Tawa hallae
Tawa hallae | |
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Life restoration | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda (?) |
Genus: | †Tawa Nesbitt et al., 2009 |
Species: | †T. hallae
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Binomial name | |
†Tawa hallae Nesbitt et al., 2009
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Tawa (named after the
Description
Tawa was estimated to have been 2.5 m (8 ft 2 in) long as an adult, with a weight of 15 kg (33 lb).
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group. According to Nesbitt et al. (2009) Tawa can be distinguished based on the following features: the prootic bones meet on the ventral midline of the endocranial cavity, the anterior tympanic recess is greatly enlarged on the anterior surface of the basioccipital and extends onto the prootic and the parabasisphenoid, a deep recess is present on posterodorsal base of the paroccipital process, a sharp ridge extending dorsoventrally on the middle of the posterior face of the basal tuber, an incomplete ligamental
Discovery
Fossils now attributed to Tawa were first discovered in 2004. The
All of these specimens are from the Hayden Quarry, a site in New Mexico, which preserves many fossils of early dinosaurs and their close relatives. They were discovered in gray/green siltstone dating to the Norian stage of the Triassic period, about 215-213 million years ago.[5] 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.[6]
Based on the study of the overlapping material of Dromomeron romeri and Tawa, S. Christopher Bennett proposed that the two taxa were conspecific, forming a single growth series with D. romeri being the juvenile and Tawa being the adult.[7] However, noting prominent differences between their femora which cannot be attributed to variation with age, Rodrigo Müller rejected this proposal in 2017. He further noted that while D. romeri is known from juveniles only, it shares many traits in common with D. gigas, which is known from mature specimens.[5]
Classification
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The
.Sues et al. (2011) considered Tawa a
In 2011, Martinez and colleagues concluded that Tawa was the basalmost coelophysoid,
Cau (2018)[15] and Novas et al. (2021)[16] considered Tawa a non-herrerasaurid herrerasaur, although the first study placed Herrerasauria outside Dinosauria and the second placed it in Saurischia.
Paleoecology
The Hayden Quarry at Ghost Ranch belongs to the lower portion of the Petrified Forest Member of the Chinle Formation in New Mexico. The discovery of Tawa alongside the relatives of Coelophysis and Camposaurus supports the hypothesis that the earliest dinosaurs arose in Gondwana during the Late Triassic period in what is now South America, and radiated around the globe from there.
Ghost Ranch was located close to the equator 200 million years ago, and had a warm, monsoon-like climate with heavy seasonal precipitation. Hayden Quarry, an excavation site at Ghost Ranch, has yielded a diverse collection of fossil material that included the first evidence of dinosaurs and less-advanced dinosauromorphs from the same time period. The discovery indicates that the two groups lived together during the early Triassic period 235 million years ago.
Based on their review of the early carnivorous dinosaur fauna from Ghost Ranch and the Ischigualasto Formation Nesbit et al. (2009) observed that each was descended from a separate lineage, and inferred that the "South American" protocontinent Gondwana was the ancestral range for basal dinosaurs. Nesbit et al. (2009) went on to note that dinosaurs left their ancestral range in Gondwana and 200 million years ago they dispersed across the adjoined continents of Pangea.[3]
Nesbit et al. (2009) noted that repeated flooding events collected vertebrate bones, carcasses, and plant material from the landscape surface, possibly in hyperconcentrated flows, and deposited them at what is now Hayden Quarry. It was observed that these flooding events were separated by intervals where there was standing water and weakly developed, poorly drained (hydromorphic) soil formation. The Tawa specimens were very well preserved which suggests that they were buried extremely soon after dying.[3]
See also
References
- ^ Maffly, Brian (December 10, 2009), "New Mexico find sheds light on early dinosaur dispersal", Salt Lake Tribune, archived from the original on December 13, 2009
- ^ "New T. Rex Cousin Suggests Dinosaurs Arose in S. America", National Geographic, December 10, 2009, archived from the original on December 13, 2009
- ^ S2CID 8349110.
- ISBN 9780691167664.
- ^ PMID 28489198.
- ^ Airhart, Marc (December 10, 2009), "New Meat-Eating Dinosaur Alters Evolutionary Tree", Jackson School of Geosciences, archived from the original on March 10, 2010
- ^ Bennett, S.C. (2013). "A Rebuttal to Nesbitt's and Hone's "An external mandibular fenestra and other archosauriform characteristics in basal pterosaurs"" (PDF). International Symposium on Pterosaurs: 19–22.
- ^ DML: http://dml.cmnh.org/2009Dec/msg00122.html
- ^ Harmon, Katherine (December 10, 2009), "Newly Discovered T. Rex Relative Fleshes Out Early Dino Evolution", Scientific American
- PMID 21490016.
- S2CID 33506648.
- .
- PMID 25544219.
- S2CID 205254710.
- S2CID 44078918.
- .
- ^ Braginetz, Donna. "A new species of dinosauromorph (lower left) was among the mixed assemblage of dinosaurs and dinosauromorphs found at Hayden Quarry in Ghost Ranch, N.M." American Museum of Natural History. Retrieved 31 March 2013.
- ^ Irmis et al. 2007[full citation needed]