Tyrannosauroidea

Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian 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. Fossils of tyrannosauroids have been recovered on what are now the continents of North America, Europe, Asia, South America and Australia.

Tyrannosauroids were bipedal carnivores, 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 feathers have been identified in fossils of two species, and may have been present in other tyrannosauroids as well. Prominent bony crests in a variety of shapes and sizes on the skulls of many tyrannosauroids may have served display functions.

Tyrannosauroids
Temporal range:
Middle JurassicLate Cretaceous, 165–66 Ma
Leaping Yutyrannus Mount Laika AC
Replica skeletons of Yutyrannus huali
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Coelurosauria
Clade: Tyrannoraptora
Superfamily: Tyrannosauroidea
Osborn, 1906 (vide Walker, 1964)
Type species
Tyrannosaurus rex
Osborn, 1905
Subgroups

Description

Tyrannosauroidea size 01
Size of some small genera, compared to a human.

Tyrannosauroids varied widely in size, although there was a general trend towards increasing size over time. Early tyrannosauroids were small animals.[1] One specimen of Dilong, almost fully grown, measured 1.6 meters (5.3 ft) in length,[2] and a fully-grown Guanlong measured 3 meters (10 ft long).[3] 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 ft) long animal, possibly indicating an early size increase in the lineage.[4] An immature Eotyrannus was over 4 meters (13 ft) in length,[5] and a subadult Appalachiosaurus was estimated at more than 6 meters (20 ft) long,[1] 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 (39 ft) in length and may have weighed more than 6400 kilograms (7 short tons).[1] 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.[6][7]

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 premaxillary bone is very tall, blunting the front of the snout, a feature which evolved convergently in abelisaurids. The nasal bones 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 from 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.[1][2][3]

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.[3] The long forelimb persisted at least through the Early Cretaceous Eotyrannus,[5] but is unknown in Appalachiosaurus.[8] 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.[1] The third digit of the forelimb was also reduced over time. This digit was unreduced in the basal Guanlong,[3] while in Dilong it was more slender than the other two digits.[2] Eotyrannus also had three functional digits on each hand.[5] Tyrannosaurids had only two, although the vestigial metacarpal of the third are preserved in some well-preserved specimens.[9] 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.[1] These features are found in all known tyrannosauroids, including basal members Guanlong[3] and Dilong.[2] The pubis is not known in Aviatyrannis or Stokesosaurus but both show typical tyrannosauroid characters in the ilium.[10] 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 tibiae and metatarsals.[1] These proportions persist even in the largest adult Tyrannosaurus,[11] despite its probable inability to run.[12] The third metatarsal of tyrannosaurids was pinched at the top between the second and fourth, forming a structure known as the arctometatarsus.[1] The arctometatarsus was also present in Appalachiosaurus[8] but it is unclear whether it was found in Eotyrannus[5] or Dryptosaurus.[13] This structure was shared by derived ornithomimids, troodontids and caenagnathids,[14] but was not present in basal tyrannosauroids like Dilong, indicating convergent evolution.[2]

Classification

Tyrannosaurus was named by Henry Fairfield Osborn in 1905, along with the family Tyrannosauridae.[15] 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 the British paleontologist Alick Walker.[16] The suffix -oidea, commonly used in the name of animal superfamilies, is derived from the Greek ειδος/eidos ('form').[17]

Proceratosaurus holotype
Skull of Proceratosaurus, a proceratosaurid from the Middle Jurassic of England.
Appalachiosaurus
Skeleton of Appalachiosaurus, a non-tyrannosaurid tyrannosauroid from the Late Cretaceous of Eastern North America.

