Tyrannosauroidea

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Tyrannosauroids
Temporal range:
Ma
Replica skeletons of
Yutyrannus huali
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Coelurosauria
Clade:
Tyrannoraptora
Superfamily: †Tyrannosauroidea
Osborn, 1906 (vide Walker, 1964)
Type species
†
Tyrannosaurus rex

Osborn, 1905
Subgroups

Tyrannosauroidea (meaning 'tyrant lizard forms') is a

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 and Asia, with fragmentary remains possibly attributable to tyrannosaurs also known from South America and Australia.

Tyrannosauroids were

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.

Description

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.

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 feet) in length,[5] and a subadult Appalachiosaurus was estimated at more than 6 meters (20 feet) long,[1] indicating that both genera reached larger sizes. The Late Cretaceous tyrannosaurids ranged from the 9 meters (30 feet) Albertosaurus and Gorgosaurus to Tyrannosaurus, which exceeded 12 meters (39 feet) in length and may have weighed more than 6,400 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]

Skull and neck of Daspletosaurus, from the Field Museum of Natural History in Chicago.

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

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.

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

caenagnathids,[14] but was not present in basal tyrannosauroids like Dilong paradoxus, indicating convergent evolution.[2]

Classification

Skull of Proceratosaurus, a proceratosaurid tyrannosauroid from the Middle Jurassic of England.

Tyrannosaurus was named by

paleontologist Alick Walker.[16] The suffix -oidea, commonly used in the name of animal superfamilies, is derived from the Greek ειδος eidos ('form').[17]

Scientists have commonly understood Tyrannosauroidea to include the tyrannosaurids and their immediate ancestors.

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

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

sister group of Tyrannosauroidea.[32]

The most basal tyrannosauroid known from complete skeletal remains is Guanlong, a representative of the family

carnosaur today.[34][41] 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][41]

Below on the left is a cladogram of Tyrannosauroidea from a 2022 study by Darren Naish and Andrea Cau on the genus Eotyrannus, and on the right is a cladogram of Eutyrannosauria from a 2020 study by Jared T. Voris and colleagues on the genus Thanatotheristes:[42][43]

Tyrannosauroidea
Eutyrannosauria

Dryptosaurus aquilunguis

Appalachiosaurus montgomeriensis

Bistahieversor sealeyi

Tyrannosauridae
Albertosaurinae

Gorgosaurus libratus

Albertosaurus sarcophagus

Tyrannosaurinae
Alioramini

Qianzhousaurus sinensis

Alioramus remotus

Alioramus altai

Teratophoneus curriei

Dynamoterror dynastes

Lythronax argestes

Nanuqsaurus hoglundi

Daspletosaurini

Thanatotheristes degrootorum

Daspletosaurus torosus

Daspletosaurus horneri

Zhuchengtyrannus magnus

Tarbosaurus bataar

Tyrannosaurus rex

Phylogeography

In 2018 authors Rafael Delcourt and Orlando Nelson Grillo published a phylogenetic analysis of Tyrannosauroidea which incorporated taxa from the ancient continent of Gondwana (which today consists of the southern hemisphere), such as Santanaraptor and Timimus, whose placement in the group has been controversial.[44] They have found that not only Santanaraptor and Timimus were placed as tyrannosaurs more derived than Dilong, but they have found in their analysis that tyrannosauroids were widespread in Laurasia and Gondwana since the Middle Jurassic.[44] They have proposed new subclade names for Tyrannosaurioidea. The first is Pantyrannosauria referring to all non-proceratosaurid members of the group, while Eutyrannosauria for larger tyrannosaur taxa found in the northern hemisphere such as Dryptosaurus, Appalachiosaurus, Bistahieversor, and Tyrannosauridae.[44] Below is their phylogeographic tree they have recovered, in which displays the phylogenetic relationships of the taxa as well as the continents those taxa have been found.[44]

Tyrannosauroidea
Proceratosauridae

Guanlong wucaii

Proceratosaurus bradleyi

Kileskus aristotocus

Sinotyrannus kazuoensis

Yutyrannus huali

Pantyrannosauria

Aviatyrannis jurassica

Dilong paradoxus

Santanaraptor placidus

Timimus hermani

Stokesosaurus clevelandi

Juratyrant langhami

Eotyrannus lengi

Xiongguanlong baimoensis

NMV P186046 ("Australian tyrannosaur")

