Chindesaurus

Chindesaurus (/ˌtʃɪndɪˈsɔːrəs/ CHIN-di-SAWR-əs) is a genus of herrerasaurid dinosaur that lived approximately 235-210 million years ago during the latter part of the Triassic Period in what is now the Southwestern United States. Chindesaurus was a small, bipedal carnivore that could grow up to 2 to 2.3 m (6.6 to 7.5 ft) long.

Chindesaurus
Temporal range: Late Triassic, 235–210 Ma
Restoration
Life restoration
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Family: Herrerasauridae
Genus: Chindesaurus
Long & Murry, 1995
Species:
C. bryansmalli
Binomial name
Chindesaurus bryansmalli
Long & Murry, 1995
Synonyms

Etymology

The genus name Chindesaurus is derived from the Navajo word chindi meaning "ghost" or "evil spirit" and the Greek word "sauros" (σαυρος) meaning "lizard";[1] thus, "ghost lizard" or "Lizard from Chinde Point". The specific name, bryansmalli, honors the discoverer, Bryan Small. Chindesaurus was described and named by R.A. Long and P.A. Murry in 1995; the type species is Chindesaurus bryansmalli. When this specimen was first discovered it was nicknamed "Gertie" after Gertie the Dinosaur and received much publicity.[2]

Description

Chindesaurus scale
Comparison of the size of Chindesaurus and a human

Chindesaurus is known from six incomplete specimens (seven if Caseosaurus is included). Of these, the type specimen PEFO 10395 is the most complete, consisting of a single tooth, a fragmentary neck vertebra, fragmentary back vertebrae, several rib fragments, two complete vertebrae from the hips, fragmentary tail vertebrae, a chevron, several fragmentary hip bones, a complete left femur and a fragmentary right femur, a fragmentary right tibia, and a right ankle bone.[2] The other specimens are more incomplete, consisting of isolated hip bones, upper leg bones (femora), and more vertebrae. The type and paratype specimens were approximately 2 to 2.3 metres (6.6 to 7.5 ft) in length.[3] Some estimates suggest that Chindesaurus weighed 50 kilograms (110.2 pounds) at most.[4]

Classification

Chindesaurus has been difficult to classify, and has been recovered in several different positions at the base of the saurischian family tree. When it was first discovered in 1984, the fossil specimen which would eventually be named Chindesaurus was thought to be a prosauropod.[5] When it was finally described and named a decade after its discovery by Long and Murry, they regarded it as a herrerasaurid, an opinion that has been followed by most paleontologists since.[2] Most phylogenetic analyses published through 2007 continued to find it to fall among the herrerasaurids,[6][7] though a few studies cast doubt on this, including one in 2007 by Irmis, Nesbitt and colleagues which found Chindesaurus to be a probable basal saurischian dinosaur, and noted that it shares a wide range of characteristics with several lineages of basal saurischians, making any classification problematic.[8] Rauhut (2003) noted that the medially expanded brevis shelf of Chindesaurus resembles that of crurotarsans, and not that of most dinosaurs, which is usually laterally expanded.[9] Benson and Brussatte (2012) found that Chindesaurus was a basal saurischian related to Herrerasaurus.[3]

One specimen originally assigned to Chindesaurus, from the Tecovas Formation of Texas, was later placed in its own genus and species, Caseosaurus crosbyensis.[10] Subsequent research has shown that this separation was probably in error, and that the two forms represent the same species.[11] Nesbitt, Irmis and Parker agreed in a 2007 paper that there is little reason to separate Caseosaurus from Chindesaurus, and the two even share some unique characteristics not found in similar species. Nesbitt and colleagues suggested that any differences between the two were probably related to differences in size. However, since both species are so fragmentary, they decided not to formally make them synonyms.[12]

The following is a cladogram based on the phylogenetic analysis by Hans-Dieter Sues, Sterling J. Nesbitt, David S Berman and Amy C. Henrici, in 2011, which indicated that Chindesaurus is a herrerasaurid.[13] A similar position for Chindesaurus was recovered by the analyses by Baron, Norman & Barrett and Baron & Williams.[14][15]

  Dinosauria  

Ornithischia

 Saurischia 

Sauropodomorpha

 Theropoda 
 Herrerasauridae 

Staurikosaurus

Herrerasaurus

Chindesaurus

Eoraptor

Daemonosaurus

Tawa

Neotheropoda

Distinguishing anatomical features

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. (2007), Chindesaurus can be distinguished based on the following characteristics:

  • a triangular rugosity is present on the postacetabular process
  • the proximal tibial intercondylar groove is strongly situated medially
  • the posterior edge of the fibular condyle of the proximal tibia is straight when examined in proximal view
  • the presence of a ventral cleft on the astragalus

