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Tawa
Fossil range: Late Triassic, 215 Ma
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Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Genus: Tawa
Nesbitt et al., 2009
Species
  • T. hallae Nesbitt et al., 2009 (type)

Tawa (named after the Hopi word for the Puebloan sun god) is a genus of theropod dinosaur from the Late Triassic period. It is estimated to have been 2 m (6.5 ft) long. In 2004, a partial skeleton was excavated, and in 2006 two nearly complete fossil skeletons of Tawa and parts of six others were found close together in the Hayden Quarry at Ghost Ranch in New Mexico (part of the Petrified Forest Member of the Chinle Formation) in strata dating to approximately 215-213 million years ago.[1] The discovery is significant and suggests that the earliest dinosaurs arose in the ancient area of Gondwana that is now South America and spread from there.[2] The type species is T. hallae, described in 2009 by Nesbitt et al. The specific name honours Ruth Hall, founder of the Ghost Ranch Museum of Paleontology.[3]

Contents

Discovery

Fossils now attributed to Tawa were first discovered in 2004. The holotype, cataloged GR 241, is a mostly complete skull and postcranial skeleton belonging to a juvenile individual. Fossils of at least seven other individuals were also discovered at the site. One of these specimens, cataloged GR 242, is also nearly complete. An isolated femur suggests that adults were at least 30% larger than the holotype. All of these specimens are from the Hayden Quarry and date to between 215 to 213 million years old. Tawa was formally described in 2009 by a group of six American researchers led by Sterling J. Nesbitt of the American Museum of Natural History.[3] At the time of publication in the journal Science, Nesbitt was a postdoctoral researcher at the University of Texas at Austin's Jackson School of Geosciences.[4]

Classification

 Dinosauria 

 Ornithischia 


 Saurischia 

Sauropodomorpha 


 Theropoda 

Herrerasauridae 


    

 Eoraptor 


    

Tawa


 Neotheropoda 
    

 Coelophysis 



 "Syntarsus" kayentakatae 



    

 Liliensternus 



 To Jurassic Theropods 









The 2009 description of Tawa places this genus as more basal than Coelophysis, an early theropod from the Late Triassic and Early Jurassic. Tawa is, however, more advanced than the earliest known dinosaurs, Eoraptor, Herrerasaurus,[5] and Staurikosaurus. A cladistic analysis of Tawa and other early theropods indicate that the Coelophysoidea, a group of early dinosaurs, may be an artificial grouping because Tawa combines classic coelophysoid features with features which appear to be ancestral to the neotheropods. Tawa is believed to be the sister taxon of Neotheropoda,[3] a group of carnivorous dinosaurs which bore only three functional digits on their feet.

See also

References

  1. ^ Maffly, Brian (December 10, 2009), "New Mexico find sheds light on early dinosaur dispersal", Salt Lake Tribune, http://www.sltrib.com/News/ci_13969087  
  2. ^ "New T. Rex Cousin Suggests Dinosaurs Arose in S. America", National Geographic, December 10, 2009, http://news.nationalgeographic.com/news/2009/12/photogalleries/091210-new-dinosaur-evolution-pictures-south-america/  
  3. ^ a b c Nesbitt, S. J.; Smith, N. D.; Irmis, R. B.; Turner, A. H.; Downs, A. & Norell, M. A. (2009), "A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs", Science 326 (5959): 1530–1533, doi:10.1126/science.1180350  .
  4. ^ Airhart, Marc (December 10, 2009), "New Meat-Eating Dinosaur Alters Evolutionary Tree", Jackson School of Geosciences, http://www.jsg.utexas.edu/news/rels/121009.html  
  5. ^ Harmon, Katherine (December 10, 2009), "Newly Discovered T. Rex Relative Fleshes Out Early Dino Evolution", Scientific American, http://www.scientificamerican.com/article.cfm?id=t-rex-relative-tawa  

External links

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