Chinshakiangosaurus
- Yunnan, China ( Fengjiahe Formation)
- Chinshakiangosaurus chunghoensis
Chinshakiangosaurus is a genus of dinosaurs and probably one of the most primitive known members of the sauropods. The only way Chinshakiangosaurus chunghoensis comes from the Lower Jurassic of China and is known by a fragmentary skeleton. Chinshakiangosaurus one of the few very primitive sauropod, of which are known skull bones, and is therefore for understanding the early evolution of this group of importance. For example, this species shows evidence of fleshy cheeks, a feature that was true of the precursor forms of sauropods known ( the " prosauropods " ), in sauropods myself but so far could not be detected.
Characteristics and diet
Chinshakiangosaurus was like all sauropods, a large, four-legged herbivore with a long neck and tail. The only known specimen is estimated at a body length of 12 to 13 meters. The fragmentary remains close the dentary ( the tooth-bearing bone of the mandible ) with teeth and different bones of the body skeleton ( Postkranium ) with a. Been described in detail so far only the dental and teeth; the rest of the skeleton requires further scientific processing.
The two halves of the lower jaw were bent in plan view and thus a U-shape running towards each other, resulting in a broad snout. This feature is typical for sauropods - at prosauropods contrast, the lower jaw halves were straight and ran a V-shape toward each other, the muzzle was thus pointed. Paul Upchurch and colleagues ( 2007) draw conclusions about the diet: The pointed snout of prosauropods could indicate that these animals only certain parts of plants specifically chose to feed ( concentrate selector ), while the broad muzzle could display at Chinshakiangosaurus and most sauropods, that these animals recordings untargeted large amounts of plant material ( eng. bulk browsing ).
While prosauropods typically show a toothless gap between the front teeth and the tip of the lower jaw, this gap is not present in Chinshakiangosaurus and sauropods. The tooth size increased to the snout tip, as in sauropods. Also typical for sauropods is a lateral bony plate that ran along the outside of the teeth and became increasingly more to the snout tip. According to Upchurch and colleagues ( 2007) prevented this bone plate so that the teeth when defoliating plants were put out of position.
The dentary is deep; as in the prosauropods but the depth assumes that bone from tip of the snout to where he ( the seam of the lower jaw halves ) reached the greatest depth in the sauropods at the symphysis. Viewed from the side showing the dental a higher ridge, which runs from the upper edge of the rear end of the bone from diagonally to the front. This feature is otherwise known only for " prosauropods ", where it is interpreted as an approach instead of a fleshy cheek. Such jaw would have prevented food fell out while eating from the mouth, and may indicate that the food has been processed orally to a certain degree before swallowing. Should the classification of Chinshakiangosaurus as original sauropod confirmed, this would be the first indication of fleshy cheeks even with very primitive sauropod.
On each side of the lower jaw were probably 19 teeth - more than in all known sauropods, but less than in the " prosauropods " Plateosaurus. The teeth are filled with coarse teeth and lanceolate; so that they resemble those of the prosauropods more than the spoon-shaped teeth typical sauropods. The tooth enamel is folded, a typical feature of sauropods - at prosauropods it is smooth. The facing to the tongue side of the teeth is slightly concave, possibly an initial stage towards the strongly concave and thus spoon-shaped teeth of later sauropods.
System
Chinshakiangosaurus
Dong Zhiming Chinshakiangosaurus classified initially as a representative of the Melanorosauridae, which he considers to be representative of the " prosauropods " but noted that the teeth resemble those of sauropods. Recent studies, however, consider this genus as an original sauropods. The genus stands as one of the most original known sauropods at the base of the family tree of this group. However, the exact relationships are unknown.
Discovery
The fossils were discovered in 1970 by Zhao Xijin and colleagues in a circle Yongren ( W.-G. Yung -jen ) in the central Yunnan. The site belongs to the lower part of the Fengjiahe lineup, which, siltstones and sandstones consists of reddish mudstone, which were probably deposited fluvolakustrin ( by rivers and within lakes). The age can be dated on the basis of aquatic fossils of invertebrates such as ostracods and shells on the Lower Jurassic; a more precise dating is not possible.
The holotype specimen ( IVPP V14474 copy number ) consists of a left dentary, a few vertebrae ( cervical, dorsal, and caudal vertebrae ), two shoulder blades, some pelvic bone, and the hind legs. CH Ye (1975 ) named this skeleton as Chinshakiangosaurus chunghoensis ( after the river Jinsha Jiang and the community Zhonghe ( W.-G. Chung -ho) in a circle Yongren ), but without publishing a description of why the new name initially as a noun nudum ( ' naked name ' ) had to be performed. Only in 1992 offered Dong Zhiming, a brief description of the fossils, so the name was valid - the authorship of the name has since been correctly as " Chinshakiangosaurus chunghoensis Ye vide Dong 1992 " quotes.
According to the description by Dong the Fund remained long unnoticed. However, Upchurch and colleagues ( 2004) declared the genus as a noun dubium ( " dubious name " ), they already classified within the sauropods. 2007 Upchurch and colleagues published a comprehensive re-examination of the mandible and recognize Chinshakiangosaurus as valid genus.