Tyrannosauroidea
Encyclopedia
Tyrannosauroidea is a superfamily
(or clade
) of coelurosaurian theropod dinosaur
s that includes the family
Tyrannosauridae
as well as more basal
relatives. Tyrannosauroids lived on the Laurasia
n supercontinent
beginning in the Jurassic
Period. By the end of the Cretaceous Period, tyrannosauroids were the dominant large predators in the Northern Hemisphere
, culminating in the gigantic Tyrannosaurus
itself. Fossil
s of tyrannosauroids have been recovered on what are now the continents of North America
, Europe
, Asia
, and possibly Australia
.
Tyrannosauroids were biped
al carnivore
s, as were most theropods, and were characterized by numerous skeletal features
, especially of the skull
and pelvis
. Early in their existence, tyrannosauroids were small predators with long, three-fingered forelimbs. Late Cretaceous
genera became much larger, including some of the largest land-based predators ever to exist, but most of these later genera had proportionately small forelimbs with only two digits. Primitive feather
s have been found on Dilong
, an early tyrannosauroid from China
, and may have been present in other tyrannosauroid genera as well. Prominent bony crests in a variety of shapes and sizes on the skulls of many tyrannosauroids may have served display
functions.
measured 3 meters (10 ft long). Teeth from lower Lower Cretaceous rocks (140 to 136 million years old) of Hyogo, Japan
, appear to have come from an approximately 5 metres (16.4 ft) long animal, possibly indicating an early size increase in the lineage. An immature Eotyrannus
was over 4 meters (13 ft) in length, and a subadult Appalachiosaurus
was estimated at more than 6 meters (20 ft) long, indicating that both genera reached larger sizes. The Late Cretaceous tyrannosaurids ranged from the 9 meter (30 ft) Albertosaurus
and Gorgosaurus
to Tyrannosaurus, which exceeded 12 meters (40 ft) in length and may have weighed more than 6400 kilogram
s (7 short ton
s). A 2010 review of the literature concluded that tyrannosaurs were "small- to mid-sized" for their first 80 million years but were "some of the largest terrestrial carnivores to ever live" in their last 20 million years.
Skulls of early tyrannosauroids were long, low and lightly constructed, similar to other coelurosaurs, while later forms had taller and more massive skulls. Despite the differences in form, certain skull features are found in all known tyrannosauroids. The premaxilla
ry bone is very tall, blunting the front of the snout, a feature which evolved convergently
in abelisaurids. The nasal bone
s are characteristically fused together, arched slightly upwards and often very roughly textured on their upper surface. The premaxillary teeth at the front of the upper jaw are shaped differently than the rest of the teeth, smaller in size and with a D-shaped cross section
. In the lower jaw
, a prominent ridge on the surangular bone
extends sideways from just below the jaw joint, except in the basal Guanlong.
Tyrannosauroids had S-shaped necks and long tails, as did most other theropods. Early genera had long forelimbs, about 60% the length of the hindlimb in Guanlong, with the typical three digits of coelurosaurs. The long forelimb persisted at least through the Early Cretaceous Eotyrannus, but is unknown in Appalachiosaurus. Derived
tyrannosaurids have forelimbs strongly reduced in size, the most extreme example being Tarbosaurus
from Mongolia
, where the humerus
was only one-quarter the length of the femur
. The third digit of the forelimb was also reduced over time. This digit was unreduced in the basal Guanlong, but in Dilong it was significantly more slender than the other two digits. Eotyrannus still had three functional digits on each hand, but tyrannosaurids had only two, although the vestigial remnants of the third are found on some specimens. As in most coelurosaurs, the second digit of the hand is the largest, even when the third digit is not present.
Characteristic features of the tyrannosauroid pelvis include a concave notch at the upper front end of the ilium
, a sharply defined vertical ridge on the outside surface of the ilium, extending upwards from the acetabulum
(hip socket), and a huge "boot" on the end of the pubis
, more than half as long as the shaft of the pubis itself. These features are found in all known tyrannosauroids, including basal members Guanlong and Dilong. The pubis is not known in Aviatyrannis
or Stokesosaurus
but both show typical tyrannosauroid characters in the ilium. The hindlimbs of all tyrannosauroids, like most theropods, had four toes, although the first toe (the hallux
) did not contact the ground. Tyrannosauroid hindlimbs are longer relative to body size than almost any other theropods, and show proportions characteristic of fast-running
animals, including elongated tibia
e and metatarsals. These proportions persist even in the largest adult Tyrannosaurus, despite its probable inability to run. The third metatarsal of tyrannosaurids was pinched at the top between the second and fourth, forming a structure known as the arctometatarsus. The arctometatarsus was also present in Appalachiosaurus but it is unclear whether it was found in Eotyrannus or Dryptosaurus
. This structure was shared by derived ornithomimids, troodontids and caenagnathids, but was not present in basal tyrannosauroids like Dilong
, indicating convergent evolution
.
in 1905, along with the family Tyrannosauridae. The name is derived from the Ancient Greek
words τυραννος/tyrannos ('tyrant') and σαυρος/sauros ('lizard'). The superfamily name Tyrannosauroidea was first published in a 1964 paper by British
paleontologist Alick Walker
. The suffix
-oidea, commonly used in the name of animal superfamilies, is derived from the Greek ειδος/eidos ('form').
Scientists have commonly understood Tyrannosauroidea to include the tyrannosaurids and their immediate ancestors. With the advent of phylogenetic taxonomy in vertebrate paleontology, however, the clade
has received several more explicit definitions. The first was by Paul Sereno
in 1998, where Tyrannosauroidea was defined as a stem-based taxon
including all species sharing a more recent common ancestor with Tyrannosaurus rex than with neornithean birds. To make the family more exclusive, Thomas Holtz redefined it in 2004 to include all species more closely related to Tyrannosaurus rex than to Ornithomimus velox, Deinonychus antirrhopus or Allosaurus fragilis. Sereno published a new definition in 2005, using Ornithomimus edmontonicus, Velociraptor mongoliensis and Troodon formosus as external specifiers. The Sereno definition was adopted in a 2010 review.
