Therizinosaur
Encyclopedia
Therizinosaurs are theropod
dinosaur
s belonging to the clade
Therizinosauria. Therizinosaur fossil
s have been found in Early through Late Cretaceous
deposits in Mongolia
, the People's Republic of China
and Western North America
. Various features of the forelimbs, skull and pelvis unite them quite comfortably, both as theropods and, as maniraptora
ns, close relatives to birds.
The name therizinosaur is derived from the Greek
therizo meaning 'to reap' or 'to cut off' and sauros meaning 'lizard'. The older name segnosaur is derived from Latin
segnis meaning 'slow' or 'sluggish' and Greek
sauros meaning 'lizard'.
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 prosauropod dinosaurs. Their unique hip bones, which pointed backwards and were partially fused together, initially reminded paleontologists of the "bird-hipped" ornithischia
ns. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of three feet 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 the prehistoric ground sloth
s.
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. Therizinosaurs spanned a large range of sizes, from the small Beipiaosaurus (which measured 2.2 m, or 7.3 ft in length), to the gigantic Therizinosaurus, which at an approximate 10–12 m (33–40 ft) long and an estimated weight of 6.2 tonnes, was among the largest known theropods
.
Because early finds were incomplete, the strange suite of anatomical features combing 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. 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."
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. 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. 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. Although they are now classified as theropods, therizinosaurs had skulls similar to those of sauropod
s and the shape of their teeth and jaws make it likely that they were herbivore
s.
(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.
Other possible therizinosaurs include Thecocoelurus
, and the Early Jurassic
Eshanosaurus
, which would be the earliest known coelurosaur if it belongs to this group.
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
.
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 Maryanska and Barsbold (2004), Sereno
(2005), Zanno et al. (2009) and Zanno (2010), though other subsequent studies, such as Senter (2007) have continued to use Therizinosauroidea for the therizinosaur "total group".
The following cladogram
follows an analysis by Phil Senter, 2007.
The cladogram below follows the most recent and extensive phylogenetic analysis of Therizinosauria to date, by Lindsay E. Zanno, 2010.
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s belonging to the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Therizinosauria. Therizinosaur fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found in Early through Late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
deposits in Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, the People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
and Western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Various features of the forelimbs, skull and pelvis unite them quite comfortably, both as theropods and, as maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the 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...
ns, close relatives to birds.
The name therizinosaur is derived from the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
therizo meaning 'to reap' or 'to cut off' and sauros meaning 'lizard'. The older name segnosaur is derived from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
segnis meaning 'slow' or 'sluggish' and Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
sauros meaning 'lizard'.
Description
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
ns. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of three feet 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 the prehistoric ground sloth
Ground sloth
Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. Their most recent survivors lived in the Antilles, where it has been proposed they may have survived until 1550 CE; however, the youngest AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP...
s.
Skin impressions from Beipiaosaurus indicate that therizinosaurs were covered with a coat of primitive, down
Down feather
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,...
-like feathers similar to those seen in the compsognathid Sinosauropteryx
Sinosauropteryx
Sinosauropteryx was the first genus of dinosaur outside of Avialae to be found with evidence of feathers. They were covered with "furry" coats of very simple filament-like feathers...
, as well as longer, simpler, quill-like feathers that may have been used in display. Therizinosaurs spanned a large range of sizes, from the small Beipiaosaurus (which measured 2.2 m, or 7.3 ft in length), to the gigantic Therizinosaurus, which at an approximate 10–12 m (33–40 ft) long and an estimated weight of 6.2 tonnes, was among the largest known theropods
Dinosaur size
Size has been one of the most interesting aspects of dinosaur science to the general public. This article lists the largest and smallest dinosaurs from various groups, sorted in order of weight and length....
.
History
Gregory S. Paul
Gregory Scott Paul is a 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...
, 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. It also led Paul to include segnosaurs within paleontologist Robert T. Bakker
Robert T. Bakker
Robert T. Bakker is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic...
'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."
It was not until the mid-1990s, after Alxasaurus
Alxasaurus
Alxasaurus is a genus of therizinosauroid alxasaurid theropod dinosaur from the Early Cretaceous Period of 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...
was discovered and shown to possess more typically theropod features, and Therizinosaurus
Therizinosaurus
Therizinosaurus is a genus of very large theropod dinosaur. Therizinosaurus lived in the late Cretaceous Period , and was one of the last and largest representatives of its unique group, the Therizinosauria...
was recognized as a member of the segnosaur group, that their true identity as herbivorous descendants of the carnivorous theropods became generally accepted. 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
Beipiaosaurus
Beipiaosaurus is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous of China.The exact classification of therizinosaurs had in the past been hotly debated, since their prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical...
in 1999 and Falcarius
Falcarius
Falcarius is a genus of therizinosaurian dinosaur found in east-central Utah, United States. Its name is derived from the word sickle , which scientists have used to describe its unwieldy clawed hands...
in 2005. The scientists who described Falcarius noted that it seemed to represent an intermediate stage between carnivorous and herbivorous theropods, a sort of "missing link
Missing Link
Missing link is a nonscientific term for any transitional fossil, especially one connected with human evolution; see Transitional fossil - Missing links and List of transitonal fossils - Human evolution.Missing Link may refer to:...
" between predatory maniraptorans and plant-eating therizinosaurs. Although they are now classified as theropods, therizinosaurs had skulls similar to those of sauropod
Sauropoda
Sauropoda , or the sauropods , are an infraorder of saurischian dinosaurs. They had long necks, long tails, small heads , and 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...
s and the shape of their teeth and jaws make it likely that they were herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
s.
