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Re: Herrerasaurus - what was it?



 Analogous problems exist for Guaibasaurus (basal theropod, basal
 saurischian, or basal saur... Well, let's just say a new strong
 alternative has come up)

No, let's spell it out. SVP meeting abstracts are embargoed till the time of their presentation, but no further. Here goes:

Martin Ezcurra & Fernando Novas (2009): Guaibasauridae, a new clade of Triassic basal sauropodomorphs, Journal of Vertebrate Paleontology, online-only supplement to 29(3), 92A

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The family Guaibasauridae was coined as a monospecific entity composed by *Guaibasaurus candelariensis* from the Norian Caturrita Formation of Brazil. Since then, the phylogenetic position of *Guaibasaurus* remained controversial, being alternatively interpreted as a basal saurischian or a basal theropod. Nevertheless, a new cladistic analysis depicts Guaibasaurus as closely related with *Panphagia*, *Agnosphitys*, *Saturnalia*, and two yet undescribed forms from Argentina and India. We employ the term Guaibasauridae for the monophyletic clade gathering these Late Triassic taxa, which lies at the base of Sauropodomorpha. In particular, *Guaibasaurus* is for the first time included within Sauropodomorpha, supported by the presence of proximal caudal vertebrae with the base of the neural spine anteroposteriorly longer than half the length of the neural arch, ilium with strongly laterally curved blade and elongated pubic peduncle, and ischial shaft triangular-shaped in cross-section. Features supporting the monophyly of Guaibasauridae include: ilium with incipiently open acetabulum, elongated postacetabular process, femur with proximal anterior trochanter at level with femoral head, and tibial distal end with concave posterolateral corner. Contrarily to recent interpretations, *Panphagia* is not depicted as the most basal sauropodomorph, and characters supporting its original assignment are more widely distributed among basal saurischians (distally curved anterior dentary teeth and sub-circular distal ischium) or missinterpreted [sic] (symmetric proximal tibial condyles). Accordingly, Guaibasauridae is interpreted as a large monophyletic [duh] clade of early dinosaurs, which radiated during late Carnian-Norian times and attained a wide geographic distribution. Furthermore, no large monophyletic clades were previously recognized among basal dinosaurs, and Guaibasauridae constitutes the first evidence of a large clade which radiated apart from the branch leading towards
Jurassic and Cretaceous taxa, in this case the sauropod lineage.

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The presentations themselves are secret without explicit permission by the authors, but in this case the abstract pretty much says it all, so you're not missing much.

The same holds for the following poster on the phylogenetic position of *Silesaurus*, which I remember as not particularly information-rich:

Grzegorz NiedÅwiedzki, RafaÅ Piechowski & Tomasz Sulej (2009): New data on the anatomy and phylogenetic position of *Silesaurus opolensis* from the late Carnian of Poland, Journal of Vertebrate Paleontology, online-only supplement to 29(3), 155A

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*Silesaurus opolensis* is one of the best-known early dinosauriform archosaurs, represented by several, partially articulated skeletons and hundreds of isolated bones collected from the Keuper beds (Late Triassic: late Carnian) at the KrasiejÃw [site?] near Opole, Upper Silesia, Poland. *Silesaurus* is peculiar in having herbivorous-like teeth as well as evidence for a beak on the anterior end of the dentary. The phylogeny of basal dinosaurs and closely related taxa has been examined by numerous cladistic analyses. However, areas of uncertainty remain, such as the relationships of *Silesaurus*-like dinosauriforms to basal ornithischian and sauropodomorph dinosaurs. Following the initial description of this taxon in 2003, *Silesaurus* has been the subject of detailed anatomical study. We present new observations on the anatomy of the skull, dentary, limbs and pelvis, shedding new light on the phylogenetic position of this taxon. A new phylogenetic dataset was constructed to resolve relationships amongst dinosauromorphs, *Silesaurus*-like dinosauriforms, basal saurischians (including basal sauropodomorphs) and basal ornithischians. This dataset includes 25 species and 125 characters (10 new); characters were compiled based upon a thorough reassessment of previous phylogenetic datasets and direct examination of relevant specimens. Character scorings were drawn from previous analyses as well as the recently published and ongoing results of taxonomic reviews of the Late Triassic dinosauriform and basal dinosaur record. Analysis of the new dataset suggests that *Silesaurus opolensis* is the basalmost known ornithischian, forming the sister taxon of other early ornithischians, including *Pisanosaurus*, *Lesothosaurus*, *Eocursor*, âfabrosauridsâ and Heterodontosauridae. The major ornithischian character of *Silesaurus* is a beak at the tip of mandible. The symphysis does not show permanent junction of dentaries and they clearly had significant mobility, although their tip was apparently armed with horny cover. *Silesaurus* was also advanced in the construction of
its pelvis and sacrum relative to other early dinosauromorphs.

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And while I am at it...

Sterling Nesbitt (2009): The antiquity of Archosauria and the origin of Late Triassic archosaur assemblages, Journal of Vertebrate Paleontology, online-only supplement to 29(3), 155A

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Archosaurs have a rich history that originated in the Triassic and continues today with two extant clades, the crocodylians and the avians. Nonetheless, the initial divergence of Archosauria is poorly understood. Few archosaur fossils have been found prior to the Ladinian Stage (late Middle Triassic), even though published archosaur phylogenies predict most Triassic archosaur ghost lineages stretch into the Middle Triassic or earlier. New discoveries of archosaurs from the Middle Triassic Manda Formation of Africa, the Moenkopi Formation of North America, and the re-identification of existing material from the Early Triassic of China help fill these ghost lineages. I conducted a thorough phylogenetic analysis (80 archosauriform taxa, 412 characters) to assess the early evolution of Archosauria. The analysis recovered a well resolved, robustly supported consensus tree that includes a monophyletic Archosauria. âRauisuchiansâ are found to be paraphyletic, but include a monophyletic poposauroid clade, rauisuchid clade, and crocodylomorph clade. A monophyletic clade containing Silesaurus and similar forms is supported as the sistertaxon to Dinosauria. Time-calibration of this phylogeny indicates that the origin and initial diversification of Archosauria occurred prior to the Middle Triassic, just after the Permian- Triassic extinction. A *Silesaurus*-like taxon from the Anisian Manda Formation indicates that the Pterosauria, Dinosauromorpha, Dinosauriformes, and Dinosauria lineages were present by the Anisian. Similarly, the âsail-backedâ poposauroid *Xilousuchus* from the late Early Triassic of China indicates that Archosauria, the Ornithodira, Phytosauria, Aetosauria, Ornithosuchidae, and Paracrocodylomorpha lineages were present by the end of the Early Triassic. High rates of homoplasy, long ghost lineages, and high rates of character evolution characterize the early history of Archosauria. These data imply that much of the early history of Archosauria has not been recovered, and the typical archosaur assemblages in the Late
Triassic were possibly established by the Middle Triassic.

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I should perhaps point out that the Anisian is the first of the two stages of the Middle Triassic. -- In case you're wondering, Paracrocodylomorpha is a misnamed clade that _includes_ Crocodylomorpha and its closest relatives (compare Paraves).