Segisaurus

Taxobox
name = "Segisaurus"
fossil_range = Early Jurassic

---

image_width = 250px
image_caption = Reconstruction of "Segisaurus halli", skull is based on "Coelophysis"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
subordo = Theropoda
superfamilia = Coelophysoidea
familia = Coelophysidae
genus = "Segisaurus"
genus_authority = Camp, 1936
subdivision_ranks=Species
subdivision=
*"S. halli" Camp, 1936 (type)

"Segisaurus" (meaning "Segi canyon lizard") is a genus of small coelophysoid theropod dinosaur, that measured approximately 1 metre in length. The only known specimen was discovered in 1933 in early Jurassic strata in Tsegi Canyon, Arizona, for which it was named. "Segisaurus" is the only dinosaur to have ever been excavated from the area. It was later described in 1936 by the paleontologist Charles Lewis Camp. The fragmentary fossil skeleton consisted of portions of the limbs, pelvis, and vertebrae, but no cranial material was located. "Segisaurus" appears to have been closely related to the much more well-known "Coelophysis". One distinction, however, was that "Segisaurus" had solid bones, while those of "Coelophysis"' were hollow. This even made some scientists consider if "Segisaurus" was even a theropod at all. Later investigations into the specimen's pelvic remains in 2005 lead scientists to believe that "Segisaurus" was in fact related more closely to "Procompsognathus".

Description

"Segisaurus" lived about 180 million years ago during the Jurassic period. "Segisaurus" was roughly the size of a goose and was a primitive bipedal theropod. "Segisaurus" was roughly 1 metre long, half a metre tall and weighed about 4-7 kilograms. It was nimble and insectivorous, although it may have scavenged meat also. It was bird-like in structure, with a flexible neck, elongated neck and a stubbish body. "Segisaurus" was three-toed and had powerful legs that were long compared to its body length. Like its legs, "Segisaurus" had a long tail and long forearms. Its collar bone was not unlike a bird's, thus strengthening scientists' arguments that dinosaurs were related to avians.

"Segisaurus" is described from the only specimen ever found. The holotype, however, was a sub-adult, so that the full size of "Segisaurus" as an adult may never be known. Strangely, clavicles were found on the "Segisaurus" specimen, which were unknown in other dinosaurs from that era.

History of discovery

The first discovery of "Segisaurus" was by Max Littlesalt, a Navajo Indian who kept livestock inside Tsegi Canyon. After discovering the remains, Littlesalt pointed out the fossils to archeologists on an expedition inside the canyon. Other than the first finding of "Segisaurus", no other specimens have been discovered. After its initial description by Charles Lewis Camp, the holotype went relatively ignored for the next half century. When the specimen was investigated during this period, all who viewed it commented on the presence of clavicles and the solid bone structures the dinosaur had. According to recent reports, "Segisaurus" is vital in understanding the evolution of early theropods.

When the specimen of "Segisaurus" was discovered, Camp likened it to that of a "sitting hen", due to the position the dinosaur's remains were in. Other theropods used this positions to sleep or stay sheltered during large sand storms, and indeed the "Segisaurus" holotype was found in a bed of sand stone, suggesting that the dinosaur had been submerged in a layer of sand and died. This is still only a hypothesis, as no nest or den materials were discovered along the "Segisaurus" specimen.

In September 2005, the Journal of Vertebrate Paleontology published a report which re-examined the remains of the "Segisaurus" holotype. The authors concluded, that although very unusual, "Segisaurus" was firmly a coelophysoid. They also noted that "Segisaurus" was probably a relative of "Procompsognathus".

References

* Camp, C. (1936). "A new type of small bipedal dinosaur from the Navajo sandstone of Arizona." "Univ. Calif. Publ., Bull. Dept. Geol. Sci.", 24: 39-56.
* Carrano, M.T, Hutchinson, J.R, Sampson, S.D. (2005). "New information on "Segisaurus halli", a small theropod dinosaur from the Early Jurassic of Arizona." "Journal of Vertebrate Paleontology". 25(4): 835-849.

External links

* [http://www.dinoruss.com/de_4/5a64d6a.htm "Segisaurus" in The Dinosaur Encyclopaedia] at Dino Russ's Lair
* [http://www.nhm.ac.uk/jdsml/nature-online/dino-directory/detail.dsml?Genus=Segisaurus "Segisaurus" in the Dino Directory]