Zigongosaurus
Encyclopedia
Zigongosaurus is a genus
of sauropod dinosaur
from the Middle Jurassic
-Late Jurassic
-age Shaximiao Formation of Zigong, Sichuan
, China
. Because of incomplete knowledge of Jurassic Chinese sauropods, it has been hard to interpret, with some sources assigning it to Omeisaurus
, some to Mamenchisaurus
, and some to its own genus.
CV 00261, a specimen including a partial mandible
, maxilla
, and basioccipital (a bone from the braincase region). Additional bones from all areas of the skeleton, belonging to multiple individuals, were also described and assigned to the new genus. The authors thought it resembled Omeisaurus, but was distinct based on vertebral details. Early accounts in the popular press suggested it was a brachiosaurid
.
Chinese sauropod taxonomy became increasingly convoluted in the 1980s. In 1983, Dong, Zhou, and Zhang named a species Omeisaurus fuxiensis, which they based on different material than Zigongosaurus fuxiensis, but then suggested that the two were the same animal. Following this, the genus was thought to belong to Omeisaurus, possibly as a synonym
of O. junghsiensis. In the mid-1990s, opinion shifted, and the genus was instead assigned, by Zhang and Chen, to Mamenchisaurus. They noted that it came from a stratigraphic level
between the usual Omeisaurus and Mamenchisaurus beds
in age, but more closely resembled Mamenchisaurus. In particular, the neural spines
of the vertebrae (the part of the vertebra that sticks up, over the passage for the spinal cord
) in both genera have distinctive weak bifurcation, or splitting, that is not found in Omeisaurus. The authors renamed it Mamenchisaurus fuxiensis. This assignment was followed provisionally in the most recent major review of sauropods, but at least one author (Valérie Martin-Rolland) has found it to be a distinct genus.
with a long neck. It is regarded as a medium- to large-sized sauropod, with a length of around 15 meters (50 feet).
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of sauropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
-Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
-age Shaximiao Formation of Zigong, Sichuan
Sichuan
' , known formerly in the West by its postal map spellings of Szechwan or Szechuan is a province in Southwest China with its capital in Chengdu...
, China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
. Because of incomplete knowledge of Jurassic Chinese sauropods, it has been hard to interpret, with some sources assigning it to Omeisaurus
Omeisaurus
Omeisaurus is a genus of sauropod dinosaur from the Middle Jurassic Period of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation of Sichuan Province.Like other sauropods, Omeisaurus was herbivorous and large...
, some to Mamenchisaurus
Mamenchisaurus
Mamenchisaurus was a plant-eating four-legged dinosaur, known for its remarkably long neck which made up half its total length. It is known from numerous species which ranged in time from 160 to 145 million years ago, from the Oxfordian to Tithonian ages of the late Jurassic Period of...
, and some to its own genus.
History and taxonomy
The genus was based onHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
CV 00261, a specimen including a partial mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
, and basioccipital (a bone from the braincase region). Additional bones from all areas of the skeleton, belonging to multiple individuals, were also described and assigned to the new genus. The authors thought it resembled Omeisaurus, but was distinct based on vertebral details. Early accounts in the popular press suggested it was a brachiosaurid
Brachiosauridae
Brachiosauridae are a family of dinosaurs, whose members are known as brachiosaurids. They were herbivorous quadrupeds with longer forelegs than hind legs - the name derives from the Greek for arm lizard - and long necks...
.
Chinese sauropod taxonomy became increasingly convoluted in the 1980s. In 1983, Dong, Zhou, and Zhang named a species Omeisaurus fuxiensis, which they based on different material than Zigongosaurus fuxiensis, but then suggested that the two were the same animal. Following this, the genus was thought to belong to Omeisaurus, possibly as a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of O. junghsiensis. In the mid-1990s, opinion shifted, and the genus was instead assigned, by Zhang and Chen, to Mamenchisaurus. They noted that it came from a stratigraphic level
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
between the usual Omeisaurus and Mamenchisaurus beds
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
in age, but more closely resembled Mamenchisaurus. In particular, the neural spines
Spinous process
The spinous process of a vertebra is directed backward and downward from the junction of the laminae , and serves for the attachment of muscles and ligaments. In animals without an erect stance, the process points upward and may slant forward or backward...
of the vertebrae (the part of the vertebra that sticks up, over the passage for the spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
) in both genera have distinctive weak bifurcation, or splitting, that is not found in Omeisaurus. The authors renamed it Mamenchisaurus fuxiensis. This assignment was followed provisionally in the most recent major review of sauropods, but at least one author (Valérie Martin-Rolland) has found it to be a distinct genus.
Paleobiology
Whichever genus it turns out to be, as a mamenchisaur- or omeisaur-like sauropod it would have been a large, quadrupedal herbivoreHerbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
with a long neck. It is regarded as a medium- to large-sized sauropod, with a length of around 15 meters (50 feet).