Therizinosaur | |
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Reconstructed skeleton of Nothronychus graffami | |
Scientific classification | |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Order: | Saurischia |
Suborder: | Theropoda |
Clade: | Aveairfoila |
Clade: | †Therizinosauria Russell, 1997 |
Synonyms | |
Segnosauria Barsbold, 1980 Contents |
Therizinosaurs (or segnosaurs) were theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China, western North America and possibly Australia [1] . Various features of the forelimbs, skull and pelvis unite these finds as both theropods and as maniraptorans, close relatives to birds.
Theropoda or theropods are a dinosaur suborder that is characterized by hollow bones and three-toed limbs. They are generally classed as a group of saurischian dinosaurs, although a 2017 paper has instead placed them in the proposed clade Ornithoscelida as the closest relatives of the Ornithischia. Theropods were ancestrally carnivorous, although a number of theropod groups evolved to become herbivores, omnivores, piscivores, and insectivores. Theropods first appeared during the Carnian age of the late Triassic period 231.4 million years ago (Ma) and included the sole large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous, about 66 Ma. In the Jurassic, birds evolved from small specialized coelurosaurian theropods, and are today represented by about 10,500 living species.
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago, although the exact origin and timing of the evolution of dinosaurs is the subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago; their dominance continued through the Jurassic and Cretaceous periods. Reverse genetic engineering and the fossil record both demonstrate that birds are modern feathered dinosaurs, having evolved from earlier theropods during the late Jurassic Period. As such, birds were the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event 66 million years ago. Dinosaurs can therefore be divided into avian dinosaurs, or birds; and non-avian dinosaurs, which are all dinosaurs other than birds. This article deals primarily with non-avian dinosaurs.
A clade, also known as monophyletic group, is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life".
The name therizinosaur is derived from the Greek θερίζω [2] therízein, meaning 'to reap' or 'to cut off', and σαῦρος [3] saûros meaning 'lizard'. The older name segnosaur is derived from Latin segnis meaning 'slow' or 'sluggish', and Greek σαυρος, sauros, meaning 'lizard'.
The Ancient Greek language includes the forms of Greek used in Ancient Greece and the ancient world from around the 9th century BCE to the 6th century CE. It is often roughly divided into the Archaic period, Classical period, and Hellenistic period. It is antedated in the second millennium BCE by Mycenaean Greek and succeeded by medieval Greek.
Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, and ultimately from the Phoenician alphabet.
Therizinosaurs had a very distinctive, often confusing set of characteristics. Their long necks, wide torsos, and hind feet with four toes used in walking resembled those of basal sauropodomorph dinosaurs. Their unique hip bones, which pointed backwards and were partially fused together, initially reminded paleontologists of the "bird-hipped" ornithischians. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of around one meter in Therizinosaurus . The unusual range of motion in therizinosaur forelimbs, which allowed them to reach forward to a degree other theropods could not achieve, also supports the idea that they were mainly herbivorous. Therizinosaurs may have used their long reach and strongly curved claws to grasp and shear leafy branches, in a manner similar to large mammals that lived later on, such as chalicotheres, ground sloths, great apes, and giant pandas. [4]
Sauropodomorpha 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 until their decline and extinction at the end of the Cretaceous.
Ornithischia is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure similar to that of birds. The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "of a bird", and ischion (ἴσχιον), plural ischia, meaning "hip joint". However, birds are only distantly related to this group as birds are theropod dinosaurs.
Therizinosaurus is a genus of very large theropod dinosaurs. Therizinosaurus comprises the single species T. cheloniformis, which lived in the late Cretaceous Period, and was one of the last and largest representatives of its unique group, the Therizinosauria. Fossils of this species were first discovered in Mongolia and were originally thought to belong to a turtle-like reptile. It is known only from a few bones, including gigantic hand claws, from which it gets its name.
Skin impressions from Beipiaosaurus indicate that therizinosaurs were covered with a coat of primitive, down-like feathers similar to those seen in the compsognathid Sinosauropteryx , as well as longer, simpler, quill-like feathers that may have been used in display. [5] [6] Therizinosaurs spanned a large range of sizes, from the small Beipiaosaurus (which measured 2.2 m [7 ft 3 in] in length), [7] to the gigantic Therizinosaurus, which at an approximate 10 m (33 ft) long and an estimated weight of 5 tonnes, [8] was among the largest-known theropods.