Scientists have commonly understood Tyrannosauroidea to include the tyrannosaurids and their immediate ancestors.[16][18] 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.[19] 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.[1] Sereno published a new definition in 2005, using Ornithomimus edmontonicus, Velociraptor mongoliensis and Troodon formosus as external specifiers.[20] The Sereno definition was adopted in a 2010 review.[6]

Some studies have suggested that the clade Megaraptora, usually considered to be allosauroids, are basal tyrannosauroids.[21][22] However, other authors disputed the placement of megaraptorans within Tyrannosauroidea,[23][24] and a study of megaraptoran hand anatomy published in 2016 caused even the original scientists suggesting their tyrannosauroid relationships to at least partly reject their prior conclusion.[25]

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 Carnosauria, which included almost all large theropods.[26][27] Within this group, the allosaurids were often considered to be ancestral to tyrannosaurids.[18][28] In the early 1990s, cladistic analyses instead began to place tyrannosaurids into the Coelurosauria,[14][29] echoing suggestions first published in the 1920s.[30][31] Tyrannosaurids are now universally considered to be large coelurosaurs.[1][3][32][33][34][35][36]

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.[14] Basal tyrannosauroids like Dilong, however, were found with non-arctometatarsalian ankles, indicating that this feature evolved convergently.[2] Arctometatarsalia has been dismantled and is no longer used by most paleontologists, with tyrannosauroids usually considered to be basal coelurosaurs outside Maniraptoriformes.[1][34][36] One recent analysis found the family Coeluridae, including the Late Jurassic North American genera Coelurus and Tanycolagreus, to be the sister group of Tyrannosauroidea.[32]

The most basal tyrannosauroid known from complete skeletal remains is Guanlong, a representative of the family Proceratosauridae.[3][37] Other early taxa include Stokesosaurus and Aviatyrannis, known from far less complete material.[10] The better-known Dilong is considered slightly more derived than Guanlong and Stokesosaurus.[2][3] 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.[1][8][38] Alectrosaurus, a poorly known genus from Mongolia, is definitely a tyrannosauroid but its exact relationships are unclear.[1] Other taxa have been considered possible tyrannosauroids by various authors, including Bagaraatan and Labocania.[1] Siamotyrannus from the Early Cretaceous of Thailand was originally described as an early tyrannosaurid,[39] but is usually considered a carnosaur today.[34][40] 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.[10][40]

Below is a cladogram by Loewen et al. in 2013 that included most tyrannosauroid species known at the time of its publication.[41]

Tyrannosauroidea
Proceratosauridae

Proceratosaurus bradleyi

Kileskus aristotocus

Guanlong wucaii Guanlong wucaii by durbed flipped

Sinotyrannus kazuoensis S. kazuoensis restoration (flipped)

Juratyrant langhami

Stokesosaurus clevelandiStokesosaurus by Tom Parker

Dilong paradoxus

Eotyrannus lengi

Bagaraatan ostromi

Raptorex kriegsteini

Dryptosaurus aquilunguisDryptosaurus by Durbed

Alectrosaurus olseniAlectrosaurus flipped

Xiongguanlong baimoensis

Appalachiosaurus montgomeriensisAppalachiosaurus montgomeriensis flipped

Alioramus altaiAlioramus Life Restoration flipped

Alioramus remotus

Tyrannosauridae

Gorgosaurus libratusGorgosaurus flipped

Albertosaurus sarcophagus

Tyrannosaurinae

Daspletosaurus torosusDaspletosaurus torosus steveoc flipped

Teratophoneus curriei

Bistahieversor sealeyi

Lythronax argestesLythronax by Tomopteryx flipped

Tyrannosaurus rexTyrannosaurus-rex-Profile-steveoc86

Tarbosaurus bataarTarbosaurus Steveoc86 flipped

Zhuchengtyrannus magnus

Distribution

The tyrannosauroids lived on the supercontinent Laurasia, 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 Middle-Late Jurassic, including Guanlong and Kileskus from the Far East, Stokesosaurus from the western United States and Aviatyrannis, Juratyrant, and Proceratosaurus from Europe.

Tyrannosauroid fossil localities map
Confirmed tyrannosauroid fossils have only been discovered in the northern continents, with possible basal tyrannosauroid fossils reported from Australia. Late Cretaceous tyrannosauroids are known only from North America and Asia.

