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Carnosauria is an extinct group ofcarnivorous theropoddinosaurs that lived during theJurassic andCretaceous periods.
While Carnosauria was historically considered largely synonymous withAllosauroidea, some recent studies have revived Carnosauria asclade including both Allosauroidea andMegalosauroidea (which is sometimes recovered asparaphyletic with respect to Allosauroidea), and thus including the majority of non-coleurosaurian members of theropod cladeTetanurae.[1] Other researchers have found Allosauroidea and Megalosauroidea to be unrelated groups.[2]
Distinctive characteristics of carnosaurs include largeeye sockets, a long narrowskull and modifications of thelegs andpelvis such as the thigh (femur) being longer than the shin (tibia).[3]
Carnosaurs first appeared in the Middle Jurassic around174 million years ago, and the last definitive carnosaur familyCarcharodontosauridae became extinct in theTuronian epoch of the Late Cretaceous around90 million years ago. Some theropod remains, once suggested to be putative carcharodontosaurids from theMaastrichtian epoch (72–66 mya) in South America, were later reinterpreted as those of other theropod groups including theabelisaurids andmaniraptorans.[4][5] Over the recent years, a majority of researchers have increasingly classifiedmegaraptorans ascoelurosaurs.[6][7][8][9]
Carnosauria has traditionally been used as a dumping ground for all large theropods. Even non-dinosaurs, such as therauisuchianTeratosaurus, were once considered carnosaurs. However, analysis in the 1980s and 1990s revealed that other than size, the group shared very few characteristics, making itpolyphyletic. Most former carnosaurs (such as themegalosaurids, thespinosaurids, and theceratosaurs) werereclassified as more primitive theropods. Others (such as thetyrannosaurids) that were more closely related to birds were placed inCoelurosauria. Moderncladistic analysis defines Carnosauria as thosetetanurans sharing a more recent common ancestor withAllosaurus than with modern birds.[10]
Carnosaurs share certain distinctive features, one of which is a triangular-shapedpubic boot.[11] They also 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 carnosaurs is that thechevron bases on their tails have anterior and posterior bone growth.[12] The largest carnosaurs can reach up 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.[13] Carnosaurs scaled their limbs relative to their body in a way similar to how other large theropods, like thetyrannosaurids, did.[14] During the Cretaceous, some carnosaurs grew to sizes similar to those of the largest tyrannosaurids.[15] These large carnosaurs lived in the same time period as the other large theropods found in the upper Morrison and Tendaguru formations.[16]
Carnosaurs maintained a similarcenter 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 carnosaurs 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, carnosaurs possess acaudofemoralis longus (CFL) muscle that allowed them to flex theirs. Larger carnosaurs are found to have a lower CFL muscle-to-body-mass proportion that smaller carnosaurs.[13]
In addition to body similarities, most carnosaurs, especially most allosauroids are also united by certain skull features. Some of the defining ones include a smallermandibularfenestra, a shortquadrate bone, and a short connection between the braincase and the palate.[17] Allosauroid skulls are about 2.5 to 3 times longer as they are tall.[16] Their narrow skull along with their serrated teeth allow carnosaurs to better slice flesh off of their prey. Carnosaur teeth are flat and have equally-sizeddenticles 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.[18] From analyzing the skull of different carnosaurs, the volume of thecranial vault ranges between 95 milliliters inSinraptor to 250 milliliters inGiganotosaurus.[19]
Allosaurus andConcavenator preserve skin impressions showing theirintegument. InAllosaurus, skin impressions showing smallscales measuring 1-3 mm are known from the side of the torso and themandible. Another skin impression from the ventral side of the neck preserves broad scutate scales. An impression from the base of the tail preserves larger scales around 2 cm in diameter. However, it has been noted that these may besauropod scales due to their similarity and the fact that non-theropod remains were discovered associated with the tail of this particularAllosaurus specimen.[20]Concavenator preserves rectangular scutate scales on the underside of the tail, as well as scutate scales on the feet along with small scales. A series of knobs on theulna ofConcavenator have been interpreted by some authors as quill knobs theorized to have supported primitive quills;[21] however this interpretation has been questioned, and they have been suggested to represent traces of ligaments instead.[22]