Beipiaosaurus is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous of China. Before the discovery of Yutyrannus, it was among the largest dinosaurs known from direct evidence to be feathered.
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding (duvets), pillows and sleeping bags. The discovery of feathers trapped in ancient amber suggests that some species of dinosaur may have possessed down-like feathers.
Compsognathidae is a family of coelurosaurian theropod dinosaurs. They were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other dinosaurs such as Archaeopteryx inspired the idea for the connection between dinosaur reptiles and modern-day avian species. Compsognathid fossils preserve diverse integument — skin impressions are known from four genera commonly placed in the group, Compsognathus, Sinosauropteryx, Sinocalliopteryx, and Juravenator. While the latter three show evidence of a covering of some of the earliest primitive feathers over much of the body, Juravenator and Compsognathus also show evidence of scales on the tail or hind legs.
Because early finds were incomplete, the strange suite of anatomical features combining features typical of theropods, prosauropods and ornithischians led some scientists, such as Gregory S. Paul, to conclude that segnosaurs (as they were called before Therizinosaurus was recognized as part of the group) represented a late-surviving suborder of primitive dinosaurs, sometimes thought of as intermediates between prosauropods and ornithischians. Because of their suspected relationship with prosauropods, early depictions of segnosaurs (including illustrations by Paul) portrayed them as semi-quadrupedal, a mode of locomotion now known to have been impossible given the bird-like nature of their wrists. [9] It also led Paul to include segnosaurs within paleontologist Robert T. Bakker's Phytodinosauria in 1986, a superorder which was to include ornithischians, prosauropods, and sauropods, typified by their "blunt, spoon-crowned teeth suitable for cropping plants." [9]
Gregory Scott Paul is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal. Professionally investigating and restoring dinosaurs for three decades, Paul received an on-screen credit as dinosaur specialist on Jurassic Park and Discovery Channel's When Dinosaurs Roamed America and Dinosaur Planet. He is the author and illustrator of Predatory Dinosaurs of the World (1988), The Complete Illustrated Guide to Dinosaur Skeletons (1996), Dinosaurs of the Air (2001), The Princeton Field Guide to Dinosaurs (2010), Gregory S. Paul's Dinosaur Coffee Table Book (2010), and editor of The Scientific American Book of Dinosaurs (2000).
In phylogenetics, a primitive character, trait, or feature of a lineage or taxon is one that is inherited from the common ancestor of a clade and has undergone little change since. Conversely, a trait that appears within the clade group is called advanced or derived. A clade is a group of organisms that consists of a common ancestor and all its lineal descendants.
Robert Thomas Bakker is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic (warm-blooded). Along with his mentor John Ostrom, Bakker was responsible for initiating the ongoing "dinosaur renaissance" in paleontological studies, beginning with Bakker's article "Dinosaur Renaissance" in the April 1975 issue of Scientific American. His special field is the ecological context and behavior of dinosaurs.
It was not until the mid-1990s, after Alxasaurus was discovered and shown to possess more typically theropod features, and Therizinosaurus was recognized as a member of the segnosaur group, that their true identity as herbivorous descendants of the carnivorous theropods became generally accepted. [10] The relation between the more derived therizinosaurids and other theropods was greatly elucidated by the discovery of primitive members of the group, such as Beipiaosaurus in 1999 and Falcarius in 2005. [5] The scientists who described Falcarius noted that it seemed to represent an intermediate stage between carnivorous and herbivorous theropods, a sort of "missing link" between predatory maniraptorans and plant-eating therizinosaurs. [11] Although they are now classified as theropods, therizinosaurs had skulls similar to those of sauropods and the shape of their teeth and jaws make it likely that they were herbivores.
Alxasaurus is a genus of therizinosauroid alxasaurid theropod dinosaur from the Early Cretaceous Period of China in Inner Mongolia. It is one of the earliest known members of the superfamily Therizinosauroidea, but it already possessed the body shape - including the long neck, short tail, and long hand claws - of later therizinosauroids. Like other members of this group, it was a bipedal herbivore with a large gut to process plant material. Several specimens are known and the largest was a little over 3.8 metres long. According to Gregory S. Paul, it was 4 metres long and its weight was about 400 kilograms.
Falcarius is a genus of therizinosaurian dinosaur found in the Cretaceous of east-central Utah, United States. Its name is derived from the word "sickle", falcarius in Latin being a sickle cutter, which scientists have used to describe its large clawed hands.