Superfamily Tyrannosauroidea
, which included almost all large theropods. Within this group, the allosaurid
s were often considered to be ancestral to tyrannosaurids. In the early 1990s, cladistic analyses instead began to place tyrannosaurids into the Coelurosauria, echoing suggestions first published in the 1920s. Tyrannosaurids are now universally considered to be large coelurosaurs.
Holtz 2004
Carr
et al. 2005
Xu et al. 2006
Brusatte et al. 2010
In 1994, Holtz grouped tyrannosauroids with elmisaurids, ornithomimosaurs and troodonts into a coelurosaurian clade called Arctometatarsalia based on a common ankle structure where the second and fourth metatarsals meet near the tarsal
bones, covering the third metatarsal when viewed from the front. Basal tyrannosauroids like Dilong, however, were found with non-arctometatarsalian
ankles, indicating that this feature evolved convergently. Arctometatarsalia has been dismantled and is no longer used by most paleontologists, with tyrannosauroids usually considered to be basal coelurosaurs outside Maniraptoriformes
. One recent analysis found the family Coeluridae
, including the Late Jurassic North American genera Coelurus
and Tanycolagreus
, to be the sister group of Tyrannosauroidea.
The most basal tyrannosauroid known from complete skeletal remains is Guanlong. Other early taxa include Stokesosaurus and Aviatyrannis, known from far less complete material. The better-known Dilong is considered slightly more derived than Guanlong and Stokesosaurus. Dryptosaurus
, long a difficult genus to classify, has turned up in several recent analyses as a basal tyrannosauroid as well, slightly more distantly related to Tyrannosauridae than Eotyrannus and Appalachiosaurus. Alectrosaurus
, a poorly known genus from Mongolia, is definitely a tyrannosauroid but its exact relationships are unclear. Other taxa have been considered possible tyrannosauroids by various authors, including Bagaraatan
, Labocania
and a species erroneously referred to Chilantaisaurus
, "C." maortuensis. Siamotyrannus
from the Early Cretaceous
of Thailand
was originally described as an early tyrannosaurid, but is usually considered a carnosaur today. Iliosuchus
has a vertical ridge on the ilium reminiscent of tyrannosauroids and may in fact be the earliest known member of the superfamily, but not enough material is known to be sure.
, which split from Gondwana
in the Middle Jurassic
, as well as on the northern continents, which separated from Laurasia later in the Mesozoic era. The earliest recognized tyrannosauroids lived in the Late Jurassic, including Guanlong from northwestern China, Stokesosaurus from the western United States and Aviatyrannis from Portugal. Some fossils currently referred to Stokesosaurus may instead belong to Aviatyrannis, given the great similarities in the dinosaur fauna
s of Portugal and North America during this time. If Iliosuchus from the Middle Jurassic of England is in fact a tyrannosauroid, it would be the earliest known genus and might suggest that the superfamily originated in Europe.
Early Cretaceous tyrannosauroids are also found on all three northern continents. Eotyrannus from England and Dilong from northeastern China are the only two named genera of this age, while Early Cretaceous tyrannosauroid premaxillary teeth are known from the Cedar Mountain Formation
in Utah
and the Tetori Group of Japan
.
By the middle of the Cretaceous, tyrannosauroid fossils are no longer found in Europe, suggesting a localized extinction on that continent. Tyrannosauroid teeth and possible body fossils are known from the North American Dakota Formation
, as well as formations in Kazakhstan
, Tajikstan and Uzbekistan
, from the middle of the Cretaceous. The first unquestionable remains of tyrannosaurids occur in the Campanian
stage
of the Late Cretaceous in North America and Asia. Two subfamilies are recognized. The albertosaurines are only known from North America, while the tyrannosaurines are found on both continents. Tyrannosaurid fossils have been found in Alaska
, which may have served as a land bridge allowing dispersal
between the two continents. Non-tyrannosaurid tyrannosauroids like Alectrosaurus and possibly Bagaraatan were contemporaneous with tyrannosaurids in Asia, while they are absent from western North America. Eastern North America was divided by the Western Interior Seaway
in the middle of the Cretaceous and isolated from the western portion of the continent. The absence of tyrannosaurids from the eastern part of the continent suggests that the family evolved after the appearance of the seaway, allowing basal tyrannosauroids like Dryptosaurus and Appalachiosaurus to survive in the east as a relict population until the end of the Cretaceous.
Basal
tyrannosauroids may have also been present in what is now southeastern Australia
during the Aptian
of the Early Cretaceous. NMV P186069, a partial pubis
(a hip bone) with a distinctive tyrannosauroid-like form, was discovered in Dinosaur Cove
in Victoria
, indicating that tyrannosauroids were not limited to the northern continents as previously thought.
An as of yet undescribed and unnamed tyrannosauroid from the Zuni Basin of New Mexico has been found.
structures have been preserved along with skeletal remains of numerous coelurosaurs from the Early Cretaceous Yixian Formation
and other nearby geological formations from Liaoning
, China. These filaments have usually been interpreted as "protofeathers," homologous
with the branched feathers found in birds and some non-avian theropods
, although other hypotheses have been proposed. A skeleton of Dilong was described in 2004 that included the first example of "protofeathers" in a tyrannosauroid. Similarly to down feather
s of modern birds, the "protofeathers" found in Dilong were branched but not pennaceous
, and may have been used for insulation
.