Early Cretaceous tyrannosauroids are known from Laurasia, being represented by Eotyrannus from England[5] and Dilong, Sinotyrannus, and Yutyrannus from northeastern China. Early Cretaceous tyrannosauroid premaxillary teeth are known from the Cedar Mountain Formation in Utah[42] and the Tetori Group of Japan.[43]

The Middle Cretaceous record of Tyrannosauroidea is rather patchy. Teeth and indeterminate postcrania of this interval are known from the Cenomanian-age Dakota Formation of western North America and Potomac Formation of New Jersey,[42][44] as well as formations in Kazakhstan and Tajikistan;[45] two genera, Timurlengia and Xiongguanlong, have been found in Asia, while the Brazilian Santanaraptor may belong to this group.[46] Suskityrannus has been found in the Moreno Hill Formation of the Zuni Basin of western New Mexico.[47][48] 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.[1] Tyrannosaurid fossils have been found in Alaska, which may have served as a land bridge allowing dispersal between the two continents.[49] Non-tyrannosaurid tyrannosauroids like Alectrosaurus and possibly Bagaraatan were contemporaneous with tyrannosaurids in Asia, while they are absent from western North America.[1] 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.[8]

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.[50]

Paleobiology

Feathers

Long filamentous 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.[51] These filaments have usually been interpreted as "protofeathers," homologous with the branched feathers found in birds and some non-avian theropods,[52][53] although other hypotheses have been proposed.[54] A skeleton of Dilong was described in 2004 that included the first example of feathers in a tyrannosauroid. Similarly to down feathers of modern birds, the feathers found in Dilong were branched but not pennaceous, and may have been used for insulation.[2] Even large tyrannosauroids have been found with evidence of feathers. Yutyrannus huali, also from the Yixian Formation, is known from three specimens, each preserving traces of feathers on various parts of the body. While not all areas of the body preserve impressions across all three specimens, these fossils demonstrate that even in this medium-sized species, most of the body was covered in feathers.[55]

The presence of feathers in basal tyrannosauroids is not surprising, since they are now known to be characteristic of coelurosaurs, found in other basal genera like Sinosauropteryx,[52] as well as all more derived groups.[51] Rare fossilized skin impressions of some Late Cretaceous tyrannosaurids lack feathers, however, instead showing skin covered in fine, non-overlapping scales.[56] It is possible that feathers were present on other areas of the body: Preserved skin impressions are very small and come primarily from the legs, pelvic region, and underside of the tail, which either lack feathers or only covered in a light down in some modern larger ground-dwelling birds. Alternatively, secondary loss of feathers in large tyrannosaurids may be analogous with the similar loss of hair in the largest modern mammals like elephants, where a low surface area-to-volume ratio slows down heat transfer, making insulation by a coat of hair unnecessary or even detrimental.[2] A precedent can be seen in other dinosaur groups such as ornithischians, in which filamentous structures were lost and scales reappeared.[57]

Head crests

Guanlong wucaii head
The elaborate head crest of Guanlong, a basal tyrannosauroid from China.

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.[3] 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 bones. These ridges curve inwards and meet just behind the nostrils, making the crest Y-shaped.[2] The fused nasals of tyrannosaurids 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.[8] 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.[1]

These head crests may have been used for display, perhaps for species recognition or courtship behavior.[1] 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 that outweighed any decrease in hunting ability.[3]

Reproduction

Neonate sized tyrannosaur fossils have been documented in the scientific literature.[58]

