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Coelophysis? kayentakatae

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Coelophysis? kayentakatae
Temporal range: Early Jurassic
↓
Holotype skull MNA V2623
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Neotheropoda
Genus: †Coelophysis (?)
Species:
†C.? kayentakatae
Binomial name
†Coelophysis? kayentakatae
(Rowe, 1989)
Synonyms[1][2]
  • Syntarsus kayentakatae Rowe, 1989 (preoccupied)
  • Coelophysis kayentakatae (Rowe, 1989) Bristowe and Rowe, 2004
  • Megapnosaurus kayentakatae (Rowe, 1989) Ivie et al., 2001

Coelophysis? kayentakatae is an extinct species of neotheropod dinosaur that lived approximately 200–196 million years ago during the early part of the Jurassic Period in what is now the southwestern United States.[3] It was originally named Syntarsus kayentakatae, but the genus Syntarsus was found to be preoccupied by a Colydiine beetle, so it was moved to the genus Megapnosaurus,[4] and then to Coelophysis. A recent reassessment suggests that this species may require a new genus name.[5]

Discovery

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The holotype of "S." kayentakatae (MNA V2623) was recovered in the Silty Facies Member of the Kayenta Formation in Arizona. This material was collected in 1977 from carbonaceous sandstone deposited during the Sinemurian and Pliensbachian stages of the Jurassic period.[6] Specimen UCMP V128659 was discovered in 1982 and referred to Megapnosaurus kayentakatae by Rowe (1989),[7] as a subadult gracile individual and later, Tykoski (2005)[8] agreed. Gay (2010) described the specimen as the new tetanurine taxon Kayentavenator elysiae,[9] but Mortimer (2010) pointed out that there was no published evidence that Kayentavenator is the same taxon as S. kayentakatae.[10]

The species epithet of "S." kayentakatae refers to Dr. Kathleen Smith, nicknamed "Kayenta Kay" for her extensive work in the Kayenta Formation, which included the discovery of the type specimen of this species.[11]

Description

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Restoration of C.? kayentakatae feeding on a Scutellosaurus

S. kayentakatae was a relatively small dinosaur, reaching 2.5 m (8.2 ft) in length and 30 kg (66 lb) in body mass.[12] It had two small, parallel crests which may demonstrate an evolutionary step toward later and larger neotheropods, such as the more advanced and larger Dilophosaurus. Both possess a "weak joint" between the premaxillary and the maxillary bones, creating a hooked premaxillary jaw.

Specimen UCMP V128659 was discovered in 1982 and referred to Syntarsus kayentakatae by Rowe in 1989[11] as a subadult gracile individual and Tykoski (2005)[13] later agreed. Gay (2010) classified the specimen as tetanurine Kayentavenator elysiae.[14] Mortimer (2010) pointed out that there was no published evidence to support Kayentavenator being the same as Syntarsus kayentakatae except for in Ezcurra (2012) based on an unpublished analysis.[10]

According to Tykoski and Rowe (2004)[15][16] Syntarsus kayentakatae can be distinguished based on the following characteristics:

  • the presence of nasal crests on the skull
  • the frontal bones on the skull are separated by a midline anterior extension of the parietal bones

Furthermore, they list a transverse groove on the anterior astragalar surface, as an additional autapomorphy, however, it's also present in Coelophysis bauri and the Shake-n-Bake coelophysid (Tykoski, 2005). [17]

Classification

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It was originally included in the genus Syntarsus along with type species Syntarsus rhodesiensis, but the name is preoccupied by a junior synonym of beetle genus Cerchanotus. The dinosaur genus was renamed Megapnosaurus in 2001.[4] Both species have sometimes been reclassified as Coelophysis species.[1]

Marsh and Rowe (2020) retain the generic name Syntarsus for both QG 1 and MNA V2623, and the respective specimens assigned to these taxa, as opposed to Coelophysis or Megapnosaurus, due to systematic relationships within Coelophysoidea in flux. As such, congenericity or the need for Megapnosaurus would not be supported if Coelophysis bauri, Megapnosaurus rhodesiensis, and "Syntarsus" kayentakatae do not form respective clades, as evidenced by their phylogenetic analyses. [18]

Ezcurra et al. (2021) found that "Syntarsus" kayentakatae was not closely related to Coelophysis bauri or to Megapnosaurus rhodesiensis.[19]

Paleoecology

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The Kayenta Formation is part of the Glen Canyon Group that includes formations not only in northern Arizona but also parts of southeastern Utah, western Colorado, and northwestern New Mexico. The formation was primarily deposited by rivers, with the silty facies created by the slower, more sluggish part of the river system. A definitive radiometric dating of this formation has not yet been made, and the available stratigraphic correlation has been based on a combination of radiometric dates from vertebrate fossils, magnetostratigraphy and pollen evidence.[20]

