Segisaurus

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Segisaurus
Temporal range: Early Jurassic
Segisaurus halli.jpg
Restoration of the holotype skeleton from 1936
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: Coelophysidae
Genus: Segisaurus
Camp, 1936
Type species
Segisaurus halli
Camp, 1936

Segisaurus (meaning "Segi canyon lizard") is a genus of small coelophysid theropod dinosaur, that measured approximately 1 metre (3.3 feet) in length. The only known specimen was discovered 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.

Contents

Description

Restoration Segisaurus.jpg
Restoration

Segisaurus lived sometime between ~200 and 195 million years ago during the Jurassic period. [1] It was a primitive bipedal theropod roughly around the size of a goose. Segisaurus was 1 meter (3.3 feet) long, half a meter (1.65 feet) 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, elongated neck and stout 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 furcula 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 UCMP 32101, which was a sub-adult. The full size of Segisaurus as an adult may never be known. Furcula were found in the Segisaurus specimen, making it one of the first known non-avian dinosaurs to preserve furcula found. [2] These furculae were initially thought to be clavicles, which led Charles Lewis Camp to speculate that the "splint-like" neck ribs supported a Draco -like patagium along the neck, to improve the animal's ability to move quickly. [3] Segisaurus is significant because it demonstrates that the clavicle was primitively present in early theropods. [4]

Classification

Size comparison Segisaurus Scale.svg
Size comparison

Segisaurus was described in 1936 by the paleontologist Charles Lewis Camp, based on specimen UCMP 32101, a fragmentary fossil skeleton which consisted of portions of the limbs, pelvis, and vertebrae. Cranial material was not recovered. Segisaurus went relatively ignored for the next half century. When the specimen was examined during this period, all who viewed it commented on the supposed presence of clavicles and the apparently "solid" bones that the dinosaur had. Segisaurus appeared to be closely related to the better-known Coelophysis , but unlike the hollow bones of Coelophysis, Segisaurus had solid bones. This caused some scientists question whether Segisaurus was a theropod at all. In 2005, a re-examination of the Segisaurus holotype revealed that contrary to reports it did in fact have hollow bones and that the clavicles were instead fragmented furculae. [2] In this study, Carano et al. found that although it was very unusual, Segisaurus was firmly a coelophysoid, and probably a close relative of Procompsognathus . [2]

Distinguishing anatomical features

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group.

According to Rauhut (2003), Segisaurus can be distinguished based on the following features: [5]

History of discovery

Illustration of the holotype skeleton, shown as it was found Segisaurus halli holotype.jpg
Illustration of the holotype skeleton, shown as it was found

In 1933, Max Littlesalt, a Navajo Indian, discovered the holotype in Tsegi Canyon of the Navajo Sandstone of Coconino County, Arizona. The specimen was found in calcareous sandstone, which was deposited during the Pliensbachian - Toarcian stages of the Jurassic, approximately 190 to 174 million years ago. After discovering the remains, Littlesalt, who kept livestock inside the canyon, pointed out the fossils to archeologists who were on an expedition inside the canyon. Other than the first finding of Segisaurus, no other specimens have been discovered.

When the specimen of Segisaurus was discovered, Camp likened its posture to that of a "sitting hen", due to the position the dinosaur's remains were in. [3] Other theropods used this positions to sleep or stay sheltered during sand and ash storms.

Taphonomy

The Segisaurus holotype was found in a bed of sandstone, suggesting that the dinosaur had been buried in a layer of sand and died. This is still only a hypothesis, as no nest or den materials were discovered with the specimen. Geological features of the Navajo Sandstone Formation suggest that this genus lived in an environment resembling modern sand dunes.