The presence of "protofeathers" in basal tyrannosauroids is not surprising, since they are now known to be characteristic of coelurosaurs, found in other basal genera like Sinosauropteryx
, as well as all more derived groups. Rare fossilized skin
impressions of large tyrannosaurids lack feathers, however, instead showing skin covered in scales
. It is possible that "protofeathers" were present on areas of the body not preserved with skin impressions. Alternatively, secondary loss of "protofeathers" in large tyrannosaurids may be analogous
with the similar loss of hair
in the largest modern mammals like elephant
s, where a low surface area
-to-volume
ratio slows down heat transfer
, making insulation by a coat of hair unnecessary.
Bony crests are found on the skulls of many theropods, including numerous tyrannosauroids. The most elaborate is found in Guanlong, where the nasal bones support a single, large crest which runs along the midline of the skull from front to back. This crest was penetrated by several large foramina (openings) which reduced its weight. A less prominent crest is found in Dilong, where low, parallel ridges run along each side of the skull, supported by the nasal and lacrimal bone
s. This ridges curve inwards and meet just behind the nostrils, making the crest Y-shaped. The fused nasals of tyrannosaurid are often very rough-textured. Alioramus
, a possible tyrannosaurid from Mongolia, bears a single row of five prominent bony bumps on the nasal bones; a similar row of much lower bumps is present on the skull of Appalachiosaurus, as well as some specimens of Daspletosaurus
, Albertosaurus, and Tarbosaurus. In Albertosaurus, Gorgosaurus and Daspletosaurus
, there is a prominent horn in front of each eye on the lacrimal bone. The lacrimal horn is absent in Tarbosaurus and Tyrannosaurus, which instead have a crescent-shaped crest behind each eye on the postorbital bone.
These head crests may have been used for display
, perhaps for species recognition or courtship behavior. An example of the handicap principle
may be the case of Guanlong, where the large, delicate crest may have been a hindrance to hunting in what was presumably an active predator. If an individual was healthy and successful at hunting despite the fragile crest, it would indicate the superior quality of the individual over others with smaller crests. Similarly to the unwieldy tail of a male peacock or the outsized antlers of an Irish elk
, the crest of Guanlong may have evolved via sexual selection
, providing an advantage in courtship which outweighed any decrease in hunting ability.
.
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
(or 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...
) of coelurosaurian theropod 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 that includes the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Tyrannosauridae
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
as well as more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
relatives. Tyrannosauroids lived on the Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
n supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
beginning in 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...
Period. By the end of the Cretaceous Period, tyrannosauroids were the dominant large predators in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
, culminating in the gigantic 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...
itself. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of tyrannosauroids have been recovered on what are now the continents of 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...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, 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...
, and possibly Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Tyrannosauroids were biped
Biped
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...
al carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s, as were most theropods, and were characterized by numerous skeletal features
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
, especially of the skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
and 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:...
. Early in their existence, tyrannosauroids were small predators with long, three-fingered forelimbs. 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...
genera became much larger, including some of the largest land-based predators ever to exist, but most of these later genera had proportionately small forelimbs with only two digits. Primitive feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
s have been found on Dilong
Dilong (dinosaur)
Dilong is a genus of small tyrannosauroid dinosaur. The only species is Dilong paradoxus. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of China. It lived about 130 million years ago...
, an early tyrannosauroid from China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, and may have been present in other tyrannosauroid genera as well. Prominent bony crests in a variety of shapes and sizes on the skulls of many tyrannosauroids may have served display
Display (zoology)
Display is a form of animal behaviour, linked to survival of the species in various ways. One example of display used by some species can be found in the form of courtship, with the male usually having a striking feature that is distinguished by colour, shape or size, used to attract a female...
functions.
Description
Tyrannosauroids varied widely in size, although there was a general trend towards increasing size over time. Early tyrannosauroids were small animals. One specimen of Dilong, almost fully grown, measured 1.6 meters (5.3 ft) in length, and a full-grown GuanlongGuanlong
Guanlong was a genus of proceratosaurid tyrannosauroid dinosaur, one of the earliest known examples of the lineage.-Description and discovery:...
measured 3 meters (10 ft long). Teeth from lower Lower Cretaceous rocks (140 to 136 million years old) of Hyogo, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, appear to have come from an approximately 5 metres (16.4 ft) long animal, possibly indicating an early size increase in the lineage. An immature Eotyrannus
Eotyrannus
Eotyrannus was a genus of tyrannosauroid theropod dinosaur hailing from the Early Cretaceous Wessex Formation beds, included in Wealden Group, located in the southwest coast of the Isle of Wight, United Kingdom...
was over 4 meters (13 ft) in length, and a subadult Appalachiosaurus
Appalachiosaurus
Appalachiosaurus is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal over 7 meters long and weighing over...
was estimated at more than 6 meters (20 ft) long, indicating that both genera reached larger sizes. The Late Cretaceous tyrannosaurids ranged from the 9 meter (30 ft) Albertosaurus
Albertosaurus
Albertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
and Gorgosaurus
Gorgosaurus
Gorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
to Tyrannosaurus, which exceeded 12 meters (40 ft) in length and may have weighed more than 6400 kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s (7 short 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). A 2010 review of the literature concluded that tyrannosaurs were "small- to mid-sized" for their first 80 million years but were "some of the largest terrestrial carnivores to ever live" in their last 20 million years.
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry bone is very tall, blunting the front of the snout, a feature which evolved convergently
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
in abelisaurids. The nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s are characteristically fused together, arched slightly upwards and often very roughly textured on their upper surface. The premaxillary teeth at the front of the upper jaw are shaped differently than the rest of the teeth, smaller in size and with a D-shaped cross section
Cross section (geometry)
In geometry, a cross-section is the intersection of a figure in 2-dimensional space with a line, or of a body in 3-dimensional space with a plane, etc...