Within Carnosauria, there is a slightly more exclusive clade,Allosauroidea. Theclade Allosauroidea was originally named byOthniel Charles Marsh, but it was given a formal definition byPhil Currie and Zhao, and later used as astem-based taxon byPaul Sereno in 1997.[24] Sereno was the first to provide a stem-based definition for the Allosauroidea in 1998, defining the clade as "All neotetanurans closer toAllosaurus than toNeornithes."[25]Kevin Padian used a node-based definition in his 2007 study which defined the Allosauroidea asAllosaurus,Sinraptor, theirmost recent common ancestor, and all of its descendants.Thomas R. Holtz and colleagues andPhil Currie andKen Carpenter, among others, have followed this node-based definition.[26][27] Depending on the study, Carnosauria and Allosauroidea are sometimes considered synonymous. In such cases, several researchers have elected to use Allosauroidea over Carnosauria.[16][28]
The following family tree illustrates the position of Carnosauria within Theropoda. It is a simplified version of the tree presented in a synthesis of the relationships of the major theropod groups based on various studies conducted in the 2010s.[29]
Thecladogram presented below illustrates the interrelationships between the four major groups (or families) of carnosaurs. It is a simplified version of the tree presented in the 2012 analysis by Carrano, Benson and Sampson after they excluded three "wildcard" taxaPoekilopleuron,Xuanhanosaurus, andStreptospondylus.[16]
| Allosauroidea |
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The composition of the clade Carnosauria has been controversial among scientists since at least2010. Different clades have been recovered by different authors, and a scientific consensus has yet to emerge.
One such clade isNeovenatoridae, a proposed clade ofcarcharodontosaurian carnosaurs uniting some primitive members of the group such asNeovenator with theMegaraptora, a group of theropods with controversial affinities. Other studies recover megaraptorans as basalcoelurosaurs unrelated to carcharodontosaurs. Other theropods with uncertain affinities such asGualicho,Chilantaisaurus andDeltadromeus are also sometimes included.[30][31]
Neovenatoridae, as formulated by these authors, containedNeovenator,Chilantaisaurus, and a newly named clade: Megaraptora. Megaraptora containedMegaraptor,Fukuiraptor,Orkoraptor,Aerosteon, andAustralovenator. These genera were allied with the other neovenatorids on the basis of several features spread out throughout the skeleton, particularly the large amount of pneumatization present. The pneumatic ilium ofAerosteon was particularly notable, asNeovenator was the only other taxon known to have that trait at the time. Neovenatorids were envisioned as the latest-surviving allosauroids, which were able to persist well into the Late Cretaceous due to their low profile and coelurosaur-like adaptations.[28] Later studies supported this hypothesis, such as Carrano, Benson & Sampson large study of tetanuran relationships in 2012,[32] and Zanno & Makovicky description of the newly discovered theropodSiats in 2013, which they placed within Megaraptora.Fukuiraptor andAustralovenator were consistently found to be close relatives of each other; this was also the case forAerosteon andMegaraptor.Orkoraptor was a"wildcard" taxon difficult to place with certainty.[33]
Phylogenetic studies conducted by Benson, Carrano and Brusatte (2010) and Carrano, Benson and Sampson (2012) recovered the groupMegaraptora and a few other taxa as members of the Neovenatoridae. This would make neovenatorids the latest-surviving allosauroids; at least one megaraptoran,Orkoraptor, lived near the end of theMesozoic era, dating to the earlyMaastrichtian stage of the latestCretaceous period, about 70 million years ago.[28][16]
The cladogram below follows a 2016 analysis by Sebastián Apesteguía, Nathan D. Smith, Rubén Juarez Valieri, and Peter J. Makovicky based on the dataset of Carranoet al. (2012).[34]
| Allosauroidea |
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Subsequent analyses have contradicted the above hypothesis. Novas and colleagues conducted an analysis in 2012 which found thatNeovenator was closely related to carcharodontosaurids, simultaneously foundMegaraptor and related genera to becoelurosaurs closely related totyrannosaurids.[35] However, Novaset al. subsequently found that megaraptorans lacked most of the key features in the hands of derived coelurosaurs includingGuanlong andDeinonychus. Instead, their hands retain a number of primitive characteristics seen in basal tetanurans such asAllosaurus. Nevertheless, there are still a number of other traits that support megaraptorans as members of the Coelurosauria.[36][37] Other taxa likeDeltadromeus andGualicho have been alternatively recovered as coelurosaurs ornoasauridceratosaurs.[34][38]
Several recent analyses do not find a relationship betweenNeovenator and megaraptorans, which suggests that the latter were not carnosaurs or allosauroids. As a result of these findings, and the fact thatNeovenator itself is the only uncontroversial neovenatorid, the family Neovenatoridae sees little use in recent publications.[39][37][38]
