Saurischia

Saurischia (/sɔːˈrɪskiə/ saw-RIS-kee-ə, meaning "reptile-hipped" from the Greek sauros (σαῦρος) meaning 'lizard' and ischion (ἴσχιον) meaning 'hip joint')[1] is one of the two basic divisions of dinosaurs (the other being Ornithischia). ‘Saurischia’ translates to lizard-hipped. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure,[2] though today most paleontologists classify Saurischia as an unranked clade rather than an order.[3]

Saurischians
Temporal range:
Late TriassicPresent, 233.23–0 Ma
Possible Middle Triassic record
Herrerasaurusskeleton
Herrerasaurus (large), Eoraptor (small), and Plateosaurus (skull), three early saurischians
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Seeley, 1888
Subgroups
Alwalkeria
Teyuwasu?
Eusaurischia
Eoraptor
Herrerasauridae
Sauropodomorpha
Theropoda
Aves

Description

All carnivorous dinosaurs (certain types of theropods) are traditionally classified as saurischians, as are all of the birds and one of the two primary lineages of herbivorous dinosaurs, the sauropodomorphs. At the end of the Cretaceous Period, all saurischians except the birds became extinct in the course of the Cretaceous–Paleogene extinction event. Birds, as direct descendants of one group of theropod dinosaurs, are a sub-clade of saurischian dinosaurs in phylogenetic classification.[4]

Saurischian dinosaurs are traditionally distinguished from ornithischian dinosaurs by their three-pronged pelvic structure, with the pubis pointed forward. The ornithischians' pelvis is arranged with the pubis rotated backward, parallel with the ischium, often also with a forward-pointing process, giving a four-pronged structure. The saurischian hip structure led Seeley to name them "lizard-hipped" dinosaurs, because they retained the ancestral hip anatomy also found in modern lizards and other reptiles. He named ornithischians "bird-hipped" dinosaurs because their hip arrangement was superficially similar to that of birds, though he did not propose any specific relationship between ornithischians and birds. However, in the view which has long been held, this "bird-hipped" arrangement evolved several times independently in dinosaurs, first in the ornithischians, then in the lineage of saurischians including birds (Avialae), and lastly in the therizinosaurians. This would then be an example of convergent evolution, avialans, therizinosaurians, and ornithischian dinosaurs all developed a similar hip anatomy independently of each other, possibly as an adaptation to their herbivorous or omnivorous diets.[5]

Classification

Saurischia pelvis

Saurischian pelvis structure (left side)

Tyrannosaurus pelvis left

Tyrannosaurus pelvis (showing saurischian structure – left side)

Ornithischia pelvis

Ornithischian pelvis structure (left side)

Edmontosaurus pelvis left

Edmontosaurus pelvis (showing ornithischian structure – left side)

In his paper naming the two groups, Seeley reviewed previous classification schemes put forth by other paleontologists to divide up the traditional order Dinosauria. He preferred one that had been put forward by Othniel Charles Marsh in 1878, which divided dinosaurs into four orders: Sauropoda, Theropoda, Ornithopoda, and Stegosauria (these names are still used today in much the same way to refer to suborders or clades within Saurischia and Ornithischia).[2]

Seeley, however, wanted to formulate a classification that would take into account a single primary difference between major dinosaurian groups based on a characteristic that also differentiated them from other reptiles. He found this in the configuration of the hip bones, and found that all four of Marsh's orders could be divided neatly into two major groups based on this feature. He placed the Stegosauria and Ornithopoda in the Ornithischia, and the Theropoda and Sauropoda in the Saurischia. Furthermore, Seeley used this major difference in the hip bones, along with many other noted differences between the two groups, to argue that "dinosaurs" were not a natural grouping at all, but rather two distinct orders that had arisen independently from more primitive archosaurs.[2] This concept that "dinosaur" was an outdated term for two distinct orders lasted many decades in the scientific and popular literature, and it was not until the 1960s that scientists began to again consider the possibility that saurischians and ornithischians were more closely related to each other than they were to other archosaurs.