Snout and front teeth of C. bauri and C.? kayentakatae

During the Early Jurassic period, the land that is now the Kayenta Formation experienced rainy summers and dry winters. By the Middle Jurassic period it was being encroached upon from the north by a sandy dune field that would become the Navajo Sandstone.[21] The animals here were adapted to a seasonal climate and abundant water could be found in streams, ponds and lakes. Syntarsus kayentakatae shared its paleoenvironment with other dinosaurs, such as several theropods including Dilophosaurus, Kayentavenator,[22] the "Shake-N-Bake" theropod,[clarification needed] the basal sauropodomorphs Sarahsaurus [15] and Anchisaurus, heterodontosaurids, and the armored dinosaurs Scelidosaurus and Scutellosaurus. The Kayenta Formation has produced the remains of three coelophysoid taxa of different body size, representing the most diverse ceratosaur fauna yet known.[16] The formation has also yielded a small but growing assemblage of organisms.[23] Vertebrates present in the Kayenta Formation at the time of S. kayentakatae included hybodont sharks, indeterminate bony fish, lungfish, salamanders, the frog Prosalirus, the caecilian Eocaecilia, the turtle Kayentachelys, a sphenodontian reptile, various lizards, and the pterosaur Rhamphinion. Also present were the synapsids Dinnebitodon, Kayentatherium, Oligokyphus, morganucodontans,[24] the possible early true mammal Dinnetherium, and a haramiyid mammal. Several early crocodylomorphs were also present, including Calsoyasuchus, Eopneumatosuchus, Kayentasuchus, and Protosuchus.[23][24][25][26] Vertebrate trace fossils from this area include coprolites[27] and the tracks of therapsids, lizard-like animals, and dinosaurs.[28] Non-vertebrates in this ecosystem included microbial or "algal" limestone,[27] freshwater bivalves, freshwater mussels and snails,[21] and ostracods.[29] The plant life known from this area included trees that became preserved as petrified wood.[25]

Taphonomy

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The holotype (MNA V2623) of "Syntarsus" kayentakatae came to rest on its left side and was partially buried. This served to stabilize the bones on the left side of the skull; however, the right side of the skull was likely exposed to water currents as it began to decompose. Some of the loosely connected bones on this side drifted out of place before the entire skull was finally buried. Later, the great weight of overlying sediment served to distort the specimen.[30]

