Torosaurus
Encyclopedia
Torosaurus is a genus
of ceratopsid
dinosaur
that lived during the late Cretaceous
period (late Maastrichtian
stage), between 70 and 65 million years ago. It possessed one of the largest skulls of any known land animal. The frilled skull reached 2.6 metres (8.5 ft) in length. From head to tail, Torosaurus is thought to have measured about 9 m (29.5 ft) long and weighed 4 to 6 tonne
s (4.4 to 6.6 ton
s).
In 2010, research on dinosaur ontogeny
(growth and development of individuals over the life span) concluded that Torosaurus may not represent a distinct genus at all, but a mature form of Triceratops
.
, a pair of ceratopsian skulls with elongated frills bearing holes were found in southeastern Wyoming
by John Bell Hatcher
. Paleontologist Othniel Charles Marsh
coined the genus Torosaurus for them. Similar specimens have since been found in Wyoming
, Montana
, South Dakota
, North Dakota
, Utah
and Saskatchewan
. Fragmentary remains that could possibly be identified with the genus have been found in the Big Bend Region of Texas
and in the San Juan Basin of New Mexico
. Paleontologists have observed that Torosaurus specimens are relatively uncommon in the fossil record; specimens of Triceratops are more abundant.
Although the meaning of the name Torosaurus is frequently given as "bull lizard" (from the Latin
taurus "bull"), the name probably means "perforated lizard" (from the Greek
word toreo "pierce, perforate"). The allusion is to the window-like holes, or fenestrae, in the elongated frill, which have traditionally served to distinguish it from the solid frill of Triceratops
. Much of the confusion over etymology of the name results from the fact that Marsh never explicitly explained it in his papers.
Two Torosaurus species have been identified:
Another identification was subsequently regarded as a misassignment:
Torosaurus utahensis was originally described as Arrhinoceratops
utahensis by Gilmore in 1946. Review by Sullivan et al. in 2005 left it as Torosaurus utahensis and somewhat older than T. latus. However, subsequent studies suggested it may well be either Arrhinoceratops or a new genus, as dinosaurs from the northern Hell Creek formation and southern "Alamosaurus
fauna" rarely overlap and were probably separated by a geographic barrier. Research has not yet been published on whether T. utahensis should be regarded as a new genus or, as has been suggested for T. latus, the mature growth stage of a new species of Triceratops.
No juvenile specimens of Torosaurus showing the identifying fenestrae have been found.
Torosaurus has traditionally been classified as part of the subfamily known as Chasmosaurinae
, also known as Ceratopsinae, within the family Ceratopsidae
, within the Ceratopsia
(which name is Ancient Greek for "horned face"), a group of herbivorous dinosaurs with parrot
-like beaks which thrived in North America
and Asia
during the Jurassic
and Cretaceous
Periods. Juvenile individuals have been excavated from a bonebed in the Javelina Formation
of Big Bend National Park
, identified as Torosaurus cf. utahensis based on their proximity to an adult with a characteristic Torosaurus parietal. At least one study has indicated that Torosaurus was most closely related to Triceratops
.
Paleontologists investigating dinosaur ontogeny
(growth and development of individuals over the life span) in the Hell Creek Formation
of Montana
, have hypothesized that Triceratops and Torosaurus may be growth stages in a single genus. John Scannella, in a paper presented in Bristol
, UK at the conference of the Society of Vertebrate Paleontology
(2009 September 25) reclassified the mature Torosaurus specimens as fully mature individuals of Triceratops. Jack Horner
, Scannella's mentor at Montana State University, noted that ceratopsian skulls consist of metaplastic bone. A characteristic of metaplastic bone is that it lengthens and shortens over time, extending and resorbing to form new shapes. Significant variety is seen even in those skulls already identified as Triceratops, Horner observed, "where the horn orientation is backwards in juveniles and forward in adults". Approximately 50% of all subadult Triceratops skulls have two thin areas in the frill that correspond with the placement of "holes" in Torosaurus skulls, suggesting that holes developed to offset the weight that would otherwise have been added as maturing Triceratops individuals grew longer frills. In 2010 Scannella and Horner published their findings after examining the growth patterns in 38 skull specimens (29 of Triceratops, 9 of Torosaurus) from the Hell Creek formation. They concluded that Torosaurus actually represents the mature form of Triceratops.
