Chinshakiangosaurus

Chinshakiangosaurus
Temporal occurrence
Lower Jurassic
201.3 to 174.1 million years
Locations
Yunnan , China ( Fengjiahe Formation )
Systematics
Dinosaur (dinosauria) Lizard dinosaur (Saurischia) Sauropodomorpha Sauropods (Sauropoda) Chinshakiangosaurus
Scientific name
Chinshakiangosaurus
Ye vide Dong , 1992
Art
Chinshakiangosaurus chunghoensis

Chinshakiangosaurus is a genus of dinosaurs and probably one of the most original known representatives of the sauropods . The only species Chinshakiangosaurus chunghoensis comes from the Lower Jurassic of China and is known for its fragmentary skeleton. Chinshakiangosaurus is one of the few very pristine sauropods known to have skull bones, and is therefore important in understanding the early evolution of this group. For example, this genus shows evidence of fleshy cheeks, a feature that was known from the precursor forms of the sauropods (the " prosauropods "), but has not yet been detected in sauropods themselves.

Characteristics and diet

Like all sauropods, Chinshakiangosaurus was a large, four-legged herbivore with a long neck and tail. The only known specimen is estimated to be 12 to 13 meters long. The fragmentary remains include the dental (the tooth-bearing bones of the lower jaw) with teeth and various bones of the body skeleton ( post-cranium ). So far, only the dental and teeth have been described in detail; the rest of the skeleton requires further scientific processing.

The two halves of the lower jaw were curved in plan view and thus ran towards each other in a U-shape, which led to a wide snout. This feature is typical for sauropods - in prosauropods, on the other hand, the lower jaw halves were straight and converged in a V-shape, so the snout was pointed. Paul Upchurch and colleagues (2007) draw conclusions about the diet: The pointed snout of the prosauropods could indicate that these animals selected only certain parts of the plant to eat ( selectors ), while the broad snout of Chinshakiangosaurus and most sauropods could indicate that these animals ingested large amounts of plant material in an untargeted manner ( bulk browsing ).

While prosauropods typically show a toothless gap between the front teeth and the tip of the lower jaw, this gap is absent in Chinshakiangosaurus and the sauropods. The tooth size increased towards the tip of the snout, as with the sauropods. Also typical of sauropods is a lateral bony plate that ran along the outside of the row of teeth and became increasingly stronger towards the tip of the snout. According to Upchurch and colleagues (2007), this bone plate prevented the teeth from being dislodged when defoliating plants.

The dentary is deep; As with the prosauropods, however, the depth of this bone decreases towards the tip of the snout, where it reached the greatest depth in the sauropods at the symphysis (the seam between the halves of the lower jaw). When viewed from the side, the dental shows a distinct ridge that runs diagonally forward from the upper edge of the posterior end of the bone. This feature is otherwise only known in "prosauropods", where it is interpreted as the attachment point of a fleshy cheek. Such a cheek would have prevented food from falling out of the mouth while eating and could indicate that the food was being processed orally to some extent before swallowing. If the classification of Chinshakiangosaurus as an original sauropod is confirmed, this would be the first indication of fleshy cheeks even in very original sauropods.

On each side of the lower jaw there were probably 19 teeth - more than in all known sauropods, but fewer than in the "prosauropod" Plateosaurus . The teeth are lanceolate and covered with coarse teeth; thus they resemble those of prosauropods more than the spoon-shaped teeth of typical sauropods. The enamel, on the other hand, is folded, a typical feature of sauropods - in prosauropods it is smooth. The side of the teeth facing the tongue is also slightly concave, possibly an initial stage towards the strongly concave and thus spoon-shaped teeth of later sauropods.

