Жоғалған динозаврлар суперотряды: Тираннозаврлар эволюциясы

Extinct superfamily of dinosaurs

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 and Asia, with fragmentary remains possibly attributable to tyrannosaurs also known from 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 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 in length, and a fully grown Guanlong measured long. Teeth from Lower Cretaceous rocks (140 to 136 million years old) of Hyogo, Japan, appear to have come from an approximately long animal, possibly indicating an early size increase in the lineage. An immature Eotyrannus was over in length, and a subadult Appalachiosaurus was estimated at more than long,

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, 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. 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. 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. 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. 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. This structure was shared by derived ornithomimids, troodontids and caenagnathids, but was not present in basal tyrannosauroids like Dilong paradoxus, indicating convergent evolution. 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. 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. The Sereno definition was adopted in a 2010 review. However, other authors disputed the placement of megaraptorans within Tyrannosauroidea, 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.

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. Within this group, the allosaurids 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. 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. A 2007 analysis found the family Coeluridae, including the Late Jurassic North American genera Coelurus and Tanycolagreus, to be the sister group of Tyrannosauroidea. Other early taxa include Stokesosaurus and Aviatyrannis, known from far less complete material. Alectrosaurus, a poorly known genus from Mongolia, is definitely a tyrannosauroid but its exact relationships are unclear. 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.

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. 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. This reanalysis of phylogenetic relationships of tyrannosauroids in Appalachia has brought the rediscovery of the clade Dryptosauridae due to the similarities of the metatarsals II and IV compared to the same bones in Dryptosaurus holotype. and the Tetori Group of Japan. 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, as well as formations in Kazakhstan and Tajikistan; two genera, Timurlengia and Xiongguanlong, have been found in Asia, while the Brazilian Santanaraptor may belong to this group. 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. Non tyrannosaurid tyrannosauroids like Alectrosaurus and possibly Bagaraatan were contemporaneous with tyrannosaurids in Asia, while they are absent from western North America. However, a response suggested that critical tyrannosauroid characters were absent from the fossil. 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.

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. 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. 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.

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. 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 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. 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, Possibly, 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. However, other paleontologists argue that taphonomy is the possible cause of the lack of filamentous structures in tyrannosaurid fossils.

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.