. In the lower jaw
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
, a prominent ridge on the surangular bone
Suprangular
The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. It's usually in the back of the jaw, on the upper edge, and is connected to all other jaw bones: dentary, angular, splenial and articular. It is often a muscle attachment site....
extends sideways from just below the jaw joint, except in the basal Guanlong.
Tyrannosauroids had S-shaped necks and long tails, as did most other theropods. Early genera had long forelimbs, about 60% the length of the hindlimb in Guanlong, with the typical three digits of coelurosaurs. The long forelimb persisted at least through the Early Cretaceous Eotyrannus, but is unknown in Appalachiosaurus. Derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
tyrannosaurids have forelimbs strongly reduced in size, the most extreme example being Tarbosaurus
Tarbosaurus
Tarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
from 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...
, where the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
was only one-quarter the length of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
. The third digit of the forelimb was also reduced over time. This digit was unreduced in the basal Guanlong, but in Dilong it was significantly more slender than the other two digits. Eotyrannus still had three functional digits on each hand, but tyrannosaurids had only two, although the vestigial remnants of the third are found on some specimens. As in most coelurosaurs, the second digit of the hand is the largest, even when the third digit is not present.
Characteristic features of the tyrannosauroid pelvis include a concave notch at the upper front end of the ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, a sharply defined vertical ridge on the outside surface of the ilium, extending upwards from the acetabulum
Acetabulum
The acetabulum is a concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.-Structure:...
(hip socket), and a huge "boot" on the end of the pubis
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
, more than half as long as the shaft of the pubis itself. These features are found in all known tyrannosauroids, including basal members Guanlong and Dilong. The pubis is not known in Aviatyrannis
Aviatyrannis
Aviatyrannis is a genus of tyrannosauroid dinosaur from the Kimmeridgian stage of the Late Jurassic found in Portugal. It was described by Oliver Rauhut in 2003. The name means "Jurassic grandmother tyrant"...
or Stokesosaurus
Stokesosaurus
Stokesosaurus is a genus of small , early tyrannosaur from the Late Jurassic period of Utah and England. It was named after Utah geologist William Lee Stokes...
but both show typical tyrannosauroid characters in the ilium. The hindlimbs of all tyrannosauroids, like most theropods, had four toes, although the first toe (the hallux
Hallux
In tetrapods, the hallux is the innermost toe of the foot. Despite its name it may not be the longest toe on the foot of some individuals...
) did not contact the ground. Tyrannosauroid hindlimbs are longer relative to body size than almost any other theropods, and show proportions characteristic of fast-running
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...
animals, including elongated tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
e and metatarsals. These proportions persist even in the largest adult Tyrannosaurus, despite its probable inability to run. The third metatarsal of tyrannosaurids was pinched at the top between the second and fourth, forming a structure known as the arctometatarsus. The arctometatarsus was also present in Appalachiosaurus but it is unclear whether it was found in Eotyrannus or Dryptosaurus
Dryptosaurus
Dryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
. This structure was shared by derived ornithomimids, troodontids and caenagnathids, but was not present in basal tyrannosauroids like Dilong
Dilong
Dilong Ward is one of the sixteen wards of Mokokchung town. It is located in the lower slope of the town and forms the Northern part of Mokokchung....
, indicating convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
.
Taxonomy and systematics
Tyrannosaurus was named by Henry Fairfield OsbornHenry Fairfield Osborn
Henry Fairfield Osborn, Sr. ForMemRS was an American geologist, paleontologist, and eugenicist.-Early life and career:...
in 1905, along with the family Tyrannosauridae. The name is derived from the Ancient 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...
words τυραννος/tyrannos ('tyrant') and σαυρος/sauros ('lizard'). The superfamily name Tyrannosauroidea was first published in a 1964 paper by British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
paleontologist Alick Walker
Alick Walker
Alick Donald Walker was a British palaeontologist, after whom the Alwalkeria genus of dinosaur is named....
. The suffix
Suffix
In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns or adjectives, and verb endings, which form the conjugation of verbs...
-oidea, commonly used in the name of animal superfamilies, is derived from the Greek ειδος/eidos ('form').
Scientists have commonly understood Tyrannosauroidea to include the tyrannosaurids and their immediate ancestors. With the advent of phylogenetic taxonomy in vertebrate paleontology, however, 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...
has received several more explicit definitions. The first was by 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 1998, where Tyrannosauroidea was defined as a stem-based taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
including all species sharing a more recent common ancestor with Tyrannosaurus rex than with neornithean birds. To make the family more exclusive, Thomas Holtz redefined it in 2004 to include all species more closely related to Tyrannosaurus rex than to Ornithomimus velox, Deinonychus antirrhopus or Allosaurus fragilis. Sereno published a new definition in 2005, using Ornithomimus edmontonicus, Velociraptor mongoliensis and Troodon formosus as external specifiers. The Sereno definition was adopted in a 2010 review.
Classification
The following taxa are classified based on the latest studies of these animals.Superfamily Tyrannosauroidea
- Family CoeluridaeCoeluridaeCoeluridae is a historically polyphyletic family of generally small, carnivorous dinosaurs from the late Jurassic Period...
- Coelurus fragilisCoelurusCoelurus is a genus of coelurosaur dinosaur from the Late Jurassic period . The name means "hollow tail", referring to its hollow tail vertebrae...
(Late Jurassic, western North America) - Tanycolagreus topwilsoniTanycolagreusTanycolagreus is a genus of coelurid theropod from the Late Jurassic of North America. The holotype is a partial skeleton recovered from the Bone Cabin Quarry West locality, Albany County, Wyoming, from the Morrison Formation...
(Late Jurassic, western North America)
- Coelurus fragilis
- Family ProceratosauridaeProceratosauridaeProceratosauridae is a family or clade of theropod dinosaurs, probably belonging to the tyrannosaur lineage. It was first named in 2010 by Oliver Rauhut and colleagues in their re-evaluation of the type genus, Proceratosaurus...