Paleoecology

Provenance and occurrence

The holotype specimen of Chindesaurus PEFO 10395 is a partial skeleton, discovered in the Petrified Forest National Park member of the Chinle Formation in Apache County, Arizona. Its remains were discovered by Bryan Small in 1984, in blue mudstone which was deposited during the Norian stage of the Triassic, approximately 228-208 million years ago.[16][17] Specimen PEFO 4849, which consists only of a dorsal vertebra was referred to the genus. It was collected in Norian-aged sediments in a different part of the Upper Petrified Forest member. Specimen PEFO 33982, which consists of nine vertebrae, an ilium fragment, a proximal femur, and other bone fragments was also collected in Norian-aged sediments of Upper Petrified Forest member. These two specimens are housed in the collection of the University of California Museum of Paleontology in Berkeley, California.

In the Bull Canyon Formation, in New Mexico, specimens NMMNH P16656 and NMMNH P17325 were discovered in sediments deposited during the Norian and Lancian stages of the Late Triassic, respectively. The assignment of these two specimens to Chindesaurus has now come under question.[18] These specimens are housed in the collection of the New Mexico Museum of Natural History and Science in Albuquerque, New Mexico.

Additional material referable to Chindesaurus was discovered in 2006, in gray/green siltstone at the Hayden Quarry of the Petrified Forest Member of the Chinle Formation in New Mexico. Another specimen, TMM 31100-523 which consists of a proximal femur, was discovered in the Colorado City Formation in Texas, in mudstone considered to be from the Carnian stage of the Triassic, approximately 235-228 million years ago. It is currently housed in the collection of the Texas Memorial Museum in Austin, Texas.

Fauna and habitat

The Upper Petrified Forest National Park member of the Chinle Formation was an ancient floodplain where phytosaurs, rauisuchids, archosaurs, pseudosuchians, and other tetrapods lived and competed with the dinosaur Chindesaurus and its relative Coelophysis for resources. This paleoenvironment also had abundant lungfish and clams.

References

  1. ^ Liddell, Henry George & Robert Scott (1980). A Greek-English Lexicon (Abridged Edition). United Kingdom: Oxford University Press. ISBN 978-0-19-910207-5.
  2. ^ a b c Long and Murry, (1995). "Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States." New Mexico Museum Natural History Science Bulletin, 4: 1-254.
  3. ^ a b Benson, R.B.J. & Brussatte, S. (2012). Prehistoric Life. London: Dorling Kindersley. p. 217. ISBN 978-0-7566-9910-9.
  4. ^ "Chindesaurus". Hostgator.com. Retrieved 31 May 2013.
  5. ^ Meyer, (1986). "D-Day on the Painted Desert." Arizona Highways, 62(7): 3-13.
  6. ^ Bittencourt and Kellner, (2004). "The phylogenetic position of Staurikosaurus pricei Colbert, 1970 from the Triassic of Brazil." Journal of Vertebrate Paleontology, 24(3):.
  7. ^ Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs, (2007). "A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs." Science, 317: 358-361.
  8. ^ Irmis, R.B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D.T., and Downs, A. (2007). "A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs". Science 317: 358-361
  9. ^ Rauhut, 2003. The interrelationship and evolution of basal theropod dinosaurs. Special Papers in Palaeontology. 69, 1-215.
  10. ^ Hunt, Lucas, Heckert, Sullivan and Lockley, (1998). "Late Triassic Dinosaurs from the Western United States." Geobios, 31(4): 511-531.
  11. ^ Langer, (2004). "Basal Saurischia." In Weishampel, Dodson and Osmolska (eds.). The Dinosauria Second Edition. University of California Press. 861 pp.
  12. ^ Nesbitt, Irmis and Parker, (2007). "A critical re-evaluation of the Late Triassic dinosaur taxa of North America." Journal of Systematic Palaeontology, 5(2): 209–243.
  13. ^ Hans-Dieter Sues; Sterling J. Nesbitt; David S Berman; Amy C. Henrici (2011). "A late-surviving basal theropod dinosaur from the latest Triassic of North America". Proceedings of the Royal Society B. 278 (1723): 3459–64. doi:10.1098/rspb.2011.0410. PMC 3177637. PMID 21490016.
  14. ^ Baron, M.G., Norman, D.B., and Barrett, P.M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543: 501–506. doi:10.1038/nature21700
  15. ^ Matthew G. Baron; Megan E. Williams (2018). "A re-evaluation of the enigmatic dinosauriform Caseosaurus crosbyensis from the Late Triassic of Texas, USA and its implications for early dinosaur evolution". Acta Palaeontologica Polonica. in press. doi:10.4202/app.00372.2017.
  16. ^ Parker, W. G., R. B. Irmis, and S. J. Nesbitt. 2006. Review of the Late Triassic dinosaur record from Petrified Forest National Park . Pages 160-161 in Parker, W. G., S. R. Ash, and R. B. Irmis, editors. A century of research at Petrified Forest National Park: geology and paleontology. Museum of Northern Arizona, Flagstaff, Arizona. Bulletin 62.
  17. ^ Litwin, R.J., Traverse, A., and Ash, S.R., 1991. Preliminary palynological zonation of the Chinle Formation, southwestern U.S.A., and its correlation to the Newark Supergroup (eastern U.S.A.). Review of Paleobotany and Palynology, v. 77, p. 269-287.
  18. ^ Nesbitt, Irmis and Parker, 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology. 5(2), 209–243.
Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Avetheropoda

Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.

Buriolestes

Buriolestes (meaning "Buriol's robber") is a genus of early sauropodomorph dinosaurs from the Late Triassic Santa Maria Formation of the Paraná Basin in southeastern Brazil. It contains one species, B. schultzi, named in 2016. The type specimen was found alongside a specimen of the lagerpetid dinosauromorph Ixalerpeton.

Carnian

The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic series (or earliest age of the Late Triassic epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event (known as the Carnian Pluvial Event) occurred during the Carnian and seems to be associated with important extinctions or biotic radiations.

Caseosaurus

Caseosaurus ( KAY-zee-o-SAWR-əs) is a dubious genus of herrerasaurid theropod dinosaur that lived approximately 235 to 228 million years ago during the latter part of the Triassic Period in what is now Texas, in North America. Caseosaurus was a small, lightly-built, bipedal, ground-dwelling carnivore, that could grow up to 2 m (6.6 ft) long.

Cerapoda

Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.

Daemonosaurus

Daemonosaurus (pron.:"DAY-mow-no-SORE-us") is an extinct genus of theropod dinosaur from the Late Triassic of New Mexico. Fossils have been found from deposits in the Chinle Formation, which is latest Triassic in age. While theropods had diversified into several specialized groups by this time, Daemonosaurus is a basal theropod that lies outside the clade Neotheropoda. Daemonosaurus is unusual among early theropods in that it had a short skull and long protruding teeth.

Dinosauriformes

Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.

Dromomeron

Dromomeron (meaning "running femur") is a genus of lagerpetonid dinosauromorph archosaur that lived around 220 to 211.9 ± 0.7 million years ago. The genus contains species known from Late Triassic-age rocks of the southwestern United States and northwestern Argentina. It is described as most closely related to the earlier Lagerpeton of Argentina, but was found among remains of true dinosaurs like Chindesaurus, indicating that the first dinosaurs did not immediately replace related groups.Based on the study of the overlapping material of Dromomeron and Tawa hallae, Christopher Bennett proposed that the two taxa were conspecific, forming a single growth series of Dromomeron. However, noting prominent differences between their femurs which cannot be attributed to variation with age, Rodrigo Muller 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.

Haya griva

Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.

Herrerasauridae

Herrerasauridae is a family of carnivorous basal saurischian dinosaurs. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago (Late Triassic), before becoming extinct by the end of the Triassic period. Herrerasaurids were relatively small-sized dinosaurs, normally not more than 4 metres (13 ft) long. The best known representatives of this group are from South America (Brazil, Argentina), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete herrerasaurids have been found in North America, and they may have inhabited other continents as well.

Herrerasaurid anatomy is unusual and specialized, and they are not considered to be ancestral to any later dinosaur group. They only superficially resemble theropods and often present a mixture of very primitive and derived traits. The acetabulum is only partly open, and there are only two sacral vertebrae, the lowest number among dinosaurs. The pubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficially tetanuran-like terminal expansion, especially prominent in H. ischigulastensis. The hand is primitive in having five metacarpals and the third finger longer than the second, but resembles those of theropods in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible, which is also found in theropods.

Jeholosauridae

Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.

Jingshanosaurus

Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.

Neotheropoda

Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.

Orionides

Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.

Orodrominae

Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.

Staurikosaurus

Staurikosaurus (Pronounced "STORE-ee-koh-SAWR-us", "Southern Cross lizard") is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.

Xixiposaurus

Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.

Zupaysaurus

Zupaysaurus (; "ZOO-pay-SAWR-us") is a genus of early theropod dinosaur living during the Norian stage of the Late Triassic in what is now Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. Although a full skeleton has not yet been discovered, Zupaysaurus can be considered a bipedal predator, up to 4 metres (13 ft) long. It may have had two parallel crests running the length of its snout.

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