Chilesaurus

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Chilesaurus
Temporal range: Late Jurassic
145 Ma
Chilesaurus diegosarezi.jpg
Reconstructed skeleton
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Genus: Chilesaurus
Novas et al. 2015
Species: C. diegosuarezi
Binomial name
Chilesaurus diegosuarezi
Novas et al. 2015

Chilesaurus is an extinct genus of herbivorous dinosaur. The type and only species is Chilesaurus diegosuarezi.[1] Chilesaurus lived about 145 million years ago (Mya) in the Late Jurassic period of Chile.

Description[edit]

Life reconstruction of Chilesaurus, size based on holotype individual

Chilesaurus measured roughly 3.2 m (10.5 ft) from nose to tail. The holotype is a smaller individual of half that length.

The most unusual feature of Chilesaurus is its spatula-shaped, elongated teeth, obliquely pointing forwards. Such dentition would be unique in the Theropoda, where it has sometimes been recovered, and is typical for a herbivore, indicating Chilesaurus was a plant-eater. Another adaptation for eating plants is the backward-pointing pubic bone in the pelvis, making room for a large gut. Such a pelvic arrangement is typical for the Ornithischia, which some other studies have allied it with, although is also found in some groups of Theropoda. The hind limb of Chilesaurus had become less adapted to running as shown by a small cnemial crest on the front top of the shinbone, and a broad foot with a weight-bearing first toe. Chilesaurus could defend itself with a strong arm, bearing a large first claw which could be extended outwards, just as with the basal Sauropodomorpha.

Discovery and naming[edit]

Cast of the holotype skeleton

Fossils of Chilesaurus, a vertebra and a rib, were first discovered on 4 February 2004 by the seven-year-old Diego Suárez, who together with his parents, geologists Manuel Suárez and Rita de la Cruz, was searching for decorative stones in the Aysén Region. More specimens were present that in 2008 were reported as representing several dinosaurian species.[2] Only later was it realised that these belonged to a single species with a bizarre combination of traits.

In 2015, the type species C. diegosuarezi was named and described by Fernando Emilio Novas, Leonardo Salgado, Manuel Suárez, Federico Lisandro Agnolín, Martín Dário Ezcurra, Nicolás Chimento, Rita de la Cruz, Marcelo Pablo Isasi, Alexander Omar Vargas, and David Rubilar-Rogers. The generic name refers to Chile. The specific name honours Diego Suárez.[1]

The holotype, SNGM-1935, was found in a layer of the Toqui Formation dating from the late Tithonian. It consists of an articulated, rather complete skeleton with skull of a juvenile individual, lacking the feet and most of the tail. Four other partial skeletons (specimens SNGM-1937, SNGM-1936, SNGM-1938, and SNGM-1888) and several single bones (specimens SNGM-1889, SNGM-1895, SNGM-1901, SNGM-1894, SNGM-1898, SNGM-1900, and SNGM-1903) are the paratypes. They represent juvenile and adult individuals.[1]

Classification[edit]

Skeletal reconstruction

Chilesaurus was first placed in the Tetanurae, in a basal position. It shows a confusing mix of traits normally present in Coelurosauria, basal Sauropodomorpha and Ornithischia, but was found in its original description to belong to none of these groups.[1] Alternatively, Baron and Barrett proposed in 2017 that Chilesaurus may be a basal ornithischian, with orithischians being closer to theropods than sauropodomorphs as a part of the Ornithoscelida.[3][4]

The below cladogram illustrates the taxonomy proposed in the original description of Chilesaurus.[1]

Theropoda


Herrerasauridae




Coelophysoidea




Ceratosauria




Chilesaurus




Megalosauroidea




Allosauroidea



Coelurosauria








Restoration

Below is a cladogram illustrating the newly proposed classification of Chilesaurus as an ornithischian.[3]

Dinosauria



Herrerasauridae



Sauropodomorpha





Theropoda


Ornithischia


Chilesaurus




Pisanosaurus




Neornithischia



Thyreophora







References[edit]

  1. ^ a b c d e Novas, F. E.; Salgado, L.; Suárez, M.; Agnolín, F. L.; Ezcurra, M. N. D.; Chimento, N. S. R.; de la Cruz, R.; Isasi, M. P.; Vargas, A. O.; Rubilar-Rogers, D. (2015). "An enigmatic plant-eating theropod from the Late Jurassic period of Chile". Nature. 522: 331–334. doi:10.1038/nature14307. PMID 25915021. 
  2. ^ Salgado, L.; De La Cruz, R.; Suárez, M.; Gasparini, Z.; Fernández, M. (2008). "First Late Jurassic dinosaur bones from Chile". Journal of Vertebrate Paleontology. 28: 529–534. doi:10.1671/0272-4634(2008)28[529:fljdbf]2.0.co;2. 
  3. ^ a b Baron, Matthew G.; Barrett, Paul M. (2017). "A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs". Biology Letters. The Royal Society. 13 (8). doi:10.1098/rsbl.2017.0220. 
  4. ^ https://www.cam.ac.uk/research/news/study-identifies-dinosaur-missing-link

External links[edit]