References

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External links

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Alioramus

Alioramus (; meaning 'different branch') is a genus of tyrannosaurid theropod dinosaurs from the Late Cretaceous period of Asia. The type species, A. remotus, is known from a partial skull and three foot bones recovered from Mongolian sediments which were deposited in a humid floodplain about 70 million years ago. These remains were named and described by Soviet paleontologist Sergei Kurzanov in 1976. A second species, A. altai, known from a much more complete skeleton, was named and described by Stephen L. Brusatte and colleagues in 2009. Its relationships to other tyrannosaurid genera are unclear, with some evidence supporting a hypothesis that Alioramus is closely related to the contemporary species Tarbosaurus bataar. A possible third species, A. sinensis was described in 2014 on the basis of fossils found in the Nanxiong Formation of China.Alioramus were bipedal like all known theropods, and their sharp teeth indicate that they were carnivores. Known specimens were smaller than other tyrannosaurids like Tarbosaurus bataar and Tyrannosaurus rex, but their adult size is difficult to estimate since both Alioramus species are known only from juvenile or sub-adult remains. The recent discovery of Qianzhousaurus indicates that it belongs to a distinct branch of tyrannosaur. The genus Alioramus is characterized by a row of five bony crests along the top of the snout, a greater number of teeth than any other genus of tyrannosaurid, and a lower skull than most other tyrannosaurids.

Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Aviatyrannis

Aviatyrannis is a genus of carnivorous tyrannosauroid theropod dinosaur from the Kimmeridgian stage of the Late Jurassic found in Portugal.

In 2000 Oliver Walter Mischa Rauhut reported the find of tyrannosauroid material in the lignite coal mine of Guimarota near Leiria, which he referred to Stokesosaurus. Later concluding the distinctiveness of the material justified a separate genus, Rauhut in 2003 named and described it as the type species Aviatyrannis jurassica. The species name was by Rauhut given the intended meaning of "tyrant's grandmother from the Jurassic". The generic name is derived from Latin avia, "grandmother", and tyrannus, "tyrant", on the presumption tyrannis would be its genitive. The specific name means "Jurassic".The holotype, IPFUB Gui Th 1, was found in a layer of the Alcobaça Formation dating from the early Kimmeridgian, about 155 million years old. It consists of a right ilium. Rauhut in 2003 referred two other bones to Aviatyrannis: IPFUB Gui Th 2, a partial right ilium, and IPFUB Gui Th 3, a right ischium. The referred elements represent slightly larger individuals. Additionally sixteen isolated teeth were referred: IPFUB GUI D 89-91: three teeth of the premaxilla, and IPFUB GUI D 174-186: thirteen teeth of the maxilla and dentary. These had in 1998 been described by Jens Zinke. Rauhut also hypothesised that a number of specimens referred to Stokesosaurus might actually belong to Aviatyrannis.

Like other early tyrannosauroids, Aviatyrannis was a rather small bipedal predator. The holotype specimen IPFUB Gui Th 1, for example, is an ilium only ninety millimeters long. It may have belonged to a juvenile. In 2010 Gregory S. Paul estimated its length at one metre, its weight at five kilogrammes. The ilium is elongated and low with the typical tyrannosauroid vertical ridge on the outer blade surface above the hip joint. The teeth of the praemaxilla have a D-shaped cross-section. The maxillary and dentary teeth are elongated, only recurving near the top, with perpendicular denticles on both edges. Their bases are circular in cross-section; the top of the tooth crown is more flattened.Aviatyrannis was in 2003 by Rauhut placed in the Tyrannosauroidea, in a basal position. Aviatyrannis is one of the oldest tyrannosauroids ever found, the oldest being Proceratosaurus (or, possibly, Iliosuchus).

Bagaraatan

Bagaraatan (/'ba-ɣa-raa-tan/ meaning 'small' baɣa + 'carnivorous animal, beast of prey' araatan in Mongolian) is 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 to 4 metres (9.8 to 13 ft) in length.

The type species, B. ostromi, was described by Osmolska in 1996. The post-cranial (ZPAL MgD-I/108) skeleton has been described as "bird-like", while the skull exhibits features of several different theropod groups.