This conclusion was challenged in 2011 by ceratopsian specialist Andrew Farke. He published a redescription of Nedoceratops hatcheri, a problematic species that at various times has been considered a representative of its own genus, a synonym of a species of Triceratops, a distinct species of Triceratops, or, under the Scannella–Horner hypothesis, an example of an intermediate growth stage between Triceratops and Torosaurus. Farke concluded that Nedoceratops hatcheri is an aged individual of its own genus, closely related to Triceratops. He also regarded the changes required to "age" a Triceratops into a Torosaurus to be without precedent among ceratopsids, requiring addition of epoccipital
s, reversion of bone texture from adult to immature back to adult, and late growth of holes in the frill.
s. During the Cretaceous flowering plants were limited in their geographical distribution. It is likely that ceratopsians fed on the more abundant fern
s, cycad
s and conifers, using their sharp beaks to bite off leaves or needles.
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 ceratopsid
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
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...
that lived during the 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...
period (late Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
stage), between 70 and 65 million years ago. It possessed one of the largest skulls of any known land animal. The frilled skull reached 2.6 metres (8.5 ft) in length. From head to tail, Torosaurus is thought to have measured about 9 m (29.5 ft) long and weighed 4 to 6 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s (4.4 to 6.6 ton
Short ton
The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...
s).
In 2010, research on dinosaur ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
(growth and development of individuals over the life span) concluded that Torosaurus may not represent a distinct genus at all, but a mature form of Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
.
Discoveries and species
In 1891, two years after the naming of TriceratopsTriceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
, a pair of ceratopsian skulls with elongated frills bearing holes were found in southeastern Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
by John Bell Hatcher
John Bell Hatcher
John Bell Hatcher was an American paleontologist and fossil hunter best known for discovering Torosaurus.-Biography:...
. Paleontologist Othniel Charles Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
coined the genus Torosaurus for them. Similar specimens have since been found in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
, Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
and Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
. Fragmentary remains that could possibly be identified with the genus have been found in the Big Bend Region of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
and in the San Juan Basin of New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
. Paleontologists have observed that Torosaurus specimens are relatively uncommon in the fossil record; specimens of Triceratops are more abundant.
Although the meaning of the name Torosaurus is frequently given as "bull lizard" (from the 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...
taurus "bull"), the name probably means "perforated lizard" (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...
word toreo "pierce, perforate"). The allusion is to the window-like holes, or fenestrae, in the elongated frill, which have traditionally served to distinguish it from the solid frill of Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
. Much of the confusion over etymology of the name results from the fact that Marsh never explicitly explained it in his papers.
Two Torosaurus species have been identified:
- T. latus (type speciesType speciesIn 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...
) - T. utahensis
Another identification was subsequently regarded as a misassignment:
- T. gladius (=T. latus)
Torosaurus utahensis was originally described as Arrhinoceratops
Arrhinoceratops
Arrhinoceratops is a genus of ceratopsian dinosaur. The name was coined as its original describer concluded it had no nose-horn, however further analysis revealed this not to be the case...
utahensis by Gilmore in 1946. Review by Sullivan et al. in 2005 left it as Torosaurus utahensis and somewhat older than T. latus. However, subsequent studies suggested it may well be either Arrhinoceratops or a new genus, as dinosaurs from the northern Hell Creek formation and southern "Alamosaurus
Alamosaurus
Alamosaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now North America. It was a large quadrupedal herbivore. Isolated vertebrae and limb bones indicate that it reached sizes comparable to Argentinosaurus and Puertasaurus, which would make it the...
fauna" rarely overlap and were probably separated by a geographic barrier. Research has not yet been published on whether T. utahensis should be regarded as a new genus or, as has been suggested for T. latus, the mature growth stage of a new species of Triceratops.
No juvenile specimens of Torosaurus showing the identifying fenestrae have been found.
Classification and debate
Chasmosaurinae
Chasmosaurinae is a subfamily of ceratopsid dinosaurs. Triceratops is a well-known example. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non-avian dinosaurs, during the K-T extinction...
, also known as Ceratopsinae, within the family Ceratopsidae
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
, within the Ceratopsia
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
(which name is Ancient Greek for "horned face"), a group of herbivorous dinosaurs with parrot
Parrot
Parrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three families: the Psittacidae , the Cacatuidae and the Strigopidae...
