Scelidosaurus

Taxobox
name = "Scelidosaurus"
fossil_range = Early Jurassic

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image_width = 250px
image_caption = "Scelidosaurus"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Thyreophora
infraordo = Ankylosauria
familia = Scelidosauridae
familia_authority = Cope, 1869
genus = "Scelidosaurus"
genus_authority= Owen, 1859
subdivision_ranks=Species
subdivision=
* "S. harrisonii" Owen, 1861 (type)

"Scelidosaurus" (pronEng|ˌsɛlɨdəˈsɔrəs, meaning "limb lizard", from Greek "skelos/σκελος" meaning 'leg' and "saurus/σαυρος" meaning 'lizard')Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4] is a genus of quadrupedal, lightly plated, herbivorous dinosaur about 4 metres long (13 ft). It lived during the Early Jurassic Period, during the Hettangian to Sinemurian stages around 208 to 194 million years ago. Its fossils have been found in both England and in Arizona, in the United States. "Scelidosaurus" has been called the earliest complete dinosaur.Norman, David (2001). "Scelidosaurus", the earliest complete dinosaur" in "The Armored Dinosaurs", pp 3-24. Bloomington: Indiana University Press. ISBN 0253339642.] This genus and related genera have been found on three continents.

Comparative anatomist Richard Owen described "Scelidosaurus" in 1859. Only one species, "S. harrisonii", is considered valid today, although other species have been proposed over the years. One of the most primitive of the thyreophorans, the exact placement of "Scelidosaurus" within the suborder has been the subject of debate for nearly 150 years. This is not helped by the paucity of knowledge about its closest relatives.

Description

A full-grown "Scelidosaurus" was rather small, compared to most other dinosaurs. Some scientists have estimated a length of 4 metres (13 ft) "Scelidosaurus" was quadrupedal, with the hindlimbs considerably longer than the forelimbs. It may have reared up on its hind legs to browse on foliage from trees, but its forefeet were as large as its hind feet, indicating a mostly quadrupedal posture. "Scelidosaurus" had four toes, with the innermost digit being the smallest.

kull

Unlike later ankylosaurs, the skull was low and triangular in shape, longer than it was wide, similar to that of primitive ornithischians. The head of "Scelidosaurus" was small, and it had a neck that was longer than that of most armored dinosaurs.

Like other thyreophorans, "Scelidosaurus" was herbivorous, with very small, leaf-shaped cheek teeth suitable for cropping vegetation. It is believed "Scelidosaurus" fed with a puncture-crush system of tooth-on-tooth action, with simple up-and-down jaw movement.cite book|title=The Armored Dinosaurs|year=2001|chapter=Tooth wear and possible jaw action of "Scelidosaurus harrisoni" Owen and a review of feeding mechanisms in other thyreophoran dinosaurs|editor=Carpenter, Kenneth(ed)|author=Barrett, P.M.|pages=25–52|publisher=Indiana University Press|id=ISBN 0-253-33964-2] Unlike later ankylosaurs, "Scelidosaurus" still had the five pairs of fenestrae (skull openings) seen in primitive ornithischians, and its teeth were more leaf-shaped than later armored dinosaurs.Kazlev, M. Alan (2007). [http://www.palaeos.com/Vertebrates/Units/320Ornithischia/400.html "Ornithischia: Ankylosauromorpha"] Palaeos. Retrieved on 2007-02-11.]

Armor

The most obvious feature of "Scelidosaurus" is its armor, consisting of bony scutes embedded in the skin. These osteoderms were arranged in parallel rows down the animal's body. Osteoderms are also found in the skin of crocodiles, armadillos and some lizards. These osteoderms ranged in both size and shape; most were small, flat plates, but thicker scutes also occurred. The scutes were aligned in regular horizontal rows down the animal's neck, back, and hips, with smaller scutes arranged on the limbs and tail. The lateral scutes were conical, rather than the blade-like osteoderms of "Scutellosaurus", and have been used to identify the genus.Martill, D.M., Batten, D.J., and Loydell, D.K. (2000). A New Specimen of the Thyreophoran Dinosaur CF "Scelidosaurus" with Soft Tissue Preservation. "Palaeontology", Vol. 43, Part 3, 2000, pp. 549-559. DOI: 10.1111/j.0031-0239.2000.00139.x] It also had a pair of distinctive three-pointed scutes behind the head. Compared to later ankylosaurs, "Scelidosaurus" was lightly armored.

Fossilized skin impressions have also been found. Between the bony scutes, "Scelidosaurus" had rounded scales similar to those of a Gila monster.Lambert D (1993). "The Ultimate Dinosaur Book". Dorling Kindersley, New York, 110-113. ISBN 1-56458-304-X] Between the large scutes, very small (5-10 millimetres [0.2-0.4 in] ) flat "granules" of bone were distributed within the skin. In later ankylosaurs, these small scutes may have developed into larger scutes, fusing into the multi-osteodermal plate armor seen in genera such as "Ankylosaurus".

