Stegosauria

Taxobox
name = Stegosaurians
fossil_range = Middle Jurassic - Early Cretaceous

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image_width = 200px
image_caption = Fossil skeleton of a "Stegosaurus",
National Museum of Natural History
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Thyreophora
infraordo = Stegosauria
infraordo_authority = Marsh, 1877
subdivision_ranks = Families
subdivision =
Huayangosauridae
Stegosauridae

Known colloquially as stegosaurs, the Stegosauria are a group of herbivorous dinosaurs of the Jurassic and Early Cretaceous Periods, being found mostly in the Northern Hemisphere, predominantly in what is now North America and China. Their geographical origins are unclear; the earliest stegosaurs have been found in China, although fragmentary material hails from southern England.

The genus "Stegosaurus", from which the group acquires its name, is by far the most famous stegosaurian.

Paleobiology

All stegosaurs have rows of special bones, called osteoderms, which develop into plates and spines along the back and tail. Many also have intermediate ones, called 'splates'.

kull

They had characteristic long, narrow heads and a horn-covered beak or rhamphotheca, which covered the front of the upper jaw (premaxillary) and lower jaw (predentary) bones. Similar structures are seen in turtles and birds. Apart from "Huayangosaurus", stegosaurs subsequently lost nearby premaxillary teeth. [Sereno, P & Z-M Dong (1992). The skull of the basal stegosaur "Huayangosaurus taibaii" and a cladistic diagnosis of Stegosauria. "Journal of Vertebrate Paleontology" 51: 318-343]

Posture

All are quadrupedal, with hoof-like toes on all four limbs. All stegosaurians after "Huayangosaurus" have forelimbs much shorter than their hindlimbs. Given that their speed would have been limited by their shortest limb and their size is likely to have precluded them from being bipedal, this suggests that they were not able to run quickly.

Taxonomy

The Stegosauria was originally named as an order within Reptilia by O.C. Marsh in 1877,Marsh, O.C. (1877). "New order of extinct Reptilia (Stegosauria) from the Jurassic of the Rocky Mountains." "American Journal of Science", 14(ser.3):513-514.] although today it is generally treated as an infraorder or suborder (or simply a clade) within Thyreophora, the armored dinosaurs. It includes the families Huayangosauridae and Stegosauridae.

The Huayangosauridae were an early family of stegosaurs which lived during the early to middle Jurassic Period. In general, they were smaller than later stegosaurs and had shorter and higher skulls. Currently, the only confirmed genus included is the type genus "Huayangosaurus" of China. The poorly-known remains of "Regnosaurus" from England, however, indicate it too could be a member. Its lower jaw is very similar to the former.

The vast majority of Stegosaurian dinosaurs thus far recovered being to the Stegosauridae, which lived in the later part of the Jurassic and early Cretaceous. It includes the well-known "Stegosaurus". The family is widespread, with members across the Northern Hemisphere and Africa.

Classification

Following is a list of stegosaurian genera by classification and location:

Suborder Thyreophora

Infraorder Stegosauria
* "Gigantspinosaurus"
* Family Huayangosauridae
** "Huayangosaurus" (Sichuan,China)
**?"Regnosaurus" (Sussex, United Kingdom)
* Family Stegosauridae
** "Paranthodon" - (South Africa)
** "Monkonosaurus" - (Tibet, China)
** "Chungkingosaurus" - (Chongqing, China)
** "Chialingosaurus" - (Sichuan, China)
** "Wuerhosaurus" - (Xinjiang, Western China)
** "Hesperosaurus" - (Wyoming, USA)
** "Dacentrurus" - (United Kingdom, France & Spain)
** Subfamily Stegosaurinae
*** "Tuojiangosaurus" - (Sichuan, China)
*** "Kentrosaurus" - (Tanzania, Africa)
*** "Lexovisaurus" (="Loricatosaurus")cite journal |last=Maidment |first=Susannah C.R. |coauthors=Norman, David B.; Barrett, Paul M.; and Upchurch, Paul |year=in press |title=Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia) |journal=Journal of Systematic Palaeontology |doi=doi:10.1017/S1477201908002459] - (United Kingdom & France)
*** "Stegosaurus" - (Wyoming, USA)
** Uncertain placement ("incertae sedis")
*** ?"Craterosaurus" - (Bedfordshire, England)
***"Jiangjunosaurus" - (Xinjiang, Western China)

Phylogeny

Kenneth Carpenter of the Denver Museum of Nature and Science published a preliminary phyletic treeCarpenter, K., Miles, C.A., and Cloward, K. (2001). "New Primitive Stegosaur from the Morrison Formation, Wyoming", in Carpenter, Kenneth(ed) "The Armored Dinosaurs". Indiana University Press. ISBN 0-253-33964-2, 55–75.] of stegosaurs, in the 2001 description of "Hesperosaurus". Here, the basal stegosaur "Huayangosaurus" is used as the outgroup. The Stegosauridae are then defined as all stegosaurs closer to "Stegosaurus" than to "Huayangosaurus". The position of "Chungkingosaurus" is uncertain due to lack of data.

Stegosauria
--"Huayangosaurus" `--Stegosauridae `--+-?"Chungkingosaurus" `--+--"Chialingosaurus" `--+--+--"Wuerhosaurus"
`--+--"Dacentrurus"
`--"Hesperosaurus" `--+--"Tuojiangosaurus" `--+--+--"Kentrosaurus"
`--"Lexovisaurus" `--+--"Stegosaurus stenops" `--"S. ungulatus" (=?"S. armatus")

Undescribed species

To date, several genera from China bearing names have not been formally described, including "Changdusaurus" and "Yingshanosaurus". Until formal descriptions are published, these genera are regarded as "nomina nuda".

References

*

External links

* http://www.palaeos.com/Vertebrates/Units/320Ornithischia/320.200.html
* http://www.kheper.net/evolution/dinosauria/Stegosauria.htm