Sauropoda, or the sauropods, are a clade of saurischian ("lizard-hipped") dinosaurs. They had very long necks, long tails, small heads, and four thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include Brachiosaurus, Diplodocus, Apatosaurus and Brontosaurus.
Barsbold and Perle named the group Segnosauria as an infraorder of Theropoda in 1980. [12] Dong Zhiming (1992) went further, placing the segnosaurs in their own order, Segnosaurischia. This name has been abandoned since the discovery that segnosaurs are a specialized group within the suborder Theropoda. Clark et al. in 2004 considered Segnosaurischia a synonym of Therizinosauroidea.
The superfamily Therizinosauroidea had been established by Maleev in 1954, to include only the bizarre, giant-clawed theropod Therizinosaurus . When it was later realized that Therizinosaurus was an advanced segnosaur, Therizinosauroidea was given a phylogenetic definition to include both groups, and has largely replaced the use of the older name Segnosauria in phylogenetic studies, mainly because of the association of the name Segnosauria with the discredited idea that these animals were relatives of prosauropods.
The following taxonomy follows Zanno, 2010 unless otherwise noted. [13]
The clade Therizinosauria was first defined by Dale Russell in 1997 as Alxasaurus, Enigmosaurus, Erlikosaurus, Nanshiungosaurus, Segnosaurus, Therizinosaurus, and all taxa closer to them than to oviraptorosaurs, ornithomimids, and troodontids. Paul Sereno, in 2005, modified this definition to the most inclusive clade containing Therizinosaurus but not Ornithomimus , Oviraptor , Shuvuuia , Tyrannosaurus , or Troodon . [15]
Therizinosauroidea, previously named as a superfamily with no phylogenetic definition, was first defined by Zhang et al. in 2001, as the clade containing all theropods more closely related to Therizinosaurus than to birds (effectively replacing the older name Segnosauria, which has not yet been defined as a clade). This definition, however, defines the same group as the pre-existing Therizinosauria. An alternate definition was given by Clark in 2004 (as the last common ancestor of Therizinosaurus and Beipiaosaurus and all its descendants), comprising a narrower group that excludes more primitive therizinosaurs, such as Falcarius , and allows the name Therizinosauria to remain in use for the larger group comprising all therizinosaurs. This definition was followed by Teresa Maryańska and Barsbold (2004), Sereno (2005), Zanno et al. (2009) and Zanno (2010), [13] [15] [16] [17] though other subsequent studies, such as Senter (2007, 2012) have continued to use Therizinosauroidea for the therizinosaur "total group". [18]
The following cladogram follows an analysis by Phil Senter, 2007. [18]
Therizinosauroidea |
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The cladogram below follows the extensive phylogenetic analysis of Therizinosauria, by Lindsay E. Zanno, 2010. [13]
Therizinosauria |
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The following cladogram is based on the phylogenetic analysis by Phil Senter et al., 2012. [19]
Therizinosauroidea |
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The cladogram below is the most recent cladogram based on the phylogenetic analysis of Therizinosauria conducted by Hanyong Pu et al., 2013. [20]
Therizinosauria |
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Therizinosauroid behavior is quite poorly understood, but 20th-century studies and subsequent finds have revealed some aspects of their behavior. Nests with sub-spherical eggs have been found, and evidence points to the eggs being buried and abandoned by the parents. And studies of neonates indicate they were well developed and likely precocial—able to leave the nest shortly after birth and suggesting little to no parental care. [21]
CT scans published in 2012 by Stephan Lautenschlager et al. focused on the skull and brain cavity of Erlikosaurus, revealing it to have a large forebrain, and suggesting it had well developed senses of balance, hearing and smell, all of which would have been useful in evading predators, finding food, or in performing complex social behavior. [22]
In 2011, a nesting ground containing 17 clutches of eggs was found in Mongolia's Gobi Desert, with a total of 75 eggs uncovered during excavation. The eggs were 5 inches in diameter and contained no embryos; and there was evidence—in the form of egg shells that had been broken out of—that the young had hatched and left, presumably with their parents. The presence of so many fossilized eggs in one venue implies that therizinosaurs probably were social animals that came together for nesting; and that some genera may have performed parental care. This find, described by Yoshitsugu Kobayashi et al., and mass-death quarries such as those containing Falcarius , augments evidence that therizinosauroids were social, herding animals. Adult therizinosaurs are estimated to have weighed around 500 kg (1,100 lb). [23] [24]
Segnosaurus is a genus of herbivorous theropod dinosaur belonging to the Therizinosauridae from the Cretaceous of Mongolia.
