Wednesday, November 17, 2010

The two undescribed Ischigualasto basal saurischians/theropods

There are two undescribed potential basal theropods from the Ischigualasto Formation, both currently described largely in abstracts. 

undescribed possible theropod (Sereno, 2007)
Norian, Late Triassic
Valle de la Luna Member of the Ischigualasto Formation, San Juan, Argentina
- (~1.6 m) incomplete skeleton including maxilla, cervical vertebrae, distal caudal vertebrae, carpus, manus, pubis, femur and tibia
partial skeletons
Comments- This taxon has only been described in an abstract by Martinez et al. (2008) so far, though the official description is under review. Sereno (2007) states this is a closely related taxon to Eoraptor lunensis, while Martinez et al. (2008) place it as a basal theropod presumably closer to avepods than Eoraptor and herrerasaurids based on several mentioned characters. Phylogenetically informative characters include- promaxillary fenestra; cervical pleurocoels; distal caudal prezygapophyses ~15% of centrum length; pentadactyl manus; extensor pits on metacarpals; pubis distally tapered; pubis posteriorly curved; anterior fossa above distal condyles on femur; tibia longer than femur. Noted additional differences from Eoraptor include more gracile elements, and slender anterior maxillary teeth which are more than twice as long as the former genus.
References- Sereno, 2007. The phylogenetic relationships of early dinosaurs: A comparative report. Historical Biology. 19(1), 145-155.
Martinez, Sereno and Alcober, 2008. A new basal theropod from the Ischigualasto Formation of San Juan Province, Argentina. in Calvo, Valieri, Porfiri and dos Santos (eds.). Libro de Resumenes, III Congreso Latinoamericano de Paleontologia de Vertebrados. Universidad Nacional del Comahue, Neuquen, Argentina. 153.

undescribed herrerasaurid (Ezcurra and Novas, 2007)
Late Carnian-Early Norian, Late Triassic
Cancha de Bochas Member of the Ischigualasto Formation, San Juan, Argentina
- (MACN-PV 18.649a) (small) vertebrae, distal ulna, carpus, manus, pedal phalanges
Diagnosis- (after Ezcurra and Novas, 2007) manual unguals with a posteriorly bifurcated lateral groove.
(after Ezcurra, 2010) manual phalanx II-1 with conspicuous longitudinal ridge on its proximolateral border.
Comments- This specimen was discovered in the 1960s, but not noted until an abstract by Ezcurra and Novas (2007). That paper and Ezcurra (2010) placed it in Herrerasauridae, the latter using a version of Yates' sauropodomorph analysis. It was a herrerasaur based on- manual phalanx I-1 longer than metacarpal I; strongly curved manual unguals; metacarpals IV-V ventral to the others. While these are shared with Herrerasaurus, the unknown forelimb of Staurikosaurus makes the relationship between these three taxa uncertain. The new taxon will be described in more detail by Ezcurra and Novas (in prep.).
References- Ezcurra and Novas, 2007. New dinosaur remains (Saurischia: Herrerasauridae) from the Ischigualasto Formation (Carnian) of NW Argentina. Ameghiniana. 44, 17R.
Ezcurra and Novas, 2008. A review of the dinosaur diversity of the Ischigualasto Formation (Carnian, NW Argentina): Insights on early dinosaur evolution. in Langer, Bittencourt and Castro (eds.). Boletim de Resumos, VI Simposio Brasileiro de Paleontologia de Vertebrados, Paleontologia, Edicao especial. Universidad de Sao Pablo: Ribeirao Preto. 88-89.
Ezcurra, 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: A reassessment of dinosaur origin and phylogeny. Journal of Systematic Palaeontology. 8(3), 371-425.
Ezcurra and Novas, in prep.

I can send a copy of any of the references if emailed at .

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