Diet

"Scelidosaurus" and its Jurassic relatives were herbivorous. However, while other ornithischians possessed teeth capable of grinding plant material, "Scelidosaurus" had smaller, less complex teeth and a jaw capable of only simple up-and-down jaw movements. In this aspect, they resembled the stegosaurids, which also bore primitive teeth and simple jaws.cite book|title=The Dinosauria (2nd Edition |year=2004|chapter=Stegosauria|editor=Weishampel DB, Dodson P, Osmólska H |author=Galton PM, Upchurch P|pages=361|publisher=University of California Press|id=ISBN 0-520-24209-2] Also like stegosaurs, they may have swallowed gastroliths to aid processing of food (because of the lack of chewing ability), in the same manner used by modern birds and crocodiles. [ [http://www.dinoruss.com/de_4/5c52ddb.htm Stegosaurs] Jacobson, RJ. Dinosaur and Vertebrate Paleontology Information. Retrieved 2007-02-11.] Their diet would have consisted of leaved plants or fruits, as grasses did not evolve until late into the Cretaceous Period, after "Scelidosaurus" had become extinct.

Classification

"Scelidosaurus" was an ornithischian and has been classified at different times as an ankylosaur or stegosaur. This debate is still ongoing; at this time, it is considered to be either more closely related to ankylosaurids than to stegosaurids and, by extension, a true ankylosaur,cite book|title=The Armored Dinosaurs|year=2001|chapter=Phylogenetic Analysis of Ankylosauria|editor=Carpenter, Kenneth(ed)|author=Carpenter, Kenneth|pages=455–480|publisher=Indiana University Press|id=ISBN 0-253-33964-2] Kazlev, M. Alan (2007). [http://www.palaeos.com/Vertebrates/Units/320Ornithischia/400.html "Ornithischia: Ankylosauromorpha"] Palaeos. Retrieved on 2007-02-11.] or basal to the ankylosaur-stegosaur split.cite book|title=The Dinosauria, 2nd Edition|year=2004|chapter=Basal Thyreophora|editor=Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.)|author=Norman, D.B., Witmer, L.M., and Weishampel, D.B.|pages=335–342|publisher=University of Californian Press|id=ISBN 0-520-24209-2] The stegosaur classifcation has fallen out of favor, but is seen in older dinosaur books.cite book |last=Colbert |first=Edwin H. |authorlink=Edwin Harris Colbert |title=The Age of Reptiles |year=1965 |pages=p. 128 |publisher=W. W. Norton & Company, Inc. |location=New York |ISBN=0486293777] Despite its ankylosaur classification, "Scelidosaurus" shared similarities with "Stegosaurus", including a heavy body highest at the hips and bony plates down its back.

"Scelidosaurus" gives its name to the Scelidosauridae, a group of primitive ornithischians close to the ancestry of ankylosaurs and stegosaurs. Aside from "Scelidosaurus", other members of the clade include "Bienosaurus" and possibly "Scutellosaurus". Originally proposed by Edward Drinker Cope in 1869, the family was resurrected by Chinese paleontologist Dong Zhiming in 2001 after study of "Bienosaurus", which shares close affinities with "Scelidosaurus". The scelidosaurids have been found in Early Jurassic formations, and may have persisted into the Late Jurassic. Their fossils have been found in China, England, and Arizona. Some paleontologists consider the Scelidosauridae paraphyletic, but Benton (2004) lists the group as monophyletic.Benton, M.J. (2004). "Vertebrate Palaeontology" (Third ed.). Blackwell Publishing. ISBN 9780632056378]

Fossil records of thyreophorans more basal than "Scelidosaurus" are sparse. The more primitive "Scutellosaurus", also found in Arizona, was an earlier genus which was facultatively bipedal. A trackway of a possible early armoured dinosaur, from around 195 million years ago, has been found in France. [Le Loeuff, J., Lockley, M., Meyer, C., and Petit, J.-P. (1999). Discovery of a thyreophoran trackway in the Hettangian of central France. "C. R. Acad. Sci. Paris" 2 328, 215-219] Ancestors of these primitive thyreophorans evolved from early ornithischians similar to "Lesothosaurus" during the Late Jurassic.

pecies

"S. harrisonii", described by Owen, is currently the only recognized species, based on several nearly complete skeletons. A potential second species from the Sinemurian-age Lower Lufeng Formation, "S. oehleri", was described by D.J. Simmons in 1965 under its own genus, "Tatisaurus". In 1996 Spencer G. Lucas moved it to "Scelidosaurus".Lucas SG. (1996). The Thyreophoran Dinosaur "Scelidosaurus" from the Lower Jurassic Lufeng Formation, Yunnan, China. pp. 81-85, in Morales, M. (ed.), "The Continental Jurassic". Museum of Northern Arizona Bulletin 60.] Although the fossils are fragmentary, this reassessment has not been accepted, and "S. oehleri" is today once again recognized as "Tatisaurus".cite journal |last=Norman |first=David B. |coauthors=Butler, Richard J.; and Maidment, Susannah C.R. |year=2007 |title=Reconsidering the status and affinities of the ornithischian dinosaur "Tatisaurus oehleri" Simmons, 1965 |journal=Zoological Journal of the Linnean Society |volume=150 |pages=865–874 |doi=10.1111/j.1096-3642.2007.00301.x ]