In 2019, Rauhut and Pol describedAsfaltovenator vialidadi, a basal allosauroid displaying a mosaic of primitive and derived features seen withinTetanurae. Their phylogenetic analysis found traditionalMegalosauroidea to represent a basalgrade of carnosaurs,paraphyletic with respect to Allosauroidea. Because the authors amended the definition of Allosauroidea to include all theropods that are closer toAllosaurus fragilis than to eitherMegalosaurus bucklandii or Neornithes, thePiatnitzkysauridae was found to fall within Allosauroidea. A cladogram displaying the relationships they recovered is shown below.[1]
| Carnosauria | |
The relationship between allosauroids and megalosauroids was also supported by a provisional analysis published byAndrea Cau in 2021. This publication is also the origin of the hypothesis that several "compsognathids" from Europe may have been juvenile carnosaurs. The results of this analysis differ from those of Rauhut and Pol in that Cau finds Megalosauroidea to bemonophyletic and the sister-taxon of Allosauroidea within Carnosauria. An abbreviated version of this phylogeny is shown below.[40]
In 2024, Andrea Cau published a paper which presented an analysis of theropod ontogeny which suggested that several theropods that were traditionally consideredcoelurosaurs may be juvenile allosauroids or megalosauroids. These includedAorun,Juravenator,Sciurumimus,Scipionyx, andCompsognathus. This hypothesis has not been universally accepted, and it notably conflicts with Cau's 2021 publication by finding Megalosauroidea as monophyletic and the sister taxon ofAvetheropoda, a grouping which includes both carnosaurs (or allosauroids) and coelurosaurs. Notably, this analysis also treats theabelisauroid genusKryptops as achimera and suggests that the postcranial remains of this taxon belong to a carnosaur (possiblySauroniops). An abbreviated version of the cladogram from that analysis is shown below.[38]
| Tetanurae |
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Multiple severe injuries have been found on allosauroid remains, which implies that allosauroids were frequently in dangerous situations and supports the hypothesis of an active, predatory lifestyle. Despite the multitude of injuries, only a few of those injuries show signs of infection. For those injuries that did become infected, the infections were usually local to the site of the injury, implying that the allosauroidimmune 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.[41]
The injuries were also found to be mostly healed. This healing may indicate that allosauroids had an intermediatemetabolic rate, similar to non-avian reptiles, which means they require fewer 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.[41]
Although the remains of other large theropods like tyrannosaurids bear evidence of fighting within their species and with other predators, the remains of allosauroids do not bear much evidence of injuries from theropod combat. Most notably, despite a good fossil record, allosauroid skulls lack the distinctive face-biting wounds that are common in tyrannosaurid skulls, leaving open the question of if allosauroids engaged in interspecies and intraspecies fighting.[42] Remains of the allosauroidMapusaurus are also often found in groups, which could imply the existence of social behavior.[43] While there are alternative explanations for the groupings, likepredator traps orhabitat reduction due to drought, the frequency of finding allosauroid remains in groups supports the social animal theory. As social animals, allosauroids would share the burden of hunting, allowing injured members of the pack to recover faster.[41]
Thepaleobiogeographical history of allosauroids closely follows the order thatPangaea separated into the modern continents.[44] By the Middle Jurassic period, tetanurans had spread to every continent and diverged into the allosauroids and the coelurosaurs.[15] 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 superfamilyMegalosauroidea, allosauroids were the apex predators that occupied the Middle Jurassic to the early Late Cretaceous periods.[45] Allosauroids have been found in North America, South America, Europe, Africa, and Asia.[44] A probable carcharodontosaurian specimen from the upperStrzelecki Group and theEumeralla Formation (Aptian-Albian) ofAustralia might potentially extend their known distribution.[46]
Specifically, a world-wide dispersal of carcharodontosaurids likely happened in the Early Cretaceous. It has been hypothesized that the dispersal involved Italy'sApulia region (the “heel” of the Italian peninsula), which was connected to Africa by aland bridge during the Early Cretaceous period; various dinosaur footprints found in Apulia support this theory.[23] 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, along with increased species isolation through the severing of land connections between the continents, differentiated many dinosaurs in the Late Cretaceous.[15]
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