Tuesday, March 29, 2011

Eodromaeus thoughts

I just added Eodromaeus to the Database and noted a few things.

- PVSJ 563 was listed as a paratype, but this is a typo (Sereno, pers. comm.).

- Eodromaeus specimens were thought to be Eoraptor until 2000, but Sereno (pers. comm.) confirms there are indeed several specimens besides the holotype correctly referred to Eoraptor that await description.

- Several of Eodromaeus' listed autapomorphies are shared with Herrerasaurus, such as the ventrally convex maxillary alveolar margin (more poorly developed in Sanjuansaurus), large distal carpal 5 overlapping distal carpal 4 with a posteroventral heel (note Sereno misidentified carpal 5 as 4 in 1993- Ezcurra, 2010), and pubic apron with sinuous lateral margin (in Sanjuansaurus too, but not developed much in Staurikosaurus).  Of course Eodromaeus specimens are adult so it's not a synonym, but these might be saurischian/theropod plesiomorphies.

- The supposed small herrerasaurid forelimb MACN-PV 18.649a mentioned by Ezcurra and Novas (2007, 2008) may be referrable to Eodromaeus.  It was referred to Herrerasauridae due to- enlarged distal carpal V; manual phalanx I-1 longer than metacarpal I; strongly curved manual unguals; metacarpals IV-V ventral to the others.  All of these are present in Eodromaeus as well.  Ezcurra (2010) states that it differs from Herrerasaurus in having manual phalanx II-1 with a conspicuous longitudinal ridge on its proximolateral border.  Eodromaeus does have a marked proximolateral projection on II-1, but whether this is a ridge or not is not described.  Ezcurra's (2010) matrix could be checked for further information on the forelimb's morphology, which could then be compared to Eodromaeus.

- In Martinez et al.'s (2011) cladogram, Tawa is the basalmost coelophysoid.  In this case, Avepoda contains Tawa and other coelophysoids under ACCTRAN character optimization, but excludes Coelophysoidea under DELTRAN optimization.  Gotta love apomorphy-based definitions...

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.

Martinez, Sereno, Alcober, Columbi, Renne, Montanez and Currie, 2011. A basal dinosaur from the dawn of the dinosaur era in Southwestern Pangaea. Science. 331, 206-210.

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