History of discovery

While James Harrison of Charmouth, England was quarrying the cliffs of Black Ven (between Charmouth and Lyme Regis), possibly for raw material for the manufacture of cement, in 1858, he found a few fragmentary fossils of limb bones. He sent them to Professor Richard Owen of the Natural History Museum (originally the British Museum (Natural History), London). These, with later finds from the same spot, revealed a nearly complete skeleton. "Scelidosaurus" was named by Sir Richard Owen in 1859; however, a complete description did not appear until 1863. Unfortunately, mixed in with the "Scelidosaurus" fossils were the partial remains of a theropod dinosaur; this was not discovered until 1968.Newman, B.H. (1968) The Jurassic dinosaur "Scelidosaurus harrisoni", Owen. "Palaeontology" 11 (1), 40-3.] In 1888, Richard Lydekker selected the knee joint as the lectotype of "Scelidosaurus".For many years, the enigmatic fossils of "Scelidosaurus" caused some debate over the classification of the genus. Von Zittel (1902), Swinton (1934), and Appleby "et al." (1967) identified the genus as a stegosaur.Thulborn, R.A. (1977) Relationships of the lower Jurassic dinosaur "Scelidosaurus harrisonii". Journal of Paleontology. July 1977; v. 51; no. 4; p. 725-739] In a 1968 paper, Romer argued it was an ankylosaur. In 1977, Richard Thulborn of the University of Queensland attempted to reclassify "Scelidosaurus" as an ornithopod similar to "Tenontosaurus" or "Iguanodon".Thulborn, R.A. (1977) Relationships of the lower Jurassic dinosaur "Scelidosaurus harrisonii". Journal of Paleontology. July 1977; v. 51; no. 4; p. 725-739] Thulborn argued "Scelidosaurus" was a lightly-built bipedal dinosaur adapted for running. Thulborn's 1977 theories on the genus have since been rejected.

In 1968, B. H. Newman applied to have Lydekker's selection of the knee joint as the lectotype officially rescinded by the International Commission on Zoological Nomenclature, as the joint was from a megalosaur. Wells "et al." informally reassigned these bones, consisting of a femur and partial tibia, to "Merosaurus" in 1995.Mortimer, M (2004) [http://home.comcast.net/~eoraptor/Tetanurae.htm#Merosaurusnewmani "The Theropod Database"] . University of Washington. Retrieved 2008-08-14.]

In 1989, scutes identified as belonging to "Scelidosaurus", which were found in the Kayenta Formation (Glen Canyon Group) of northern Arizona, helped to determine the age of the strata was around 200 million years ago.Padian, K. (1989). "Presence of the dinosaur "Scelidosaurus" indicates Jurassic age for the Kayenta Formation (Glen Canyon Group, northern Arizona)". "Geology". May 1989, v. 17; no. 5; p. 438-441] These scutes also established a geographic tie-in between Arizona's Glen Canyon and Europe, where fossils of "Scelidosaurus" had previously been discovered. Some scientists have disputed the assignment to "Scelidosaurus", though.

In 2000, Martill "et al." announced the preservation of soft tissue in a specimen of "Scelidosaurus". These fossils consist of eight caudal vertebrae in a cut slab of carbonatemudstone, which was judged to date from the late Hettangian to Sinemurian stages. Parts of the fossil were preserved in such a way that an envelope of preserved soft tissue is visible around the vertebrae, and show the presence of an epidermal layer over the scutes. The authors concluded that the osteoderms of all basal armored dinosaurs were covered in a tough, probably keratinous layer of skin.

In popular culture

Although "Scelidosaurus" is nowhere near as well-known as its sister taxa "Ankylosaurus" or "Stegosaurus", the genus has appeared infrequently in popular media. One instance is in Nintendo's "" video game, where the player controls a menagerie of dinosaurs, including "Scelidosaurus". The dinosaur is also one of the main exhibits at the Charmouth Heritage Coast Centre in Charmouth, England. The center houses both a model and a cast of "Scelidosaurus", fossils of which were collected in the area. The children's show "Harry and His Bucket Full of Dinosaurs" features a "Scelidosaurus" named Sid as one of Harry's dinosaur friends.

References

External links

* [http://www.tolweb.org/Ankylosauromorpha Ankylosauromorpha] at the Tree of Life
* [http://palaeos.com/Vertebrates/Units/320Ornithischia/400.html#Scelidosauridae Scelidosauridae]
* [http://www.dinoruss.com/de_4/5a7758b.htm "Scelidosaurus" in The Dinosaur Encyclopaedia] at Dino Russ's Lair
* [http://www.users.qwest.net/~jstweet1/ornithischia.htm "Scelidosaurus"] at "Thescelosaurus"! (scroll to Thyreophora)
* [http://www.dinodata.org/index.php?option=com_content&task=view&id=7473&Itemid=67 "Scelidosaurus"] at Dinodata