Although his concept of a polyphyletic Dinosauria is no longer accepted by most paleontologists, Seeley's basic division of the two dinosaurian groups has stood the test of time, and has been supported by modern cladistic analysis of relationships among dinosaurs.[6] One alternative hypothesis challenging Seeley's classification was proposed by Robert T. Bakker in his 1986 book The Dinosaur Heresies. Bakker's classification separated the theropods into their own group and placed the two groups of herbivorous dinosaurs (the sauropodomorphs and ornithischians) together in a separate group he named the Phytodinosauria ("plant dinosaurs").[7] The Phytodinosauria hypothesis was based partly on the supposed link between ornithischians and prosauropods, and the idea that the former had evolved directly from the latter, possibly by way of an enigmatic family that seemed to possess characters of both groups, the segnosaurs.[8] However, it was later found that segnosaurs were an unusual type of herbivorous theropod saurischian closely related to birds, and the Phytodinosauria hypothesis fell out of favor.

A 2017 study by Dr Matthew Grant Baron, Dr David B. Norman and Prof. Paul M. Barrett did not find support for a monophyletic Saurischia, according to its traditional definition. Instead, the group was found to be paraphyletic, with Theropoda removed from the group and placed as the sister group to the Ornithischia in the newly defined clade Ornithoscelida. As a result, the authors redefined Saurischia as "the most inclusive clade that contains D. carnegii, but not T. horridus", resulting in a clade containing only the Sauropodomorpha and Herrerasauridae. [9][10]

References

  1. ^ Oxford English Dictionary
  2. ^ a b c Seeley, H.G. (1888). "On the classification of the fossil animals commonly named Dinosauria". Proceedings of the Royal Society of London. 43 (258–265): 165–171. doi:10.1098/rspl.1887.0117.
  3. ^ Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). (2004). The Dinosauria. 2nd edition. University of California Press, Berkeley. 833 pp.
  4. ^ Padian, K. (2004). "Basal Avialae". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka. The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 210–231. ISBN 978-0-520-24209-8.
  5. ^ Zanno, L. E.; Gillette, D. D.; Albright, L. B.; Titus, A. L. (2009). "A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution". Proceedings of the Royal Society B: Biological Sciences. 276 (1672): 3505–11. doi:10.1098/rspb.2009.1029. PMC 2817200. PMID 19605396.
  6. ^ Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). The Dinosauria, Second Edition. University of California Press., 861 pp.
  7. ^ Bakker, R.T. (1986). The Dinosaur Heresies. New York: William Morrow. p. 203. ISBN 0-14-010055-5.
  8. ^ Paul, G.S. (1988). Predatory Dinosaurs of the World, a Complete Illustrated Guide. New York: Simon & Schuster. 464 p.
  9. ^ Baron, M.G., Norman, D.B., and Barrett, P.M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature, 543: 501–506. doi:10.1038/nature21700
  10. ^ https://www.cam.ac.uk/research/news/new-study-shakes-the-roots-of-the-dinosaur-family-tree
Altispinax

Altispinax (; "with high spines") is a genus of large predatory theropod dinosaur from the Early Cretaceous (Valanginian, 140 to 133 million years ago) Wadhurst Clay Formation of East Sussex, England.

Alwalkeria

Alwalkeria (; "for Alick Walker") is a genus of basal saurischian dinosaur from the Late Triassic, living in India. It was a small bipedal omnivore.

Andesaurus

Andesaurus ( AN-də-SOR-əs; "Andes lizard") is a genus of basal titanosaurian sauropod dinosaur which existed during the middle of the Cretaceous Period in South America. Like most sauropods, it would have had a small head on the end of a long neck and an equally long tail. Andesaurus was a very large animal, as were many others of its relatives, which included the largest animals ever to walk the Earth.

Austrosaurus

Austrosaurus (meaning "Southern lizard") was an extinct genus of sauropod dinosaur from the Allaru Formation and Winton Formation, from the early Cretaceous (110-105 million years ago) of Central-Western Queensland in Australia.