References

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  1. ^ a b Bristowe, A. & Raath, M.A. (2004). "A juvenile coelophysoid skull from the Early Jurassic of Zimbabwe, and the synonymy of Coelophysis and Syntarsus". Palaeontologia Africana. 40: 31–41.
  2. ^ "Syntarsus kayentakatae". Global Biodiversity Information Facility. Retrieved 13 April 2022.
  3. ^ Gaines, Richard M. (2001). Coelophysis. ABDO Publishing Company. p. 4. ISBN 1-57765-488-9.
  4. ^ a b Ivie, Michael; Slipinski, Adam; Węgrzynowicz, Piotr (2001). "Generic Homonyms in the Colydiinae (Coleoptera: Zopheridae)". Insecta Mundi.
  5. ^ McDavid, Skye N; Bugos, Jeb E (2022-08-02). "Taxonomic notes on Megapnosaurus and 'Syntarsus' (Theropoda: Coelophysidae)". The Mosasaur (12): 1–5. doi:10.5281/zenodo.7027378.
  6. ^ Padian, K (1997) Glen Canyon Group In: Encyclopedia of Dinosaurs, edited by Currie, P. J., and Padian, K., Academic Press.
  7. ^ Rowe (1989). "A new species of the theropod dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona". Journal of Vertebrate Paleontology. 9 (2): 125–136. Bibcode:1989JVPal...9..125R. doi:10.1080/02724634.1989.10011748.
  8. ^ Tykoski, 1998. The osteology of Syntarsus kayentakatae and its implications for ceratosaurid phylogeny. Unpublished Masters Thesis, University of Texas at Austin, 217 pp.
  9. ^ Gay, 2010. Notes on Early Mesozoic theropods. Lulu Press. 44 pp.
  10. ^ a b Mortimer, Mickey. "Coelophysoidea". Archived from the original on 4 May 2013. Retrieved 15 April 2013.
  11. ^ a b Rowe, (1989). A new species of the theropod dinosaur Syntarsus from the Early Jurassic Kayenta Formation of Arizona. Journal of Vertebrate Paleontology. 9, 125-136.
  12. ^ Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 78. ISBN 978-1-78684-190-2. OCLC 985402380.
  13. ^ Tykoski, 1998. The osteology of Syntarsus kayentakatae and its implications for ceratosaurid phylogeny. Unpublished Masters Thesis, University of Texas at Austin, 217 pp.
  14. ^ Gay, 2010. Notes on Early Mesozoic theropods. Lulu Press. 44 pp.
  15. ^ a b Rowe, T. B., Sues, H.-D., and Reisz, R. R. 2011. Dispersal and diversity in the earliest North American sauropodomorph dinosaurs, with a description of a new taxon. Proceedings of the Royal Society B: Biological Sciences 278(1708):1044–1053.
  16. ^ a b Tykoski, R. S., 1998, The Osteology of Syntarsus kayentakatae and its Implications for Ceratosaurid Phylogeny: Theses, The University of Texas, December 1998.
  17. ^ Tykoski, Ronald S. (2005). Anatomy, Ontogeny, and Phylogeny of Coelophysoid Theropods (PhD). University of Texas at Austin.
  18. ^ Marsh, A. D.; Rowe, T. B. (2020). "A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona". Journal of Paleontology. 94 (78): 1–103. Bibcode:2020JPal...94S...1M. doi:10.1017/jpa.2020.14. S2CID 220601744.
  19. ^ Ezcurra, Martín D; Butler, Richard J; Maidment, Susannah C R; Sansom, Ivan J; Meade, Luke E; Radley, Jonathan D (2021-01-01). "A revision of the early neotheropod genus Sarcosaurus from the Early Jurassic (Hettangian–Sinemurian) of central England". Zoological Journal of the Linnean Society. 191 (1): 113–149. doi:10.1093/zoolinnean/zlaa054. hdl:11336/160038. ISSN 0024-4082.
  20. ^ J. M. Clark and D. E. Fastovsky. 1986. Vertebrate biostratigraphy of the Glen Canyon Group in northern Arizona. The Beginning of the Age of the Dinosaurs: Faunal change across the Triassic-Jurassic boundary, N. C. Fraser and H.-D. Sues (eds.), Cambridge University Press 285–301
  21. ^ a b Harshbarger, J. W.; Repenning, C. A.; Irwin, J. H. (1957). Stratigraphy of the uppermost Triassic and the Jurassic rocks of the Navajo country. Professional Paper. Vol. 291. Washington, D.C.: U.S. Geological Survey. doi:10.3133/pp291. S2CID 32010827.
  22. ^ Gay, R. 2010. Kayentavenator elysiae, a new tetanuran from the early Jurassic of Arizona. Pages 27–43 in Gay, R. Notes on early Mesozoic theropods. Lulu Press (on-demand online press).
  23. ^ a b Lucas, S. G.; Heckert, A. B.; Tanner, L. H. (2005). "Arizona's Jurassic fossil vertebrates and the age of the Glen Canyon Group". In Heckert, A. B.; Lucas, S. G. (eds.). Vertebrate paleontology in Arizona. Bulletin. Vol. 29. Albuquerque, NM: New Mexico Museum of Natural History and Science. pp. 95–104.
  24. ^ a b Jenkins, F. A., Jr., Crompton, A. W., and Downs, W. R. 1983. Mesozoic mammals from Arizona: new evidence in mammalian evolution. Science 222(4629):1233–1235.
  25. ^ a b Jenkins, F. A., Jr. and Shubin, N. H. 1998. Prosalirus bitis and the anuran caudopelvic mechanism. Journal of Vertebrate Paleontology 18(3):495–510.
  26. ^ Curtis, K., and Padian, K. 1999. An Early Jurassic microvertebrate fauna from the Kayenta Formation of northeastern Arizona: microfaunal change across the Triassic-Jurassic boundary. PaleoBios 19(2):19–37.
  27. ^ a b Luttrell, P. R., and Morales, M. 1993. Bridging the gap across Moenkopi Wash: a lithostratigraphic correlation. Aspects of Mesozoic geology and paleontology of the Colorado Plateau. Pages 111–127 in Morales, M., editor. Museum of Northern Arizona, Flagstaff, AZ. Bulletin 59.
  28. ^ Hamblin, A. H., and Foster, J. R. 2000. Ancient animal footprints and traces in the Grand Staircase-Escalante National Monument, south-central Utah. Pages 557–568 in Sprinkel, D. A., Chidsey, T. C., Jr., and Anderson, P. B. editors. Geology of Utah's parks and monuments. Utah Geological Association, Salt Lake City, UT. Publication 28.
  29. ^ Lucas, S. G., and Tanner L. H. 2007. Tetrapod biostratigraphy and biochronology of the Triassic-Jurassic transition on the southern Colorado Plateau, USA. Palaeogeography, Palaeoclimatology, Palaeoecology 244(1–4):242–256.
  30. ^ Tykoski, Ron. "Syntarsus kayentakatae Fossil, Theropod Dinosaur". digimorph.org. Retrieved 15 April 2013.
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