Bahariasaurus

Bahariasaurus (meaning "Bahariya lizard") is a genus of theropod dinosaur found in the Bahariya Formation in El-Waha el-Bahariya or Bahariya (Arabic: الواحة البحرية meaning the "northern oasis") oasis in Egypt, the Farak Formation of Niger, and Kem Kem Beds of North Africa, which date to the late Cretaceous Period, (Cenomanian age), about 95 million years ago. It was a huge theropod, in the same size range as Tyrannosaurus and the contemporary genus Carcharodontosaurus.The type species, B. ingens, was described by Ernst Stromer in 1934, though the type specimen was destroyed during World War II. The exact placement of Bahariasaurus is uncertain, although it has been variously assigned to several theropod groups, including Carcharodontosauridae (by Rauhut in 1995) and Tyrannosauroidea (by Chure in 2000). It is potentially synonymous with Deltadromeus, another theropod from the early Late Cretaceous of North Africa, this would possibly make it the largest ceratosaur. More specimens would be needed to more accurately classify it, and to determine its relationship to Deltadromeus.In 2016 the description and analysis of Aoniraptor, Bahariasaurus was found along with Aoniraptor and Deltadromeus to probably form a still poorly known clade of megaraptoran tyrannosauroids different from the Megaraptoridae.

Coeluridae

Coeluridae is a historically unnatural group of generally small, carnivorous dinosaurs from the late Jurassic Period. For many years, any small Jurassic or Cretaceous theropod that did not belong to one of the more specialized families recognized at the time was classified with the coelurids, creating a confusing array of 'coelurid' theropods that were not closely related. Although they have been traditionally included in this family, there is no evidence that any of these primitive coelurosaurs form a natural group with Coelurus, the namesake of Coeluridae, to the exclusion of other traditional coelurosaur groups.

Coelurosauria

Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.

Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrannosaurs, ornithomimosaurs, and maniraptorans; Maniraptora includes birds, the only dinosaur group alive today.Most feathered dinosaurs discovered so far have been coelurosaurs. Philip J. Currie considers it likely and probable that all coelurosaurs were feathered. In the past, Coelurosauria was used to refer to all small theropods, but this classification has since been abolished.

Dilong paradoxus

Dilong (帝龍, which means 'emperor dragon') is a genus of basal 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 126 million years ago.

Dryptosaurus

Dryptosaurus ( DRIP-toh-SOR-əs) is a genus of tyrannosauroid that lived approximately 67 million years ago during the latter part of the Cretaceous period in what is now New Jersey. Dryptosaurus was a large, bipedal, ground-dwelling carnivore, that could grow up to 7.5 m (25 ft) long. Although largely unknown now outside of academic circles, a famous painting of the genus by Charles R. Knight made it one of the more widely known dinosaurs of its time, in spite of its poor fossil record. First described by Edward Drinker Cope in 1866 and later renamed by Othniel C. Marsh in 1877, Dryptosaurus is among the first theropod dinosaurs known to science.

Eotyrannus

Eotyrannus (meaning "dawn tyrant") is 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. The remains (MIWG1997.550), consisting of assorted skull, axial skeleton and appendicular skeleton elements, from a juvenile or subadult, found in a plant debris clay bed, were described by Hutt et al. in early 2001. The etymology of the generic name refers to the animals classification as an early tyrannosaur or "tyrant lizard", while the specific name honors the discoverer of the fossil.

Itemirus

Itemirus is a genus of theropod dinosaur from the Turonian age of the Late Cretaceous period of Uzbekistan.