- Kileskus aristotocusKileskusKileskus is a genus of tyrannosauroid dinosaur known from partial remains found in Middle Jurassic rocks of Krasnoyarsk Krai, Russia. Fossils recovered include the holotype maxilla, a premaxilla, a surangular, and a few bones from the hand and foot. The skull bones are similar to those of...
(Middle Jurassic, central RussiaRussiaRussia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
) - Guanlong wucaiiGuanlongGuanlong was a genus of proceratosaurid tyrannosauroid dinosaur, one of the earliest known examples of the lineage.-Description and discovery:...
(Late Jurassic, western ChinaChinaChinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
) - Proceratosaurus bradleyiProceratosaurusProceratosaurus is a genus of small-sized carnivorous theropod dinosaur from the Middle Jurassic of England. It was originally thought to be an ancestor of Ceratosaurus, due to the similar small crest on its snout...
(Middle Jurassic, EnglandEnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
) - Sinotyrannus kazuoensisSinotyrannusSinotyrannus is a genus of large basal proceratosaurid dinosaur, a relative of tyrannosaurids which flourished in North America and Asia during the Jurassic and early Cretaceous periods. Sinotyrannus is known from a single incomplete fossil specimen including a partial skull, from the Early...
(Early Cretaceous, eastern China)
- Kileskus aristotocus
- Dilong paradoxusDilong (dinosaur)Dilong is a genus of small tyrannosauroid dinosaur. The only species is Dilong paradoxus. It is from the Lower Cretaceous Yixian Formation near Lujiatun, Beipiao, in the western Liaoning province of China. It lived about 130 million years ago...
(Early CretaceousEarly CretaceousThe Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
, eastern China) - Eotyrannus lengiEotyrannusEotyrannus was a genus of tyrannosauroid theropod dinosaur hailing from the Early Cretaceous Wessex Formation beds, included in Wealden Group, located in the southwest coast of the Isle of Wight, United Kingdom...
(Early Cretaceous, England) - Stokesosaurus clevelandiStokesosaurusStokesosaurus is a genus of small , early tyrannosaur from the Late Jurassic period of Utah and England. It was named after Utah geologist William Lee Stokes...
(Late Jurassic, western North AmericaNorth AmericaNorth 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...
) - Stokesosaurus langhamiStokesosaurusStokesosaurus is a genus of small , early tyrannosaur from the Late Jurassic period of Utah and England. It was named after Utah geologist William Lee Stokes...
(Late Jurassic, EnglandEnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
) - Aviatyrannis jurassicaAviatyrannisAviatyrannis is a genus of tyrannosauroid dinosaur from the Kimmeridgian stage of the Late Jurassic found in Portugal. It was described by Oliver Rauhut in 2003. The name means "Jurassic grandmother tyrant"...
(Late JurassicLate JurassicThe Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
, PortugalPortugalPortugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
) - Xiongguanlong baimoensisXiongguanlongXiongguanlong is a genus of tyrannosauroid dinosaur that lived in the Early Cretaceous of what is now China. The type species is X. baimoensis, described online in 2009 by a group of researchers from China and the United States, and formally published in January 2010. The genus name refers to the...
(Early Cretaceous, central China) - Family Dryptosauridae
- Dryptosaurus aquilunguisDryptosaurusDryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
(Late Cretaceous, eastern North America)
- Dryptosaurus aquilunguis
- Appalachiosaurus montgomeriensisAppalachiosaurusAppalachiosaurus is a genus of tyrannosauroid theropod dinosaur from the Late Cretaceous Period of eastern North America. Like almost all theropods, it was a bipedal predator. Only a juvenile skeleton has been found, representing an animal over 7 meters long and weighing over...
(Late Cretaceous, eastern North America) - Labocania anomalaLabocaniaLabocania is a genus of theropod, possibly tyrannosauroid, dinosaur from Baja California, Mexico, which lived 70 million years ago, in the Campanian stage of the late Cretaceous Period. The name references the "La Bocana Roja" Formation, which translates as "red lips". The type species, L....
(Late Cretaceous, western MexicoMexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
) - Bistahieversor sealeyiBistahieversorBistahieversor is a genus of tyrannosauroid dinosaur. Bistahieversor existed around 75 million years ago during the Late Cretaceous....
(Late CretaceousLate CretaceousThe 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...
, New MexicoNew MexicoNew 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...
, United StatesUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
) - Family TyrannosauridaeTyrannosauridaeTyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
- Subfamily Albertosaurinae
- Alectrosaurus olseniAlectrosaurusAlectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
(Late Cretaceous, Mongolia) - Albertosaurus sarcophagusAlbertosaurusAlbertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
(Late Cretaceous, western North America) - Gorgosaurus libratusGorgosaurusGorgosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, between about 76.5 and 75 million years ago. Fossil remains have been found in the Canadian province of Alberta and possibly the U.S. state of Montana....
(Late Cretaceous, western North America)
- Alectrosaurus olseni
- Subfamily Tyrannosaurinae
- Alioramus remotusAlioramusAlioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
(Late Cretaceous, Mongolia) - Alioramus altaiAlioramusAlioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
(Late Cretaceous, Mongolia) - Teratophoneus currieiTeratophoneusTeratophoneus is a genus of carnivorous tyrannosaurid theropod dinosaur which lived during the late Cretaceous period in what is now Utah, USA. It is known from an incomplete skull and postcranial skeleton recovered from the Kaiparowits Formation. Teratophoneus was named by Thomas D. Carr, Thomas E...
