''Eomamenchisaurus'' (meaning "dawn ''

Mamenchisaurus ''Mamenchisaurus'' ( , or spelling pronunciation ) is an extinct genus of sauropod dinosaurs known for their remarkably long necks which made up nearly half the total body length. Numerous species have been assigned to the genus; however, the val ...

''") is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of mamenchisaurid

sauropod Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

from the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

Zhanghe Formation of

Yuanmou Yuanmou County (; Chuxiong Yi script: , IPA: ) is under the administration of the Chuxiong Yi Autonomous Prefecture, in the north of Yunnan province, China. It borders Wuding County to the east, Lufeng, Yunnan to the south, Dayao County to the we ...

Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

is ''E. yuanmouensis'', described by

Lü Junchang Lü Junchang (; 1965 – 9 October 2018) was a Chinese palaeontologist and professor at the Institute of Geology, Chinese Academy of Geological Sciences. An expert on Mesozoic reptiles, he described and named dozens of dinosaur and pterosaur taxa ...

and colleagues in 2008.

Discovery and naming

''Eomamenchisaurus yuanmouensis'' was named by

, Li Tianguang, Zhong Shimin, Ji Qiang, and Li Shaoxue in 2008 based on a partial skeleton found in Jiangyi Township of

Yuanmou County Yuanmou County (; Yi script, Chuxiong Yi script: , International Phonetic Alphabet, IPA: ) is under the administration of the Chuxiong Yi Autonomous Prefecture, in the north of Yunnan province, China. It borders Wuding County to the east, Lufeng, ...

. The genus name is derived from Greek ἠώς, "dawn" and the name of the related genus ''Mamenchisaurus'', referring to its status as an early mamenchisaurid, and the species name refers to its discovery in Yuanmou.

Fossil record

''Eomamenchisaurus yuanmouensis'' is only known from a single partial skeleton, the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

CXMVZA 165, which includes incomplete

cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...

dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

, a partial

sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

consisting of three preserved vertebrae, the right ilium, pubis, and

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

, and both

femora The femur (; : femurs or femora ), or thigh bone is the only bone in the thigh — the region of the lower limb between the hip and the knee. In many four-legged animals the femur is the upper bone of the hindleg. The top of the femur fits in ...

and

ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from the city of Naples. It is the largest of the Phlegrean Islands. Although inhabited since the Bronze Age, as a Ancient G ...

. The specimen was collected from the Zhanghe Formation, which dates to the

. The specimen is stored in the Chuxiong Museum.

Description

''Eomamenchisaurus'' was a mamenchisaurid, a group of sauropods typically characterized by a very long neck. However, in several respects, ''Eomamenchisaurus'' shows more primitive characteristics than other mamenchisaurids. Like some other mamenchisaurids, the posterior dorsal vertebrae are fused together. The dorsal vertebrae are unlike more derived mamenchisaurids in having only weakly convex anterior faces. The sacrum was probably composed of four vertebrae, as the first preserved sacral vertebra shows a missing sacral vertebra would have attached in front. The femur is long, similar in length to the long femur of the long '' Mamenchisaurus youngi''. The

fourth trochanter The fourth trochanter is a shared characteristic common to archosaurs. It is a protrusion on the posterior-medial side of the middle of the femur shaft that serves as a muscle attachment, mainly for the '' musculus caudofemoralis longus'', the m ...

, a ridge on the femur for muscle attachment, is located on the medial margin of the shaft, as in most early sauropods, rather than being on the midline of the shaft as in ''Mamenchisaurus''. The length of the tibia is approximately 64% of the length of the femur.

Classification

Lü and colleagues, in their original description of ''Eomamenchisaurus'', classified it as a mamenchisaurid. In 2015, Xing Lida and colleagues noted that ''Eomamenchisaurus'' was difficult to distinguish from ''

Yuanmousaurus ''Yuanmousaurus'' ("Yuanmou lizard") was a sauropod dinosaur from the Middle Jurassic period of China. It is known from incomplete remains, recovered in 2000 from the Zhanghe Formation in Yuanmou County in Yunnan Province. ''Yuanmousaurus'' was ...

'', another mamenchisaurid from the Zhanghe Formation.

References

{{Taxonbar, from=Q136000 Mamenchisauridae Dinosaur genera Middle Jurassic dinosaurs Fossil taxa described in 2008 Taxa named by Lü Junchang Dinosaurs of China