Monolophosaurus was a
genusIn 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 theropod
dinosaurDinosaurs 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
JurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
(about 168-161 Ma) of the
Shishugou FormationThe Shishugou Formation is a geological formation in Xinjiang, China, whose strata date back to the Late Jurassic period. Dinosaur remains are among the fossils that have been recovered from the formation....
in what is now
XinjiangXinjiang is an autonomous region of the People's Republic of China. It is the largest Chinese administrative division and spans over 1.6 million km2...
,
ChinaChinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. It was named for the single crest on top of its skull. The
typeA 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...
and only known individual is estimated at 5 metres (16.4 ft). The area that
Monolophosaurus was found showed signs of water, so it is possible that this dinosaur lived on the shore of lakes or ocean. The
Monolophosaurus jiangi IVP 84019 had its 10th and possibly 11th neural spines fractured. The tenth is fused to the eleventh. A series of parallel ridges on one of the specimen's dentaries may represent tooth marks.
Discovery and classification
A nearly complete
skeletonThe skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
was unearthed in 1984. At first, before description in the scientific literature, it was known in the press as "Jiangjunmiaosaurus", a
nomen nudumThe phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
.
In 1993 Zhao and Currie named the
type speciesIn biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
Monolophosaurus jiangi; the species name refers to Jiangjunmiao ("an abandoned desert inn") near which the
holotypeA 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...
IVPP 84019 was found.
Monolophosaurus was originally termed a "
megalosaurMegalosauroidea is a group of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period.-Classification:...
" and has often since been suggested to be an
allosauroidAllosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Sinraptoridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae...
. Carr (2006) even suggested that the "
proceratosauridProceratosauridae is a family or clade of theropod dinosaurs, probably belonging to the tyrannosaur lineage. It was first named in 2010 by Oliver Rauhut and colleagues in their re-evaluation of the type genus, Proceratosaurus...
" "
tyrannosauroidTyrannosauroidea is a superfamily of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent beginning in the Jurassic Period...
"
GuanlongGuanlong was a genus of proceratosaurid tyrannosauroid dinosaur, one of the earliest known examples of the lineage.-Description and discovery:...
was a subadult
Monolophosaurus and therefore an "
allosauroidAllosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Sinraptoridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae...
", by noting both taxa have a large, thin, and fenestrated midline crest, but this is probably not the case.
Smith
et al. (2007) was the first publication to find
Monolophosaurus to be a non-neotetanuran tetanuran, by noting many characters previously thought to be exclusive of Allosauroidea to have a more wider distribution. Also, Zhao
et al. (2009) noted various primitive features of the skeleton suggesting that
Monolophosaurus could be one of the most basal
tetanuranTetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
dinosaurs instead. Benson (2008, 2010) placed
Monolophosaurus in a
cladeA clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
with
ChuandongocoelurusChuandongocoelurus named after the Chuandong in Sichuan Province, China, was a genus of tetanuran theropod dinosaur first described by Chinese paleontologist He in 1984...
that is more basal than Megalosauridae and
SpinosauridaeSpinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look...
in the Megalosauroidea. Latter, Benson
et al. (2010) found the
Chuandongocoelurus/
Monolophosaurus clade to be outside of Megalosauroidea and Neotetanurae, near the base of Tetanurae.
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