Megaraptora

Megaraptora is a clade of carnivorous theropod dinosaurs with elongated hand claws and controversial relations to other theropods.Megaraptorans are incompletely known, and no complete megaraptoran skeleton has been found. However, they still possessed a number of unique features. Their forelimbs were large and strongly built, and the ulna bone had a unique shape in members of the family Megaraptoridae, a subset of megaraptorans which excludes Fukuiraptor. The first two fingers were elongated, with massive curved claws, while the third finger was small. Megaraptoran skull material is very incomplete, but a juvenile Megaraptor described in 2014 preserved a portion of the snout, which was long and slender. Leg bones referred to megaraptorans were also quite slender and similar to those of coelurosaurs adapted for running. Although megaraptorans were thick-bodied theropods, their bones were heavily pneumatized, or filled with air pockets. The vertebrae, ribs, and the ilium bone of the hip were pneumatized to an extent which was very rare among theropods, only seen elsewhere in taxa such as Neovenator. Other characteristic features include opisthocoelous neck vertebrae and compsognathid-like teeth.The clade was originally named in 2010 as a subset of the family Neovenatoridae, a group of lightly-built allosauroids related to the massive carcharodontosaurids such as Giganotosaurus and Carcharodontosaurus. A 2013 phylogenetic analysis by Fernando Novas and his colleagues disagreed with this classification scheme, and instead argued that the megaraptorans evolved deep within Tyrannosauroidea, a superfamily of basal coelurosaurs including the famous Tyrannosaurus. Subsequent refinements to Novas's data and methodologies have supported a third position for the group, at the base of Coelurosauria among other controversial theropods such as Gualicho, but not within the Tyrannosauroidea. Regardless of their position, it is clear that megaraptorans experienced a large amount of convergent evolution with either Neovenator-like allosauroids or basal coelurosaurs.Megaraptorans were most diverse in the early Late Cretaceous of South America, particularly Patagonia. However, they had a widespread distribution. Fukuiraptor, the most basal ("primitive") known member of the group, lived in Japan. Megaraptoran material is also common in Australia, and the largest known predatory dinosaur from the continent, Australovenator, was a megaraptoran.

Proceratosauridae

Proceratosauridae is a family or clade of theropod dinosaurs from the Middle Jurassic to the Early Cretaceous.

Proceratosaurus

Proceratosaurus is a genus of small-sized (~3 metres (9.8 ft) long) carnivorous theropod dinosaur from the Middle Jurassic (Bathonian) of England. It was originally thought to be an ancestor of Ceratosaurus, due to the similar small crest on its snout. Now, however, it is considered a coelurosaur, specifically one of the earliest known members of the clade Tyrannosauroidea.The type specimen is held in the Natural History Museum in London and was recovered in 1910 at Minchinhampton while excavating for a reservoir.

Santanaraptor

Santanaraptor (meaning "Santana Formation thief") is a genus of tyrannosauroid dinosaur that lived in South America during the Early Cretaceous (late Aptian-early Albian), about 112 million years ago.

Stokesosaurus

Stokesosaurus (meaning "Stokes' lizard") is a genus of small (around 3 to 4 meters (10 to 13 ft) in length), carnivorous early tyrannosauroid theropod dinosaurs from the late Jurassic period of Utah, United States.

Thomas R. Holtz Jr.

Thomas Richard Holtz Jr., Ph.D. is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorphology, and locomotion of terrestrial predators, especially on tyrannosaurids and other theropod dinosaurs. He wrote the book Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages and is the author or co-author of the chapters "Saurischia", "Basal Tetanurae", and "Tyrannosauroidea" in the second edition of The Dinosauria. He has also been consulted as a scientific advisor for the Walking With Dinosaurs BBC series as well as the Discovery special When Dinosaurs Roamed America, and has appeared in numerous documentaries focused on prehistoric life, such as Jurassic Fight Club on History and Monsters Resurrected on Discovery.Holtz is also the director of the Science and Global Change Program within the College Park Scholars living-learning community at the University of Maryland, College Park.

Xiongguanlong

Xiongguanlong ("Grand Pass dragon") 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 city of Jiayuguan, a city in northwestern China. The specific name is derived from bai mo, "white ghost", after the "white ghost castle", a rock formation near the fossil site. The fossils include a skull, vertebrae, a right ilium and the right femur. The rocks it was found in are from the Aptian to Albian stages of the Cretaceous, between 125 and 100 million years ago.

Yutyrannus

Yutyrannus (meaning "feathered tyrant") is a genus of tyrannosauroid dinosaurs which contains a single known species, Yutyrannus huali. This species lived during the early Cretaceous period in what is now northeastern China. Three fossils of Yutyrannus huali—all found in the rock beds of Liaoning Province—are currently the largest-known dinosaur specimens that preserve direct evidence of feathers.

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