Related Research Articles

<i>Dilophosaurus</i> Genus of theropod dinosaur from Early Jurassic

Dilophosaurus is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 186 million years ago. Three skeletons were discovered in northern Arizona in 1940, and the two best preserved were collected in 1942. The most complete specimen became the holotype of a new species in the genus Megalosaurus, named M. wetherilli by Samuel P. Welles in 1954. Welles found a larger skeleton belonging to the same species in 1964. Realizing it bore crests on its skull, he assigned the species to the new genus Dilophosaurus in 1970, as Dilophosaurus wetherilli. The genus name means "two-crested lizard", and the species name honors John Wetherill, a Navajo councilor. Further specimens have since been found, including an infant. Fossil footprints have also been attributed to the animal, including resting traces. Another species, Dilophosaurus sinensis from China, was named in 1993, but was later found to belong to the genus Sinosaurus.

<i>Coelophysis</i> Genus of theropod dinosaurs from the late Triassic

Coelophysis is a genus of coelophysid theropod dinosaur that lived approximately 215 to 208.5 million years ago during the Late Triassic period from the middle to late Norian age in what is now the southwestern United States. Megapnosaurus was once considered to be a species within this genus, but this interpretation has been challenged since 2017 and the genus Megapnosaurus is now considered valid.

<span class="mw-page-title-main">Coelophysoidea</span> Extinct superfamily of dinosaurs

Coelophysoidea is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly classified, and some species had delicate cranial crests. Sizes range from about 1 to 6 m in length. It is unknown what kind of external covering coelophysoids had, and various artists have portrayed them as either scaly or feathered. Some species may have lived in packs, as inferred from sites where numerous individuals have been found together.

<i>Procompsognathus</i> Extinct genus of dinosaurs

Procompsognathus is an extinct genus of coelophysid theropod dinosaur that lived approximately 210 million years ago during the later part of the Triassic Period, in what is now Germany. Procompsognathus was a small-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 1 m (3.3 ft) long.

<i>Saltriovenator</i> Extinct genus of dinosaurs

Saltriovenator is a genus of ceratosaurian dinosaur that lived during the Sinemurian stage of the Early Jurassic in what is now Italy. The type and only species is Saltriovenator zanellai; in the past, the species had been known under the informal name "saltriosaur". Although a full skeleton has not yet been discovered, Saltriovenator is thought to have been a large, bipedal carnivore similar to Ceratosaurus.

<span class="mw-page-title-main">Allosauridae</span> Extinct family of theropod dinosaurs

Allosauridae is a family of medium to large bipedal, carnivorous allosauroid theropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles Marsh in 1878. Allosaurids are characterized by an astragalus with a restriction of the ascending process to the lateral part of the bone, a larger medial than lateral condyle, and a horizontal groove across the face of the condyles.

<i>Liliensternus</i> Extinct genus of dinosaurs

Liliensternus is an extinct genus of basal neotheropod dinosaur that lived approximately 210 million years ago during the latter part of the Triassic Period in what is now Germany. Liliensternus was a moderate-sized, bipedal, ground-dwelling carnivore, that could grow up to 5.15 m (16.9 ft) long. It is the best represented Triassic theropod from Europe and one of the largest known.

<i>Gojirasaurus</i> Extinct genus of dinosaurs

Gojirasaurus is a potentially dubious genus of coelophysoid theropod dinosaur named after the giant monster movie character Godzilla.

Podokesaurus is a genus of coelophysoid dinosaur that lived in what is now the eastern United States during the Early Jurassic Period. The first fossil was discovered by the geologist Mignon Talbot near Mount Holyoke, Massachusetts, in 1910. The specimen was fragmentary, preserving much of the body, limbs, and tail. In 1911, Talbot described and named the new genus and species Podokesaurus holyokensis based on it. The full name can be translated as "swift-footed lizard of Holyoke". This discovery made Talbot the first woman to find and describe a non-bird dinosaur. The holotype fossil was recognized as significant and was studied by other researchers, but was lost when the building it was kept in burned down in 1917; no unequivocal Podokesaurus specimens have since been discovered. It was made state dinosaur of Massachusetts in 2022.

<i>Sinosaurus</i> Genus of dinosaurs

Sinosaurus is an extinct genus of theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately 5.5 metres (18 ft) in length and 300 kilograms (660 lb) in body mass. Fossils of the animal were found at the Lufeng Formation, in the Yunnan Province of China.