-like beaks which thrived in 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...
and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
during the 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...
and 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...
Periods. Juvenile individuals have been excavated from a bonebed in the Javelina Formation
Javelina Formation
The Javelina Formation is a geological formation in Texas. Dating has shown that the strata date to the mid-late Maastrichtian stage of the Late Cretaceous, with the middle part of the formation dated to about 69 million years ago plus or minus 1 Ma and the top situated near the K-Pg boundary,...
of Big Bend National Park
Big Bend National Park
Big Bend National Park is a national park located in the U.S. state of Texas. Big Bend has national significance as the largest protected area of Chihuahuan Desert topography and ecology in the United States, which includes more than 1,200 species of plants, more than 450 species of birds, 56...
, identified as Torosaurus cf. utahensis based on their proximity to an adult with a characteristic Torosaurus parietal. At least one study has indicated that Torosaurus was most closely related to Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
.
Paleontologists investigating dinosaur ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
(growth and development of individuals over the life span) in the Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
of Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, have hypothesized that Triceratops and Torosaurus may be growth stages in a single genus. John Scannella, in a paper presented in Bristol
Bristol
Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...
, UK at the conference of the Society of Vertebrate Paleontology
Society of Vertebrate Paleontology
The Society of Vertebrate Paleontology was founded in 1940 for individuals with an interest in vertebrate paleontology. SVP now has almost 2,000 members. The society's website states that SVP "is organized exclusively for educational and scientific purposes...
(2009 September 25) reclassified the mature Torosaurus specimens as fully mature individuals of Triceratops. Jack Horner
Jack Horner (paleontologist)
John "Jack" R. Horner is an American paleontologist who discovered and named Maiasaura, providing the first clear evidence that some dinosaurs cared for their young. He is one of the best-known paleontologists in the United States...
, Scannella's mentor at Montana State University, noted that ceratopsian skulls consist of metaplastic bone. A characteristic of metaplastic bone is that it lengthens and shortens over time, extending and resorbing to form new shapes. Significant variety is seen even in those skulls already identified as Triceratops, Horner observed, "where the horn orientation is backwards in juveniles and forward in adults". Approximately 50% of all subadult Triceratops skulls have two thin areas in the frill that correspond with the placement of "holes" in Torosaurus skulls, suggesting that holes developed to offset the weight that would otherwise have been added as maturing Triceratops individuals grew longer frills. In 2010 Scannella and Horner published their findings after examining the growth patterns in 38 skull specimens (29 of Triceratops, 9 of Torosaurus) from the Hell Creek formation. They concluded that Torosaurus actually represents the mature form of Triceratops.
This conclusion was challenged in 2011 by ceratopsian specialist Andrew Farke. He published a redescription of Nedoceratops hatcheri, a problematic species that at various times has been considered a representative of its own genus, a synonym of a species of Triceratops, a distinct species of Triceratops, or, under the Scannella–Horner hypothesis, an example of an intermediate growth stage between Triceratops and Torosaurus. Farke concluded that Nedoceratops hatcheri is an aged individual of its own genus, closely related to Triceratops. He also regarded the changes required to "age" a Triceratops into a Torosaurus to be without precedent among ceratopsids, requiring addition of epoccipital
Epoccipital
Epoccipital is an anatomical term for the distinctive bones found lining the frills of ceratopsid dinosaurs. The name is a misnomer, as they are not associated with the occipital bone. Epoccipitals begin as separate bones that fuse during the animal's growth to either the squamosal or parietal...
s, reversion of bone texture from adult to immature back to adult, and late growth of holes in the frill.
Paleobiology
All ceratopsians, including Torosaurus and Triceratops, were herbivoreHerbivore
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. During the Cretaceous flowering plants were limited in their geographical distribution. It is likely that ceratopsians fed on the more abundant fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s and conifers, using their sharp beaks to bite off leaves or needles.
External links
- http://www.dinosaurvalley.com/Visiting_Drumheller/Kids_Zone/Groups_of_Dinosaurs/index.php
- http://www.dinosaurier-web.de/galery/pages_t/torosaurus.html
- http://www.newscientist.com/articleimages/mg20727713.500/1-morphosaurs-how-shapeshifting-dinosaurs-deceived-us.html Chart showing Triceratops/Torosaur growth and development (New Scientist)