Alectrosaurus olseni

Timurlengia euotica

Eutyrannosauria

Dryptosaurus aquilunguis

Appalachiosaurus montgomeriensis

Bistahieversor sealeyi

Tyrannosauridae
Albertosaurinae

Gorgosaurus libratus

Albertosaurus sarcophagus

Tyrannosaurinae
Alioramini

Qianzhousaurus sinensis

Alioramus remotus

Alioramus altai

Nanuqsaurus hoglundi

Teratophoneus curriei

Lythronax argestes

Daspletosaurus torosus

Daspletosaurus horneri

Zhuchengtyrannus magnus

Tarbosaurus bataar

Tyrannosaurus rex

In 2021, Chase Brownstein published a research article based on more thorough descriptions of tyrannosauroid

Dryptosauridae due to the similarities of the metatarsals II and IV compared to the same bones in Dryptosaurus holotype.[45] However the Merchantville taxon was able to still be different enough to separate it on the genus level from Dryptosaurus. In the phylogentic tree constructed Dryptosauridae is found to be a valid family of non tyrannosaurid eutyrannosaur. It currently sits in a polytomy with the Iren Dabasu taxon and more basal eutryannosaurs.[45]

Distribution

The tyrannosauroids lived on the supercontinent Laurasia, which split from Gondwana in the Middle Jurassic. The earliest recognized tyrannosauroids lived in the Middle Jurassic, represented by the proceratosaurids Kileskus from the Western Siberia and Proceratosaurus from Great Britain. Upper Jurassic tyrannosauroids include Guanlong from China, Stokesosaurus from the western United States and Aviatyrannis and Juratyrant from Europe.

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[46] and the Tetori Group of Japan.[47]

The Middle Cretaceous record of Tyrannosauroidea is rather patchy. Teeth and indeterminate postcrania of this interval are known from the Cenomanian-age

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.[52] 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]

Victoria.[53] However, a response suggested that critical tyrannosauroid characters were absent from the fossil.[54] The Australian taxon Timimus, known from a femur, and the Brazilian Santanaraptor, known from a partial juvenile skeleton, have also been suggested to be tyrannosaurs.[44] However, these placements have been considered questionable, with the supposed tyrannosauroid characters of Santanaraptor being widely distributed within Coelurosauria, in other characters having similarities to noasaurids.[55]

Paleobiology

Facial tissue

A conference paper by Tracy Ford states that there was rough bone texture on the skulls of theropods and higher foramina frequency than lepidosaurs and mammals which would be evidential for a sensitive snout for theropods.[56][57] A study in 2017 study about a new tyrannosaurid named Daspletosaurus horneri was published in the journal Scientific Reports. Paleontologist Thomas Carr analyzed the craniofacial texture of Daspletosaurus horneri and observed a hummocky rugosity which compared to crocodilian skulls and suggesting Daspletosaurus horneri including all tyrannosaurids have flat sensory scales. The subordinate regions were analyzed to have cornified epidermis.[58] However, a 2018 presentation has an alternative interpretation. Crocodilians don't have flat sensory scales but rather cracked cornified epidermis due to growth. The hummocky rugosity in the skulls of lepidosaurs have correlation with scales which this bone texture is also present in tyrannosaurid skulls. The foramina frequency in theropod skulls does not exceed 50 foramina which shows that theropods had lips. It's been proposed that lips are a primitive trait in tetrapods and the soft tissue present in crocodilians are a derived trait because of aquatic or semiaquatic adaptations.[59][60][61][62][63]

Body integument

Long

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.[68]

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

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 scientific publication by Phil Bell and colleagues in 2017 show that tyrannosaurids such as Gorgosaurus, Tarbosaurus, Albertosaurus, Daspletosaurus, and Tyrannosaurus had scales. The Bell et al. 2017 paper notes that the scale-like integument on bird feet were actually secondarily derived feathers according to paleontological and evolutionary developmental evidence so they hypothesize that the scaly skin preserved on some tyrannosaurid specimens might be secondarily derived from filamentous appendages like on Yutyrannus although strong evidence is needed to support this hypothesis.[70][71][72] However, other paleontologists argue that taphonomy is the possible cause of the lack of filamentous structures in tyrannosaurid fossils.[73]

Head crests

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

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.[74]

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External links
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