Systematics

Cladogram , simplified from Upchurch and colleagues, 2007:
Sauropoda    Anchisaurus        Melanorosaurus        Antetonitrus        Chinshakiangosaurus        Isanosaurus        Kotasaurus        Vulcanodon      Shunosaurus        Omeisaurus      Neosauropoda
Systematic position of Chinshakiangosaurus

Dong Zhiming initially classifies Chinshakiangosaurus as a member of the Melanorosauridae , which he considers to be members of the " prosauropods ", but notes that the teeth resemble those of the sauropods. However, recent studies consider this genus to be an original sauropod. The genus is one of the most original known sauropods at the base of the family tree of this group. However, the exact family relationships are unknown.

Find

The fossils were discovered in 1970 by Zhao Xijin and colleagues in Yongren County ( W.-G. Yung-jen ) in central Yunnan . The site belongs to the lower part of the Fengjiahe Formation , which consists of reddish claystones , siltstones and sandstones , which were probably deposited fluvolakustrin (by rivers and within lakes). The age can be dated to the Lower Jurassic using fossils of aquatic invertebrates such as ostracods and mussels; a more precise dating is currently not possible.

The holotype specimen (specimen number IVPP V14474) consists of a left dental, a few vertebrae (cervical, dorsal and caudal vertebrae), both shoulder blades, some pelvic bones and the hind legs. CH Ye (1975) named this skeleton as Chinshakiangosaurus chunghoensis (after the Jinsha Jiang River and the Zhonghe ( W.-G. Chung-ho ) community in Yongren County), but without publishing a description, which is why the new name was initially used as a noun nudum ("naked name") had to be carried out. It was not until 1992 that Dong Zhiming offered a brief description of the fossils, which made the name valid - the authorship of the name has since been correctly quoted as " Chinshakiangosaurus chunghoensis Ye vide Dong, 1992".

After Dong's description, the find went unnoticed for a long time. Upchurch and colleagues (2004) declared the genus as the noun dubium ("dubious name"), but classified it within the sauropods. In 2007, Upchurch and colleagues published a more extensive re-examination of the lower jaw and recognized Chinshakiangosaurus as a valid genus.

Individual evidence

1. ↑ ^{a b c d e f g h i j k l m} Paul Upchurch , Paul M. Barrett , Zhao Xijin , Xu Xing : A re-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992 (Dinosauria, Sauropodomorpha): implications for cranial evolution in basal sauropod dinosaurs. In: Geological Magazine. Vol. 144, No. 2, 2007, ISSN 0016-7568 , pp. 247-262, doi : 10.1017 / S0016756806003062 .  
2. ^ ^{A b} Dong Zhiming : Dinosaurian Faunas of China. China Ocean Press et al., Beijing et al. 1992, ISBN 0-387-52084-8 , p. 48.
3. ^ E. Buffetaut : A new sauropod dinosaur with prosauropod-like teeth from the Middle Jurassic of Madagascar . In: Bulletin de la Societe Geologique de France . tape 176 , no. 5 , 2005, p. 467-473 ( [1] ).
4. ↑ Peter M. Galton , Paul Upchurch: Prosauropoda. In: David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 232-258, here p. 242.
5. ^ Paul Upchurch, Paul M. Barrett, Peter Dodson: Sauropoda. In: David B. Weishampel, Peter Dodson, Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 259-324, here p. 271.
6. ↑ ^{a b} Saswati Bandyopadhyay, David D. Gillette, Sanghamitra Ray, Dhurjati P. Sengupta: Osteology of barapasaurus tagorei (Dinosauria: Sauropoda) from the Early Jurassic of India. In: Palaeontology. Vol. 53. No. 3, 2010, ISSN  0031-0239 , pp. 533-569, here pp. 535 and 562, doi : 10.1111 / j.1475-4983.2010.00933.x .
7. ↑ in Paul Upchurch, Paul M. Barrett, Zhao Xijin, Xu Xing: A re-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992 (Dinosauria, Sauropodomorpha): implications for cranial evolution in basal sauropod dinosaurs. In: Geological Magazine. Vol. 144, No. 2, 2007, pp. 247–262, given as “Yungyin”, but identifiable as Yongren using the coordinates “26.2 ° North, 101.4 ° East”.