Como Bluff

Como Bluff is a long ridge extending east-west, located between the towns of Rock River and Medicine Bow, Wyoming. The ridge is an anticline, formed as a result of compressional geological folding. Three geological formations, the Sundance, the Morrison, and the Cloverly Formations, containing fossil remains from the Late Jurassic of the Mesozoic Era are exposed. Nineteenth century paleontologists discovered many well-preserved specimens of dinosaurs, as well as mammals, turtles, crocodilians, and fish from the Morrison Formation. Because of this, Como Bluff is considered to be one of the major sites for the early discovery of dinosaur remains. Among the species discovered is the only known specimen of Coelurus. Significant discoveries were made in 22 different areas scattered along the entire length of the ridge. It is included on the National Register of Historic Places as well as the National Natural Landmark list.

Dinosaur classification

Dinosaur classification began in 1842 when Sir Richard Owen placed Iguanodon, Megalosaurus, and Hylaeosaurus in "a distinct tribe or suborder of Saurian Reptiles, for which I would propose the name of Dinosauria." In 1887 and 1888 Harry Seeley divided dinosaurs into the two orders Saurischia and Ornithischia, based on their hip structure. These divisions have proved remarkably enduring, even through several seismic changes in the taxonomy of dinosaurs.

The largest change was prompted by entomologist Willi Hennig's work in the 1950s, which evolved into modern cladistics. For specimens known only from fossils, the rigorous analysis of characters to determine evolutionary relationships between different groups of animals (clades) proved incredibly useful. When computer-based analysis using cladistics came into its own in the 1990s, paleontologists became among the first zoologists to almost wholeheartedly adopt the system. Progressive scrutiny and work upon dinosaurian interrelationships, with the aid of new discoveries that have shed light on previously uncertain relationships between taxa, have begun to yield a stabilizing classification since the mid-2000s. While cladistics is the predominant classificatory system among paleontology professionals, the Linnean system is still in use, especially in works intended for popular distribution.

Dinosaurs of the Isle of Wight

The Isle of Wight is one of the richest dinosaur localities in Europe, with over 20 species of dinosaur having been recognised from the early Cretaceous Period (in particular between 132 and 110 million years ago), some of which were first identified on the island, as well as the contemporary non-dinosaurian species of crocodile, turtle and pterosaur.

Compton Bay, near Freshwater features dinosaur footprints which are visible at low tide.

Euskelosaurus

Euskelosaurus browni ("good leg lizard") is a semi-bipedal plateosaurid sauropodomorph dinosaur from the early Triassic of South Africa and Lesotho. Fossils have only been recovered from the lower Elliot Formation in South Africa and Lesotho, and in one locality in Zimbabwe.

Evolution of dinosaurs

This article gives an outline and examples of dinosaur evolution. For a detailed list of interrelationships see Dinosaur classification.

Dinosaurs evolved within a single lineage of archosaurs 243-233 Ma (million years ago) from the Anisian to the Carnian ages, the latter part of the middle Triassic. Dinosauria is a well-supported clade, present in 98% of bootstraps. It is diagnosed by many features including loss of the postfrontal on the skull and an elongate deltopectoral crest on the humerus.In March 2017, scientists reported a new way of classifying the dinosaur family tree, based on newer and more evidence than available earlier. According to the new classification, the original dinosaurs, arising 200 million years ago, were small, two-footed omnivorous animals with large grasping hands. Descendants (for the non-avian dinosaurs) lasted until 66 million years ago.

Ferganasaurus

Ferganasaurus was a genus of dinosaur first formally described in 2003 by Alifanov and Averianov. The type species is Ferganasaurus verzilini. It was a sauropod similar to Rhoetosaurus. The fossils were discovered in 1966 in Kyrgyzstan from the Balabansai Formation and date to the Callovian stage of the Middle Jurassic.

Garden Park, Colorado

Garden Park is a paleontological site in Fremont County, Colorado, known for its Jurassic dinosaurs and the role the specimens played in the infamous Bone Wars of the late 19th century. Located 10 km (6.2 mi) north of Cañon City, the name originates from the area providing vegetables to the miners at nearby Cripple Creek in the 19th century. Garden Park proper is a triangular valley surrounded by cliffs on the southeast and southwest and by mountains to the north; however, the name is also refers to the dinosaur sites on top and along the cliffs. The dinosaur sites now form the Garden Park Paleontological Resource Area, which is overseen by the Bureau of Land Management.

Guaibasauridae

Guaibasauridae is a family of basal saurischian dinosaurs, known from fossil remains of late Triassic period formations in Brazil and Argentina.

