User:Pengyuli2019/sandbox

Pengyuli2019/sandbox Temporal range: Middle Jurassic–Late Cretaceous, Possible Late Maastrichtian record
Allosaurus fragilis skull, San Diego Natural History Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Clade:	†Carnosauria
Superfamily:	†Allosauroidea Marsh, 1878
Type species
†Allosaurus fragilis Marsh, 1877
Subgroups
†Erectopus †Metriacanthosauridae †Allosauria †Allosauridae †Carcharodontosauria †Datanglong †Carcharodontosauridae †Neovenatoridae †Megaraptora?

Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids were the first giant taxa, with weights exceeding 2 tons, of the theropods. They, along with members of the clade Megalosauroidea, were large predators that were active during the Middle Jurassic to Late Cretaceous periods. The most famous and best understood allosauroid is the North American genus Allosaurus.

The oldest-known allosauroid, Shidaisaurus jinae, appeared in the early Middle Jurassic (probably Bajocian stage) of China. The last known definitive surviving members of the group died out around 93 million years ago in Asia (Shaochilong) and South America (Mapusaurus), though the megaraptorans may belong to the group as well. Additional, but highly fragmentary, remains probably belonging to carcharodontosaurids have been found from the Late Maastrichtian (70-66 Ma ago) in Brazil.

Allosauroids had long, narrow skulls, large orbits, three-fingered hands, and usually had "horns" or ornamental crests on their heads. Although allosauroids vary in size, they maintain a similar center of mass and hip position on their body. Allosauroids also exhibit reptilian-style immune systems, based off of examining injuries and infections on their bones. It is possible that allosauroids were social animals, as many remains of allosauroids have been found in close proximity to each other.

Classification

Allosauroidea skull comparison

The cladogram of the classification of Allosauroidea

The clade Allosauroidea was originally proposed by Phil Currie and Zhao (1993; p. 2079), and later used as an undefined stem-based taxon by Paul Sereno (1997). Sereno (1998; p. 64) was the first to provide a stem-based definition for the Allosauroidea, defining the clade as "All neotetanurans closer to Allosaurus than to Neornithes." Kevin Padian (2007) used a node-based definition, defined the Allosauroidea as Allosaurus, Sinraptor, their most recent common ancestor, and all of its descendants. Thomas R. Holtz and colleagues (2004; p. 100) and Phil Currie and Ken Carpenter (2000), among others, have followed this node-based definition. Of the allosauroids, sinraptorids make up the most basal group.

However, in some analyses (such as Currie & Carpenter, 2000), the placement of the carcharodontosaurids relative to the allosaurids and sinraptorids is uncertain, and therefore it is uncertain whether or not the carcharodontosaurids are allosauroids (Currie & Carpenter, 2000).

The cladogram presented here is simplified after the 2012 analysis by Carrano, Benson and Sampson after the exclusion of three "wildcard" taxa Poekilopleuron, Xuanhanosaurus and Streptospondylus.

Description

Allosauroids share certain distinctive features, one of which is a triangular-shaped pubic boot. Allosauroids have 3 fingers per hand, with the second and third digit being approximately equal in length. The femur is larger than the tibia. Another defining feature of allosauroids is that the chevron bases on their tails have anterior and posterior bone growth. The body of allosauroids can reach up to 7 to 10 meters in length; the length of the body from the tail to the hip is between 54% and 62% of the total body length, and the length of the body from the head to the hip is between 38% and 46% of the total body length. Allosauroids scaled their limbs relative to their body in a way similar to how other large therapods, like the tyrannosaurids, did.

Allosauroids maintain a similar center of mass across all sizes, which is found to be between 37% and 58% of the femoral length anterior to the hip. Other similarities across all allosauroids include the structure of their hind limb and pelvis. The pelvis in particular is thought to be designed to reduce stress regardless of body size. In particular, the way the femur is inclined reduces the bending and torsion stress. Furthermore, like other animals with tails, allosauroids possess a caudofemoralis longus (CFL) muscle that allow them to flex theirs. Larger allosauroids are found to have a lower CFL muscle-to-body-mass proportion that smaller allosauroids.

Allosauroid skulls are about 2.5 to 3 times longer as they are tall. Their narrow skull along with their serrated teeth allow allosauroids to better slice flesh off of their prey. From analyzing the skull of different allosauroids, the volume of the cranial vault ranges between 95 milliliters in Sinraptor to 250 milliliters in Giganotosaurus. Allosauroid teeth are flat and have equally-sized denticles on both edges. The flat side of the tooth face the sides of the skull, while the edges align on the same plane as the skull.

Paleobiology

Multiple severe injuries have been found on allosauroid remains, but only a few of those injuries show infection. For those injuries that did become infected, the infections were usually local to the site of the injury, implying that the allosauroid immune response was able to quickly stop any infection from spreading to the rest of the body. This type of immune response is similar to modern reptilian immune responses; reptiles secrete fibrin near infected areas and localize the infection before it can spread via the bloodstream.

The injuries were also found to be mostly healed. This healing may indicate that allosauroids had an intermediate metabolic rate, similar to non-avian reptiles, which means they require less nutrients in order to survive. A lower nutrient requirement means allosauroids do not need to undertake frequent hunts, which lowers their risk of sustaining traumatic injuries.

Paleobiogeography

Allosauroids first appeared in the Middle Jurassic period and were the first giant taxa (weighing more than 2 tons) in theropod history. Along with members of the superfamily Megalosauroidea, allosauroids were the large predators that occupied the Middle Jurassic to the early Late Cretaceous periods. Allosauroids have been found in North America, South America, Europe, Africa, and Asia. Specifically, a world-wide dispersal of carcharodontosauroids likely happened in the Early Cretaceous. It has been hypothesized that the dispersal involved Italy’s Apulia region (the “heel” of the Italian peninsula), which was connected to Africa by a land bridge during the Early Cretaceous period; various dinosaur footprints found in Apulia support this theory. Allosauroids were present in both the northern and southern continents during the Jurassic and Early Cretaceous, but they were later displaced by the tyrannosauroids in North America and Asia during the Late Cretaceous. This is likely due to regional extinction events, which differentiated many dinosaurs in the Late Cretaceous.

Cryolophosaurus is the oldest allosauroid tetanuran and was discovered in Antarctica. Upon examination, Cryolophosaurus’ body structure is very similar to those of other allosauroids found in other Upper Jurassic rocks. Neovenator salerii, found in England, was the first allosauroid attributed to Europe. Allosauroid remains found in Tanzania and Australia have confirmed that allosauroids survived into the Early Cretaceous.

CPT-1980

CPT-1980 is the museum catalog number for an isolated, 9.83 centimetres (3.87 in), allosauroid tooth crown currently housed at the Museo Fundación Conjunto Paleontológico de Teruel. In 2009, the tooth was compared to another allosauroid tooth from Portugal that measured 12.7 centimetres (5.0 in). Analysis led to the conclusion that CPT-1980 is the largest theropod tooth ever discovered in Spain. This tooth was discovered by locals near Riodeva, Teruel in the Villar del Arzobispo Formation, more specifically known as RD-39. The rocks have been dated to the Tithonian-Berriasian stages (Late Jurassic-Early Cretaceous).