(Late Cretaceous, western North America) - Daspletosaurus torosusDaspletosaurusDaspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
(Late Cretaceous, western North America) - Zhuchengtyrannus magnusZhuchengtyrannusZhuchengtyrannus is an extinct genus of carnivorous theropod dinosaur from the Late Cretaceous period. It is a tyrannosaurine tyrannosaurid which lived during the late Cretaceous period in what is now Zhucheng, Shandong Province of China...
(Late Cretaceous, China) - Tarbosaurus bataarTarbosaurusTarbosaurus is a genus of tyrannosaurid theropod dinosaur that flourished in Asia about 70 million years ago, at the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia, with more fragmentary remains found further afield in parts of China. Although many species have been...
(Late Cretaceous, Mongolia) - Tyrannosaurus rexTyrannosaurusTyrannosaurus 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...
(Late Cretaceous, western North America)
- Alioramus remotus
- Subfamily Albertosaurinae
- Questionable/Dubious Placement
- Iliosuchus incognithusIliosuchusIliosuchus is a genus of theropod dinosaur known from Bathonian–age rocks of England. It was perhaps long....
(Middle JurassicMiddle JurassicThe Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
, EnglandEnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
; too fragmentary to work with) - Bagaraatan ostromiBagaraatanBagaraatan was a genus of theropod dinosaur from the Late Cretaceous period. Its fossils were found in the Nemegt Formation of Mongolia. Bagaraatan may have been around 3–4 metres in length....
(Late CretaceousLate CretaceousThe 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...
, MongoliaMongoliaMongolia 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...
; might be a maniraptoran instead) - Diplotomodon horrificusDiplotomodonDiplotomodon is a dubious genus of dinosaur from New Jersey. It is only known from a single tooth found in either the Navesink or Hornerstown Formation, dating to the Maastrichtian age of the late Cretaceous period...
(Late Cretaceous, New JerseyNew JerseyNew Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
, United States; may be synonymous with either DryptosaurusDryptosaurusDryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
species) - Dryptosaurus macropusDryptosaurusDryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
(Late Cretaceous, eastern North America; too fragmentary may belong to another kind of theropod) - Dryptosaurus falculusDryptosaurusDryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
(Late Cretaceous, eastern North America; too fragmentary may belong to another kind of theropod) - Dryptosaurus hazenianusDryptosaurusDryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
(Late Cretaceous, eastern North America; too fragmentary may belong to another kind of theropod) - All AublysodonAublysodonAublysodon is a name given to a large number of carnivorous dinosaur teeth of a certain form found in numerous late Cretaceous period geological formations...
sp. (Late Cretaceous, western North America; based on teeth alone) - All DeinodonDeinodonDeinodon is a name assigned to tyrannosaurid teeth of the Late Cretaceous of Montana by paleontologist Joseph Leidy in 1856...
sp. (Late Cretaceous, western North America; based on teeth alone) - Raptorex kriegsteiniRaptorexRaptorex is a dubious genus of tyrannosaurid dinosaur. Its fossil remains consist of a single juvenile specimen probably uncovered in Mongolia, or possibly northeastern China. The type species is R. kriegsteini, described in 2009 by Sereno and colleagues. The genus name is derived from Latin ,...
(Late Cretaceous?, Mongolia?; might represent a juvenile specimen of Tarbosaurus bataar instead.) - Nanotyrannus lancensisNanotyrannusNanotyrannus is a genus of tyrannosaurid dinosaur, known only from two juvenile specimens, which may in fact represent juvenile specimens of the contemporary species Tyrannosaurus rex.-History:...
(Late Cretaceous, western North America; might represent juvenile specimens of Tyrannosaurus rex instead.)
- Iliosuchus incognithus
Phylogeny
While paleontologists have long recognized the family Tyrannosauridae, its ancestry has been the subject of much debate. For most of the twentieth century, tyrannosaurids were commonly accepted as members of the CarnosauriaCarnosauria
Carnosauria is a group of large predatory dinosaurs that lived during the Jurassic and Cretaceous periods. While it originally contained a wide assortment of giant theropods that were not closely related, the group has since been defined to encompass only the allosaurs and their closest kin...
, which included almost all large theropods. Within this group, the allosaurid
Allosaurid
Allosauridae was a family of medium to large sized carnivorous theropod dinosaurs. Members included Saurophaganax, Allosaurus, and the poorly known Epanterias, which could well be a specimen of Allosaurus...
s were often considered to be ancestral to tyrannosaurids. In the early 1990s, cladistic analyses instead began to place tyrannosaurids into the Coelurosauria, echoing suggestions first published in the 1920s. Tyrannosaurids are now universally considered to be large coelurosaurs.
Thomas Carr (paleontologist)
Thomas D. Carr is a vertebrate paleontologist who received his Ph.D. from the University of Toronto in 2005. He is now a member of the biology faculty at Carthage College in Kenosha, Wisconsin. Much of his work centers on tyrannosauroid dinosaurs...
et al. 2005
In 1994, Holtz grouped tyrannosauroids with elmisaurids, ornithomimosaurs and troodonts into a coelurosaurian clade called Arctometatarsalia based on a common ankle structure where the second and fourth metatarsals meet near the tarsal
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
bones, covering the third metatarsal when viewed from the front. Basal tyrannosauroids like Dilong, however, were found with non-arctometatarsalian
Arctometatarsalian
An arctometatarsalian organism is one in which the proximal part of the third metatarsal is pinched between metatarsals II and IV. The trait appears to be highly homoplastic, common in certain sorts of dinosaurs accustomed to running , to evenly transmit force to the metatarsals....
ankles, indicating that this feature evolved convergently. Arctometatarsalia has been dismantled and is no longer used by most paleontologists, with tyrannosauroids usually considered to be basal coelurosaurs outside Maniraptoriformes
Maniraptoriformes
Maniraptoriformes is a clade of dinosaurs that contains ornithomimosaurs and maniraptors. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of Ornithomimus and birds, and all descendants of that common ancestor."...