Maniraptora is a clade of coelurosaurian dinosaurs that includes the birds and the non-avian dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea are also often included. Together with the next closest sister group, the Ornithomimosauria, Maniraptora comprises the more inclusive clade Maniraptoriformes. Maniraptorans first appear in the fossil record during the Jurassic Period, and are regarded as surviving today as living birds.
Nothronychus is a genus of theropod dinosaur classified in the group Therizinosauria, from the Cretaceous of North America.
Enigmosaurus is a genus of therizinosauroid theropod dinosaur from the Late Cretaceous of Mongolia, central Asia. It is a herbivorous bipedal dinosaur.
Chilantaisaurus is a genus of theropod dinosaur, possibly a neovenatorid or basal coelurosaur, from the late Cretaceous Ulansuhai Formation of China. The type species, C. tashuikouensis, was described by Hu in 1964. Chilantaisaurus was a large theropod, estimated as weighing between 2.5 metric tons and 4 metric tons. In 2010, Brusatte et al. estimated it to weigh 6,000 kilograms (13,000 lb), based on femur length measurements.
Therizinosauridae is a family of theropod dinosaurs whose fossil remains have been dated to the Mid-to-Late Cretaceous period. Even though representative fossils have only been found throughout China, Mongolia, and the United States, the range of Therizinosauridae was believed to have spanned much of the supercontinent of Laurasia at its height.
Erliansaurus is a genus of therizinosauroid theropod dinosaur from the Late Cretaceous of China.
Erlikosaurus is a genus of herbivorous theropod dinosaur from the late Cretaceous Period, belonging to the Therizinosauridae. Its fossils, a skull and some post-cranial fragments, were found in the Bayan Shireh Formation of Mongolia, dating to around 90 million years ago.
Eshanosaurus is a genus of therizinosaurian dinosaur from the early Jurassic Period. It is known only from a fossil partial lower jawbone, found in China. It may be the earliest known coelurosaur.
Neimongosaurus is a genus of herbivorous therizinosaur theropod dinosaur known from the Upper Cretaceous of Nei Mongol, China.
Nanshiungosaurus is a genus of therizinosaurian theropod dinosaur from the Cretaceous of China.
Saurischia is one of the two basic divisions of dinosaurs. ‘Saurischia’ translates to lizard-hipped. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure, though today most paleontologists classify Saurischia as an unranked clade rather than an order.
Suzhousaurus is a genus of herbivorous therizinosauroid theropod dinosaur from the Early Cretaceous-age Xinminpu Group of the Yujingzi Basin, Gansu, China.
Phytodinosauria is a group of dinosaurs proposed in 1986, combining the Sauropodomorpha and Ornithischia as sister groups, conceptualized as a superorder of herbivorous dinosaurs excluding the carnivorous Theropoda. This hypothesis has been refuted by modern cladistic analysis, showing such a group to be polyphyletic. Modern studies either combine the Theropoda and Sauropodormorpha in the Saurischia or the Theropoda and Ornithischia in the Ornithoscelida.
Martharaptor is an extinct genus of basal therizinosauroid theropod from the Lower Cretaceous of the Cedar Mountain Formation in Utah. It can be distinguished from other therizinosauroids by means of several features of the skeleton which were intermediate between early therizinosauroids such as Falcarius and Beipiaosaurus, and more "advanced" members of the group like therizinosaurids. The deep and homogeneous hand claws clearly differ from the case in early therizinosauroids, but the foot has not yet acquired the robust morphology of therizinosaurids.
This timeline of therizinosaur research is a chronological listing of events in the history of paleontology focused on the therizinosaurs, unusually long-necked, pot-bellied, and large-clawed herbivorous theropod dinosaurs closely related to birds. The early history of therizinosaur research occurred in three phases. The first phase was the discovery of scanty and puzzling fossils in Asia by the Central Asiatic Expeditions of the 1920s and Soviet-backed research in the 1950s. This phase resulted in the discovery of the Therizinosaurus cheloniformis type specimen. Soviet paleontologist Evgeny Maleev interpreted these unusual remains as belonging to some kind of gigantic turtle.