|Upper Jurassic ( Oxfordian to Tithonian )|
|163.5 to 145 million years|
|Young , 1954|
Mamenchisaurus is a genus of sauropod dinosaur thatlivedin China during the Upper Jurassic . Mamenchisaurus is known to the publicin particular because of its extremely long neck, which made up half the total length of the animal and consisted of up to 19 cervical vertebrae, more than any other sauropod.
The first find, a partial skeleton without a skull, was discovered in 1952 on a road construction site in the province of Sichuan and described in 1954 by the famous Chinese paleontologist CC Yong as the Mamenchisaurus constructus . Since then, numerous other finds have been described - most studies currently distinguish a total of six species.
The name Mamenchisaurus (Mǎménxī 马 门 溪, from 马 Mǎ (horse), 门 mén (gate) and 溪 xī (stream, stream)) is a wrong spelling of Mǎmíngxī (马鸣 溪), a river ferry on the Jinsha Jiang River (金沙江) near Yibin (宜宾) in Sichuan, which is near the construction site where the first skeleton was discovered.
Mamenchisaurus was a great representative of the sauropods. While the type species Mamenchisaurus constructus, known only from a single skeleton , is estimated to have a total length of 13 meters, Mamenchisaurus hochuanensis was probably significantly larger; the largest specimen of this species discovered was an estimated 22 meters long. Weight estimates of this specimen vary between 14.3 and 18.17 tons, depending on the study. Mamenchisaurus sinocanadorum and Mamenchisaurus jingyanensis could have been up to 26 meters long - but these species have only been passed on through very fragmentary skeletons.
A complete skull is only known from the species Mamenchisaurus youngi . This skull was extremely small in relation to the body - including the lower jaw, it was 51.0 cm long, 19.8 cm wide and 40.1 cm high, with a neck length of almost 6 meters. The brain cavity of this skull showed a volume of only about 60 milliliters. Overall, the skull was similar to that of the Camarasaurus , but was thinner and longer. Well-defined scleral rings around the eyes indicate a good sense of sight. The lower jaw was relatively deep at the front ( symphysis ) and showed a small opening at the side (external mandibular window) - this opening was closed in all other sauropods except Shunosaurus . The chisel-like teeth were close together. In the upper jaw there were between 14 and 18 teeth on each side and 4 teeth in the premaxillary located in front of the upper jaw . The lower jaw, meanwhile, contained between 18 and 24 teeth on each side.
The spine consisted of 18 to 19 cervical vertebrae, 12 vertebrae, 4 to 5 sacral vertebrae and over 50 caudal vertebrae. The neck was one of the relatively longest of all sauropods and was more than three times as long as the body, the largest known specimen of Mamenchisaurus hochuanensis measured the neck over 9.8 meters in length. Only the remains of the related genus Omeisaurus suggest an even longer neck in relation to the total length. The cervical vertebrae were characterized by very long cervical ribs , which ran down the cervical spine and reached a length of up to 4.1 meters in Mamenchisaurus sinocanadorum . Whether Mamenchisaurus just kept its neck horizontal or was able to straighten it up like a giraffe in order to be able to graze at greater heights is a matter of dispute. A more recent biomechanical study notes, however, that the neck was too immobile to straighten because of the very long neck ribs - unlike representatives of the Diplodocidae , whose neck was significantly more mobile and possibly allowed it to be straightened. The spine resembled that of the Diplodocidae in other features: the spinous processes of the posterior cervical and anterior vertebrae were bifurcated; in addition, the middle caudal vertebrae bore typical double-bar-like chevron bones .
The vertebrae in front of the sacrum were opisthocoel , that is, convex on the front and concave on the back. The caudal vertebrae close to the body showed the opposite constellation ( procoel - concave on the front and convex on the rear), while the middle caudal vertebrae were amphiplat (flat on the front and rear). Further features relevant to the delimitation of the genus can also be found in the shoulder girdle and the extremities: The shovel-like lower end of the shoulder blade was enlarged, the entire bone was longer than the thigh bone. The sternum was small and roughly round. The length ratio between the front and rear legs was about 3/4 to 4/5, both the front and rear feet were relatively small.
|Cladogram , simplified according to Sander and colleagues (2010):|
|Systematic position of Mamenchisaurus according to Sander and colleagues (2010)|
The systematic classification of Mamenchisaurus is controversial. John McIntosh (1990) considered the genus to be a representative of the Diplodocidae , based on the double-bar-like chevron bones, the forked spinous processes and the procoel caudal vertebrae. Later it turned out, however, that these characteristics are not only found in representatives of the Diplodocidae, but also in many other sauropod groups. Paul Upchurch (1995, 1998, 1999), however , assigned Mamenchisaurus to the Euhelopodidae - this grouping is now considered paraphyletic , since Euhelopus is only distantly related to Mamenchisaurus .
Today Mamenchisaurus is considered to be an original representative of the Eusauropoda , which, however, lacked important features of the more advanced sauropods ( Neosauropods ) and which is therefore outside of the Neosauropoda. Often Mamenchisaurus is classified together with presumably closely related forms within a group called Mamenchisauridae . Which genera are to be assigned to this group in addition to Mamenchisaurus is disputed - however, the genera Chuanjiesaurus , Eomamenchisaurus , Tienshanosaurus , Tonganosaurus , Omeisaurus and Yuanmousaurus are often placed in this group.
Paul Upchurch (2004) notes that the internal system of Mamenchisaurus is very confusing and that the genus needs revision. Many of the finds known as Mamenchisaurus cannot be assigned to this genus with certainty (trash taxon).
Six species are currently recognized; some studies list a possible seventh species, Mamenchisaurus fuxiensis , but its status is unclear.
- Mamenchisaurus constructus Young, 1954 : The type species is based on a single, incomplete skeleton, the skull, shoulder girdle and front legs are missing and which belonged to an approximately 13 meter long specimen. The skeleton comes from the Shangshaximiao Formation of Yibin in Sichuan .
- Mamenchisaurus hochuanensis Young & Zhao, 1972 : This species is known from at least five skeletons, one of these specimens includes remains of the skull. A completely traditional neck consists of 19 cervical vertebrae. The largest specimen is estimated to be 22 meters long. The skeletons come from the Shangshaximiao Formation of Hechuan and Zigong in Sichuan and from the Hengtang Formation of Yongdeng in Gansu .
- Mamenchisaurus sinocanadorum Russell & Zheng, 1994 : A very large species known only from a series of cervical vertebrae with an incomplete skull that comes from the Shishugou formation of Jungger in Xinjiang .
- Mamenchisaurus youngi Pi, Ouyang & Ye, 1996 : A single, but almost complete skeleton with a complete skull is known of this species. This specimen is estimated to be 16 meters long. It comes from the Shangshaximiao Formation of Zigong in Sichuan.
- Memenchisaurus anyuensis He et al. , 1996 : One relatively complete and four incomplete skeletons are known, which are estimated to be about 21 to 23 meters in length. These finds come from the Penglaizheng Formation of Anyue in Sichuan.
- Mamenchisaurus jingyanensis Zhang, Li & Zeng, 1998 : This species is known for having three incomplete skeletons - one of these skeletons includes an incomplete skull. The length of these specimens is estimated to be 20 to 26 meters. The finds come from the Shangshaximiao Formation of Jingyan in Sichuan.
- Mamenchisaurus fuxiensis (Hou, Zhao, & Chao, 1976) : This problematic species was originally described as a separate genus - Zigongosaurus . However, it may be a species of Omeisaurus or Mamenchisaurus . The only find consists of various, disjointed bones from the Shangshaximiao Formation of Zigong in Sichuan.
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