. One recent analysis found the family Coeluridae
Coeluridae
Coeluridae is a historically polyphyletic family of generally small, carnivorous dinosaurs from the late Jurassic Period...
, including the Late Jurassic North American genera Coelurus
Coelurus
Coelurus is a genus of coelurosaur dinosaur from the Late Jurassic period . The name means "hollow tail", referring to its hollow tail vertebrae...
and Tanycolagreus
Tanycolagreus
Tanycolagreus is a genus of coelurid theropod from the Late Jurassic of North America. The holotype is a partial skeleton recovered from the Bone Cabin Quarry West locality, Albany County, Wyoming, from the Morrison Formation...
, to be the sister group of Tyrannosauroidea.
The most basal tyrannosauroid known from complete skeletal remains is Guanlong. Other early taxa include Stokesosaurus and Aviatyrannis, known from far less complete material. The better-known Dilong is considered slightly more derived than Guanlong and Stokesosaurus. Dryptosaurus
Dryptosaurus
Dryptosaurus was a genus of primitive tyrannosaur that lived in Eastern North America during the middle Maastrichtian stage of the Late Cretaceous period. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R...
, long a difficult genus to classify, has turned up in several recent analyses as a basal tyrannosauroid as well, slightly more distantly related to Tyrannosauridae than Eotyrannus and Appalachiosaurus. Alectrosaurus
Alectrosaurus
Alectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
, a poorly known genus from Mongolia, is definitely a tyrannosauroid but its exact relationships are unclear. Other taxa have been considered possible tyrannosauroids by various authors, including Bagaraatan
Bagaraatan
Bagaraatan was a genus of theropod dinosaur from the Late Cretaceous period. Its fossils were found in the Nemegt Formation of Mongolia. Bagaraatan may have been around 3–4 metres in length....
, Labocania
Labocania
Labocania is a genus of theropod, possibly tyrannosauroid, dinosaur from Baja California, Mexico, which lived 70 million years ago, in the Campanian stage of the late Cretaceous Period. The name references the "La Bocana Roja" Formation, which translates as "red lips". The type species, L....
and a species erroneously referred to Chilantaisaurus
Chilantaisaurus
Chilantaisaurus is a genus of neovenatorid theropod dinosaur 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 and...
, "C." maortuensis. Siamotyrannus
Siamotyrannus
Siamotyrannus is a genus of theropod dinosaur from the early Cretaceous . It is known from a partial skeleton which includes part of the pelvis, the sacrum, and a number of vertebrae. The fossils were found in 1993 by Somchai Traimwichanon in the Sao Khua Formation of northeastern Thailand...
from the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
of Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
was originally described as an early tyrannosaurid, but is usually considered a carnosaur today. Iliosuchus
Iliosuchus
Iliosuchus is a genus of theropod dinosaur known from Bathonian–age rocks of England. It was perhaps long....
has a vertical ridge on the ilium reminiscent of tyrannosauroids and may in fact be the earliest known member of the superfamily, but not enough material is known to be sure.
Distribution
The tyrannosauroids lived on the supercontinent LaurasiaLaurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
, which split from Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
in the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
, as well as on the northern continents, which separated from Laurasia later in the Mesozoic era. The earliest recognized tyrannosauroids lived in the Late Jurassic, including Guanlong from northwestern China, Stokesosaurus from the western United States and Aviatyrannis from Portugal. Some fossils currently referred to Stokesosaurus may instead belong to Aviatyrannis, given the great similarities in the dinosaur fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
s of Portugal and North America during this time. If Iliosuchus from the Middle Jurassic of England is in fact a tyrannosauroid, it would be the earliest known genus and might suggest that the superfamily originated in Europe.
Cedar Mountain Formation
The Cedar Mountain Formation is the name given to distinctive sedimentary rocks in eastern Utah that occur between the underlying Morrison Formation and overlying Naturita Formation . It is composed of non-marine sediments, that is, sediments deposited in rivers, lakes and on flood plains...
in 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 the Tetori Group of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
.
By the middle of the Cretaceous, tyrannosauroid fossils are no longer found in Europe, suggesting a localized extinction on that continent. Tyrannosauroid teeth and possible body fossils are known from the North American Dakota Formation
Dakota Formation
The Dakota Formation is a geologic formation composed of sedimentary rocks deposited on the western side of the Late Cretaceous Western Interior Seaway. F.B. Meek and F.V. Hayden named it for exposures along the Missouri River near Dakota City, Nebraska...
, as well as formations in Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
, Tajikstan and Uzbekistan
Uzbekistan
Uzbekistan , officially the Republic of Uzbekistan is a doubly landlocked country in Central Asia and one of the six independent Turkic states. It shares borders with Kazakhstan to the west and to the north, Kyrgyzstan and Tajikistan to the east, and Afghanistan and Turkmenistan to the south....
, from the middle of the Cretaceous. The first unquestionable remains of tyrannosaurids occur in the Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
of the Late Cretaceous in North America and Asia. Two subfamilies are recognized. The albertosaurines are only known from North America, while the tyrannosaurines are found on both continents. Tyrannosaurid fossils have been found in Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, which may have served as a land bridge allowing dispersal
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
between the two continents. Non-tyrannosaurid tyrannosauroids like Alectrosaurus and possibly Bagaraatan were contemporaneous with tyrannosaurids in Asia, while they are absent from western North America. Eastern North America was divided by the Western Interior Seaway
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
in the middle of the Cretaceous and isolated from the western portion of the continent. The absence of tyrannosaurids from the eastern part of the continent suggests that the family evolved after the appearance of the seaway, allowing basal tyrannosauroids like Dryptosaurus and Appalachiosaurus to survive in the east as a relict population until the end of the Cretaceous.
Basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
tyrannosauroids may have also been present in what is now southeastern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
during the Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
of the Early Cretaceous. NMV P186069, a partial pubis
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
(a hip bone) with a distinctive tyrannosauroid-like form, was discovered in Dinosaur Cove
Dinosaur Cove
Not to be confused with the children's book series of the same name.Dinosaur Cove in Victoria, Australia is a fossil bearing site in south-east of the continent where the Otway Ranges meet the sea to the west of Cape Otway, adjacent to Great Otway National Park .The inaccessible ocean-front cliffs...
in Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
, indicating that tyrannosauroids were not limited to the northern continents as previously thought.
An as of yet undescribed and unnamed tyrannosauroid from the Zuni Basin of New Mexico has been found.
Feathers
Long filamentousProtein filament
In biology, a filament is a "long chain of proteins, such as those found in hair, muscle, or in flagella". They are often bundled together for strength and rigidity. Some cellular examples include:*Actin filaments*Microtubules*Intermediate filaments...
structures have been preserved along with skeletal remains of numerous coelurosaurs from the Early Cretaceous Yixian Formation
Yixian Formation
The Yixian Formation is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans 11 million years during the early Cretaceous period...
and other nearby geological formations from Liaoning
Liaoning
' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...
, China. These filaments have usually been interpreted as "protofeathers," homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
with the branched feathers found in birds and some non-avian theropods
Feathered dinosaurs
The realization that dinosaurs are closely related to birds raised the obvious possibility of feathered dinosaurs. Fossils of Archaeopteryx include well-preserved feathers, but it was not until the early 1990s that clearly non-avialan dinosaur fossils were discovered with preserved feathers...
, although other hypotheses have been proposed. A skeleton of Dilong was described in 2004 that included the first example of "protofeathers" in a tyrannosauroid. Similarly to down feather
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,...
s of modern birds, the "protofeathers" found in Dilong were branched but not pennaceous
Pennaceous feather
Pennaceous feathers are also known as contour feathers. This type of feather is present in most modern birds, and has been shown in some species of maniraptoran dinosaurs....
, and may have been used for insulation
Thermal insulation
Thermal insulation is the reduction of the effects of the various processes of heat transfer between objects in thermal contact or in range of radiative influence. Heat transfer is the transfer of thermal energy between objects of differing temperature...
.
The presence of "protofeathers" in basal tyrannosauroids is not surprising, since they are now known to be characteristic of coelurosaurs, found in other basal genera like 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 all more derived groups. Rare fossilized skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
impressions of large tyrannosaurids lack feathers, however, instead showing skin covered in scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
. It is possible that "protofeathers" were present on areas of the body not preserved with skin impressions. Alternatively, secondary loss of "protofeathers" in large tyrannosaurids may be analogous
Analogy (biology)
An analogy is a trait or an organ that appears similar in two unrelated organisms. The cladistic term for the same phenomenon is homoplasy, from Greek for same form. Biological anologies are often the result of convergent evolution....
with the similar loss of hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....
in the largest modern mammals like elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
s, where a low surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
-to-volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
ratio slows down heat transfer
Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
, making insulation by a coat of hair unnecessary.
Head crests
Lacrimal bone
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
s. This ridges curve inwards and meet just behind the nostrils, making the crest Y-shaped. The fused nasals of tyrannosaurid are often very rough-textured. Alioramus
Alioramus
Alioramus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous period of Asia. The type A. remotus, is known from a partial skull and three metatarsals recovered from Mongolian sediments which were deposited in a humid floodplain between 70 and 65 million years ago. These...
, a possible tyrannosaurid from Mongolia, bears a single row of five prominent bony bumps on the nasal bones; a similar row of much lower bumps is present on the skull of Appalachiosaurus, as well as some specimens of Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, Albertosaurus, and Tarbosaurus. In Albertosaurus, Gorgosaurus and Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, there is a prominent horn in front of each eye on the lacrimal bone. The lacrimal horn is absent in Tarbosaurus and Tyrannosaurus, which instead have a crescent-shaped crest behind each eye on the postorbital bone.
These head crests may have been used for display
Display (zoology)
Display is a form of animal behaviour, linked to survival of the species in various ways. One example of display used by some species can be found in the form of courtship, with the male usually having a striking feature that is distinguished by colour, shape or size, used to attract a female...
, perhaps for species recognition or courtship behavior. An example of the handicap principle
Handicap principle
The handicap principle is a hypothesis originally proposed in 1975 by biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signaling between animals who have an obvious motivation to bluff or deceive each other...
may be the case of Guanlong, where the large, delicate crest may have been a hindrance to hunting in what was presumably an active predator. If an individual was healthy and successful at hunting despite the fragile crest, it would indicate the superior quality of the individual over others with smaller crests. Similarly to the unwieldy tail of a male peacock or the outsized antlers of an Irish elk
Irish Elk
The Irish Elk or Giant Deer , was a species of Megaloceros and one of the largest deer that ever lived. Its range extended across Eurasia, from Ireland to east of Lake Baikal, during the Late Pleistocene. The latest known remains of the species have been carbon dated to about 7,700 years ago...
, the crest of Guanlong may have evolved via sexual selection
Sexual selection
Sexual selection, a concept introduced by Charles Darwin in his 1859 book On the Origin of Species, is a significant element of his theory of natural selection...
, providing an advantage in courtship which outweighed any decrease in hunting ability.
Reproduction
Neonate sized tyrannosaur fossils have been documented in the scientific literatureScientific literature
Scientific literature comprises scientific publications that report original empirical and theoretical work in the natural and social sciences, and within a scientific field is often abbreviated as the literature. Academic publishing is the process of placing the results of one's research into the...
.
External links
- List of tyrannosauroid specimens and species at The Theropod Database.