Taxonomy
Barsbold and Perle named the group Segnosauria as an infraorder of Theropoda in 1980. Dong ZhimingDong Zhiming
Dong Zhiming , from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, is one of China's leading paleontologists. He began working at the IVPP in 1962, learning from Yang Zhongjian who was director at the time...
(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
Therizinosaurus
Therizinosaurus is a genus of very large theropod dinosaur. Therizinosaurus lived in the late Cretaceous Period , and was one of the last and largest representatives of its unique group, the Therizinosauria...
. 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.
- Branch Therizinosauria
- Genus FalcariusFalcariusFalcarius is a genus of therizinosaurian dinosaur found in east-central Utah, United States. Its name is derived from the word sickle , which scientists have used to describe its unwieldy clawed hands...
- Superfamily Therizinosauroidea
- Genus BeipiaosaurusBeipiaosaurusBeipiaosaurus is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous of China.The exact classification of therizinosaurs had in the past been hotly debated, since their prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical...
- Genus EnigmosaurusEnigmosaurusEnigmosaurus is a genus of therizinosauroid theropod dinosaur from the Late Cretaceous of Mongolia, central Asia...
- Genus ErliansaurusErliansaurusErliansaurus is a genus of therizinosauroid theropod dinosaur from the Late Cretaceous of China.A fossil of Erliansaurus was found near Sanhangobi in Inner-Mongolia. The type species, Erliansaurus bellamanus, was described by Xu Xing, Zhang Xiaohong, Paul Sereno, Zhao Xijin, Kuang Xuewen, Han Jun...
- Genus NeimongosaurusNeimongosaurusNeimongosaurus is a genus of herbivorous therizinosaur theropod dinosaur known from the Upper Cretaceous of Nei Mongol, China....
- Genus SuzhousaurusSuzhousaurusSuzhousaurus is a genus of herbivorous therizinosauroid theropod dinosaur from the Early Cretaceous-age Xinminpu Group of the Yujingzi Basin, Gansu, China.-Discovery and naming:...
- Family Alxasauridae
- Family TherizinosauridaeTherizinosauridaeTherizinosauridae is a family of advanced herbivorous or omnivorous theropod dinosaurs. Therizinosaurid fossil remains have been recovered from mid-late Cretaceous Period deposits from Mongolia, China, and the United States.-Classification:...
- Genus Beipiaosaurus
- Genus Falcarius
Other possible therizinosaurs include Thecocoelurus
Thecocoelurus
Thecocoelurus is a genus of theropod dinosaur from the early Cretaceous period of England.Thecocoelurus is known only from half of a single cervical vertebra, discovered by the Rev. William Darwin Fox on the Isle of Wight during the 19th century. After his death the Fox Collection was acquired by...
, and the Early Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
Eshanosaurus
Eshanosaurus
Eshanosaurus is a possible genus of therizinosaurian dinosaur from the early Jurassic Period. It is known only from a partial lower jawbone. The fossil was found in China...
, which would be the earliest known coelurosaur if it belongs to this group.
Phylogeny
The cladeClade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Therizinosauria was first defined by Dale Russell
Dale Russell
Dale A. Russell is a Canadian geologist/palaeontologist, currently Research Professor at The Department of Marine Earth and Atmospheric Sciences of North Carolina State University...
in 1997 as Alxasaurus, Enigmosaurus, Erlikosaurus, Nanshiungosaurus, Segnosaurus, Therizinosaurus, and all taxa closer to them than to oviraptorosaurs, ornithomimids, and troodontids. Paul Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
, in 2005, modified this definition to the most inclusive clade containing Therizinosaurus but not Ornithomimus
Ornithomimus
Ornithomimus is a genus of ornithomimid dinosaur from the Late Cretaceous Period of what is now North America.In 1890 Ornithomimus velox was named by Othniel Charles Marsh on the basis of a foot and partial hand from the Maastrichtian Denver Formation. Another seventeen species have been named since...
, Oviraptor
Oviraptor
Oviraptor is a genus of small Mongolian theropod dinosaur, first discovered by the paleontologist Roy Chapman Andrews, and first described by Henry Fairfield Osborn, in 1924...
, Shuvuuia
Shuvuuia
Shuvuuia is a genus of bird-like theropod dinosaur from the late Cretaceous period of Mongolia. It is a member of the family Alvarezsauridae, small coelurosaurian dinosaurs which are characterized by short but powerful forelimbs specialized for digging. The type species is Shuvuuia deserti, or...
, Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
, or Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
.
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
Falcarius
Falcarius is a genus of therizinosaurian dinosaur found in east-central Utah, United States. Its name is derived from the word sickle , which scientists have used to describe its unwieldy clawed hands...
, and allows the name Therizinosauria to remain in use for the larger group comprising all therizinosaurs. This definition was followed by Maryanska and Barsbold (2004), Sereno
Paul Sereno
Paul Callistus Sereno is an American paleontologist from the University of Chicago who discovered several new dinosaur species on several continents. He has conducted excavations at sites as varied as Inner Mongolia, Argentina, Morocco, and Niger...
(2005), Zanno et al. (2009) and Zanno (2010), though other subsequent studies, such as Senter (2007) have continued to use Therizinosauroidea for the therizinosaur "total group".
The following cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
follows an analysis by Phil Senter, 2007.
The cladogram below follows the most recent and extensive phylogenetic analysis of Therizinosauria to date, by Lindsay E. Zanno, 2010.