Herrerasauridae

Herrerasauridae is a family of carnivorous basal saurischian dinosaurs. They are among the oldest known dinosaurs, first appearing in the fossil record around 233.23 million years ago (Late Triassic), before becoming extinct by the end of the Triassic period. Herrerasaurids were relatively small-sized dinosaurs, normally not more than 4 metres (13 ft) long. The best known representatives of this group are from South America (Brazil, Argentina), where they were first discovered in the 1960s. A nearly complete skeleton of Herrerasaurus ischigulastensis was discovered in the Ischigualasto Formation in San Juan, Argentina, in 1988. Less complete herrerasaurids have been found in North America, and they may have inhabited other continents as well.

Herrerasaurid anatomy is unusual and specialized, and they are not considered to be ancestral to any later dinosaur group. They only superficially resemble theropods and often present a mixture of very primitive and derived traits. The acetabulum is only partly open, and there are only two sacral vertebrae, the lowest number among dinosaurs. The pubic bone has a derived structure, being rotated somewhat posteriorly and folded to create a superficially tetanuran-like terminal expansion, especially prominent in H. ischigulastensis. The hand is primitive in having five metacarpals and the third finger longer than the second, but resembles those of theropods in having only three long fingers, with curved claws. Herrerasaurids also have a hinged mandible, which is also found in theropods.

Ornithoscelida

Ornithoscelida is a clade that includes various major groupings of dinosaurs. An order Ornithoscelida was originally proposed by Thomas Henry Huxley but later abandoned in favor of Harry Govier Seeley's division of Dinosauria into Saurischia and Ornithischia. The term was revived in 2017 after a new cladistic analysis by Baron et al.

Panphagia

Panphagia is a genus of sauropodomorph dinosaur described in 2009. It lived around 231 million years ago, during the Carnian age of the Late Triassic period in what is now northwestern Argentina. Fossils of the genus were found in the La Peña Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin. The name Panphagia comes from the Greek words pan, meaning "all", and phagein, meaning "to eat", in reference to its inferred omnivorous diet. Panphagia is one of the earliest known dinosaurs, and is an important find which may mark the transition of diet in early sauropodomorph dinosaurs.

Saturnaliinae

Saturnaliinae is a clade of sauropodomorph dinosaurs found in Brazil and Zimbabwe.

In 2010, Martin Ezcurra defined the subfamily Saturnaliinae for the clade containing Saturnalia and Chromogisaurus, which were found to be close relatives in several studies. While they are sometimes found to be a subgroup within the Guaibasauridae, other studies have found the saturnaliines to form an independent lineage at the very base of the sauropodomorph family tree. Langer and colleagues (2019) recovered Pampadromaeus and Panphagia as relatives of Saturnalia and Chromogisaurus, elevating Saturnaliinae to family rank as Saturnaliidae. They recovered Guaibasaurus as a basal theropod.

Sauropodomorpha

Sauropodomorpha ( SOR-ə-POD-ə-MOR-fə; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The "prosauropods", which preceded the sauropods, were smaller and were often able to walk on two legs. The sauropodomorphs were the dominant terrestrial herbivores throughout much of the Mesozoic Era, from their origins in the mid-Triassic (approximately 230 Ma) until their decline and extinction at the end of the Cretaceous (approximately 66 Ma).

Tambatitanis

Tambatitanis is an extinct genus of titanosauriform dinosaur from the Early Cretaceous (probably early Albian) of Japan. It is known from a single type species, Tambatitanis amicitiae. It was probably around 14 meters long and its mass was estimated at some 4 tonnes. It was a basal titanosauriform and possibly belonged to the Euhelopodidae.

Vulcanodontidae

The Early Jurassic sauropod dinosaurs Zizhongosaurus, Barapasaurus, Tazoudasaurus, and Vulcanodon may form a natural group of basal sauropods called the Vulcanodontidae. Basal vulcanodonts include some of the earliest known examples of sauropods. The family-level name Vulcanodontidae was erected by M.R. Cooper in 1984. In 1995 Hunt et al. published the opinion that the family is synonymous with the Barapasauridae. One of the key morphological features specific to the family is an unusually narrow sacrum.

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