Segnosaurus
Encyclopedia
Segnosaurus is a genus
of herbivorous theropod
dinosaur
belonging to the Therizinosauridae
from the Cretaceous
of Mongolia
.
, Segnosaurus galbinensis, was named and described in 1979 by Dr. Altangerel Perle
. The generic name is derived from Latin
segnis meaning 'slow' or 'sluggish' and Greek
sauros meaning 'lizard', in reference to the stocky build of the hindlimbs. The specific name refers to the Galbin region.
Four specimens were recovered from the Bayan Shireh Formation
of the Mongolian People's Republic
, in sediments dated between the Cenomanian
to Turonian
stages (Late Cretaceous
Period, about 93 million years old). These include the holotype
, IGM 100/80, a partial skeleton consisting of a mandible
, pelvis
, right thighbone, scapulo
coracoid, incomplete forelimb and sacral and caudal vertebrae; and the paratype
s IGM 100/82 and IGM 100/83, both more fragmentary skeletons also lacking the skulls. Later specimen IGM 100/81 was referred, a foot.
estimated the body length at six metres, the weight at 1.3 tonnes. Segnosaurus had an elongated head, large clawed hands, a somewhat elevated torso, a broad strong pelvis, stocky legs and a short tail.
Segnosaurus can be distinguished from all other therizinosaurs on the basis of two unique derived traits (autapomorphies). The in total forty-eight mandibular teeth are markedly peg-like and only slightly recurved: the front or mesial
edge is curved and the back or distal edge is straight. The second autapomorphy is that the claws of the hand are rather flat instead of very narrow. In the same formation the closely related Erlikosaurus
is found; Segnosaurus can be distinguished from this species by its moderate transverse compression of the pedal ungual
s or foot claws. Also the latero
-dorsal
shelf on the dentary, a flat bone surface at the upper outside of the lower jaw, starts at the fourteenth dentary tooth position and runs backwards for half the length of the lower jaw, unlike the shelf in Erlikosaurus, which starts at the fifth tooth position. This would have indicated that Segnosaurus did not have as extensive 'cheek
s' as Erlikosaurus is believed to have had.
was a close relative and the group therefore actually was called the Therizinosauridae
, a name having priority, and that these forms were plant-eaters instead of fish-eaters as had originally been presumed by Perle.
. In this novel, it was portrayed as a burrower.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of herbivorous theropod
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...
belonging to the Therizinosauridae
Therizinosauridae
Therizinosauridae 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:...
from the 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...
of 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...
.
Discovery and naming
In 1973 a Soviet-Mongolian expedition near Amtgay uncovered the fossil of a theropod. In 1974 and 1975 more such remains were discovered, at the same site but also near Khara-Khutul. The type speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, Segnosaurus galbinensis, was named and described in 1979 by Dr. Altangerel Perle
Altangerel Perle
Altangerel Perle is a Mongolian palaeontologist.He is employed at the National University of Mongolia. He has described species such as Goyocephale lattimorei, Achillobator giganticus and Erlikosaurus andrewsi. He has been honored by Polish palaeontologist Halszka Osmólska, who named the species...
. The generic name 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', in reference to the stocky build of the hindlimbs. The specific name refers to the Galbin region.
Four specimens were recovered from the Bayan Shireh Formation
Bayan Shireh Formation
The Bayan Shireh Formation is a geological formation in Burkhant, Mongolia, that dates to the late Cretaceous period...
of the Mongolian People's Republic
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...
, in sediments dated between the Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
to Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
stages (Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
Period, about 93 million years old). These include the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, IGM 100/80, a partial skeleton consisting of a mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
, right thighbone, scapulo
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
coracoid, incomplete forelimb and sacral and caudal vertebrae; and the paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
s IGM 100/82 and IGM 100/83, both more fragmentary skeletons also lacking the skulls. Later specimen IGM 100/81 was referred, a foot.
Description
Segnosaurus was a rather large therizinosaurid. In 2010 Gregory S. PaulGregory 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...
estimated the body length at six metres, the weight at 1.3 tonnes. Segnosaurus had an elongated head, large clawed hands, a somewhat elevated torso, a broad strong pelvis, stocky legs and a short tail.
Segnosaurus can be distinguished from all other therizinosaurs on the basis of two unique derived traits (autapomorphies). The in total forty-eight mandibular teeth are markedly peg-like and only slightly recurved: the front or mesial
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
edge is curved and the back or distal edge is straight. The second autapomorphy is that the claws of the hand are rather flat instead of very narrow. In the same formation the closely related Erlikosaurus
Erlikosaurus
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.-Discovery and naming:The...
is found; Segnosaurus can be distinguished from this species by its moderate transverse compression of the pedal ungual
Ungual
An ungual is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and other ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual phalange.As an adjective, ungual means related to nail, as in periungual .-External...
s or foot claws. Also the latero
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
-dorsal
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
shelf on the dentary, a flat bone surface at the upper outside of the lower jaw, starts at the fourteenth dentary tooth position and runs backwards for half the length of the lower jaw, unlike the shelf in Erlikosaurus, which starts at the fifth tooth position. This would have indicated that Segnosaurus did not have as extensive 'cheek
Cheek
Cheeks constitute the area of the face below the eyes and between the nose and the left or right ear. They may also be referred to as jowls. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve...
s' as Erlikosaurus is believed to have had.
Phylogeny
Perle in 1979 assigned Segnosaurus to the Segnosauridae. He correctly inferred that these were theropods, an opinion not unanimously confirmed by Western scientists until the nineties. At that point it also became clear that TherizinosaurusTherizinosaurus
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 a close relative and the group therefore actually was called the Therizinosauridae
Therizinosauridae
Therizinosauridae 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:...
, a name having priority, and that these forms were plant-eaters instead of fish-eaters as had originally been presumed by Perle.
In popular culture
Segnosaurus was featured in Robert Bakker's novel Raptor RedRaptor Red
Raptor Red is a 1995 American novel by paleontologist Robert T. Bakker. The book is a third-person account of dinosaurs during the Cretaceous Period, told from the point of view of Raptor Red, a female Utahraptor...
. In this novel, it was portrayed as a burrower.