<i>Zupaysaurus</i> Extinct genus of dinosaurs

Zupaysaurus is an extinct genus of early theropod dinosaur living during the Norian stage of the Late Triassic in what is now Argentina. Fossils of the dinosaur were found in the Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. Although a full skeleton has not yet been discovered, Zupaysaurus can be considered a bipedal predator, up to 4 metres (13 ft) long. It may have had two parallel crests running the length of its snout.

<i>Camposaurus</i> Extinct genus of dinosaurs

Camposaurus is a coelophysid dinosaur genus from the Norian stage of the Late Triassic period of North America. The pertinent fossil remains date back to the early to middle Norian stage, and is widely regarded as the oldest known neotheropod.

Chuandongocoelurus is a genus of carnivorous tetanuran theropod dinosaur from the Jurassic of China.

Lophostropheus is an extinct genus of coelophysoid theropod dinosaur that lived approximately 205.6 to 196.5 million years ago during the boundary between the Late Triassic Period and the Early Jurassic Period, in what is now Normandy, France. Lophostropheus is one of the few dinosaurs that may have survived the Triassic–Jurassic extinction event.

Kayentavenator is a genus of small carnivorous tetanuran dinosaur that lived during the Early Jurassic Period; fossils were recovered from the Kayenta Formation of northeastern Arizona and were described in 2010.

<i>Sarahsaurus</i> Extinct genus of dinosaurs

Sarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic period in what is now northeastern Arizona, United States.

<i>Megapnosaurus</i> Extinct genus of dinosaur

Megapnosaurus is an extinct genus of coelophysid theropod dinosaur that lived approximately 188 million years ago during the early part of the Jurassic Period in what is now Africa. The species was a small to medium-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 2.2 m (7.2 ft) long and weigh up to 13 kg (29 lb).

<i>Coelophysis</i>? <i>kayentakatae</i> Extinct species of dinosaur

Coelophysis? kayentakatae is an extinct species of neotheropod dinosaur that lived approximately 200–196 million years ago during the early part of the Jurassic Period in what is now the southwestern United States. It was originally named Syntarsus kayentakatae, but the genus Syntarsus was found to be preoccupied by a Colydiine beetle, so it was moved to the genus Megapnosaurus, and then to Coelophysis. A recent reassessment suggests that this species may require a new genus name.

<i>Tachiraptor</i> Extinct genus of dinosaurs

Tachiraptor is a genus of carnivorous theropod dinosaurs found in the early Jurassic period La Quinta Formation of Venezuela. It includes one species, Tachiraptor admirabilis, described from a fossilized tibia and ischium. They were small bipedal dinosaurs, with a deduced total body length of just over 1.5 m (4.9 ft). They were likely generalist predators, preying on smaller vertebrates like other dinosaurs or lizards.

<i>Dracoraptor</i> Genus of reptiles (fossil)

Dracoraptor is a genus of coelophysoid dinosaur that lived during the Hettangian stage of the Early Jurassic Period of what is now Wales dated at 201.3 ± 0.2 million years old.

References

  1. Judith Totman Parrish, E. Troy Rasbury, Marjorie A. Chan & Stephen T. Hasiotis (2019) Earliest Jurassic U-Pb ages from carbonate deposits in the Navajo Sandstone, southeastern Utah, USA. Geology 47(11): 1015-1019.
  2. 1 2 3 4 Carrano, M.T, Hutchinson, J.R, and 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.
  3. 1 2 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.
  4. Chure, D. J., and Madsen, J. H., 1996, The furcula in Allosaurid Theropods and its implication for determining bird origins: Journal of Vertebrate Paleontology, v. 16, supplement to n. 3, Abstracts of Papers, Fifty-sixth Annual Meeting, Society of Vertebrate Paleontology, American Museum of Natural History, New York, New York, October 16–19, p. 28A.
  5. Rauhut, O. W. M., 2003, The interrelationships and evolution of basal theropod dinosaurs: Special Papers in Palaeontology, v. 69, p. 1-213.