Segisaurus Temporal range: Early Jurassic, | |
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Restoration of the holotype skeleton from 1936 | |
Scientific classification | |
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.
Segisaurus lived about 183 million years ago during the Jurassic period. 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. [1] 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. [2] Segisaurus is significant because it demonstrates that the clavicle was primitively present in early theropods. [3]
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. [1] 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 . [1]
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: [4]
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. [2] Other theropods used this positions to sleep or stay sheltered during sand and ash storms.
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.
Dilophosaurus is a genus of theropod dinosaurs that lived in what is now North America during the Early Jurassic, about 193 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. 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.
Coelophysis is an extinct genus of coelophysid theropod dinosaur that lived approximately 228 to 200 million years ago during the latter part of the Triassic Period from the Carnian and Rhaetian faunal stages in what is now the southwestern United States; a specimen possibly belonging to the second species, C. rhodesiensis, has been found in South Africa and Zimbabwe, though this interpretation has been challenged since 2017.
Coelophysoidea were common dinosaurs of 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.
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.
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.
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.
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.
Gojirasaurus is a dubious genus of coelophysoid theropod dinosaur named after the giant monster movie character Gojira.
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 nominated as state dinosaur of Massachusetts in 2021.
Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of Coelophysidae are characterized by long, slender skulls and light skeletons built for speed. One member, Coelophysis, displays the earliest known furcula in a dinosaur.
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.
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.
Aniksosaurus is a genus of dinosaur from what is now Chubut Province, Argentina. It was a theropod, specifically a coelurosaur, which lived in the Cenomanian to Turonian of the Cretaceous period, between 96-91 million years ago. The type species, Aniksosaurus darwini, was formally described from the Bajo Barreal Formation of the Golfo San Jorge Basin by Rubén Dario Martínez and Fernando Emilio Novas in 2006; the name was first coined in 1995 and reported in the literature in 1997. The specific epithet honors Charles Darwin who visited Patagonia in 1832/1833 during the Voyage of the Beagle.
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.
Sarahsaurus is a genus of basal sauropodomorph dinosaur which lived during the Early Jurassic period in what is now northeastern Arizona, United States.
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). It was originally given the genus name Syntarsus, but that name was later determined to be preoccupied by a beetle. The species was subsequently given a new genus name, Megapnosaurus, by Ivie, Ślipiński & Węgrzynowicz in 2001. Many subsequent studies have classified it as a species within the genus Coelophysis, but this interpretation has been challenged by more subsequent studies.
Coelophysis? kayentakatae is an extinct species of coelophysid 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. While originally assigned to the genus Syntarsus as Syntarsus kayentakatae, that genus name was found to be preoccupied by a Colydiine beetle, so it was moved to the genus Megapnosaurus as Megapnosaurus kayentakatae. Later it was moved again to Coelophysis, however the species still possesses no definite genus assignment.
Dracoraptor is a genus of coelophysoid dinosaur that lived during the Hettangian stage of the Early Jurassic Period of what is now Wales, sometime between 201 to 199 million years ago. It was discovered in 2014 at the Blue Lias Formation of the United Kingdom, and named in 2016 by British palaeontologist David Martill and colleagues, with the type species being Dracoraptor hanigani.