with broad serrations restricted to the apical region (absent in some teeth).

Differences among the studied specimens helps to understand the early ontogenetic changes occurring in this basal sauropodomorph, revealing major changes in the rostral and temporal regions.


New anatomical information of Eoraptor and Herrerasaurus

Sereno, P.C. (2007) The phylogenetic relationships of early dinosaurs: a comparative report. Historical Biology, 2007; 19(1): 145–155

Abstract: Surprising new anatomical information has come to light for the early dinosaurs Eoraptor lunensis and Herrerasaurus ischigualastensis. Eoraptor has a mid mandibular jaw joint, and Herrerasaurus has a promaxillary fenestra at the anterior end of the antorbital fossa. Initial cladistic interpretation placed Herrerasaurus outside Dinosauria.

Since then, Eoraptor and Herrerasaurus have been placed at the base of Saurischia or within Theropoda in two large-scale quantitative analyses. A comparative approach is taken here to show, first, that character choice is a major factor behind differing results; only half of the character data critical for each interpretation is incorporated into the opposing analysis.

In that shared portion of data, furthermore, nearly 40 percent of character state scores vary for identical, or comparable, ingroup taxa. Resolving these conflictive interpretations is clearly where future progress will be made in understanding early dinosaur phylogenesis.

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Bon ces deux làa vont m'interesser lol