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| Ceratosaurs | |
|---|---|
 | |
| Six ceratosaurs (top left to bottom right):Rugops,Elaphrosaurus,Majungasaurus,Carnotaurus,Ceratosaurus,Berthasaura | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Neotheropoda |
| Clade: | Averostra |
| Clade: | †Ceratosauria Marsh, 1884 |
| Type species | |
| †Ceratosaurus nasicornis Marsh, 1884 | |
| Subgroups | |
Ceratosaurs are members of the cladeCeratosauria, a group ofdinosaurs defined as alltheropods sharing a more recent common ancestor withCeratosaurus than with birds. The oldest known ceratosaur,Saltriovenator, dates to the earliest part of the Jurassic, around 199 million years ago. Ceratosauria includes three major clades: Ceratosauridae,Noasauridae, andAbelisauridae, found primarily (though not exclusively) in theSouthern Hemisphere. Originally, Ceratosauria included the above dinosaurs plus the Late Triassic to Early JurassicCoelophysoidea andDilophosauridae, implying a much earlier divergence of ceratosaurs from other theropods. However, most recent studies have shown that coelophysoids and dilophosaurids do not form anatural group with other ceratosaurs, and are excluded from this group.[1]
Ceratosauria derives its names from the type species,Ceratosaurus nasicornis, described byO.C. Marsh in 1884. A moderately large predator from the Late Jurassic,Ceratosaurus nasicornis, was the first ceratosaur to be discovered. Ceratosaurs are generally moderately large in size, with some exceptions like the largerCarnotaurus and the significantly smaller noasaurs. The major defining characteristics of Ceratosauria include a robust skull with increased ornamentation or height and a shortening of the arms.[2] Both of these characteristics are generally accentuated in later members of the group, such as theabelisaurs, whereas more basal species such asC. nasicornis appear more similar to other basaltheropods. The highly fragmented nature of the ceratosaur fossil record means that the characteristics, relationships, and early history of Ceratosauria remain mysterious and highly debated.
Ceratosauria was first described byO.C. Marsh in theAmerican Journal of Science in 1884. Writing about the newly discoveredC. nasicornis, he noted the similarities between the firmly united metatarsals ofC. nasicornis and those ofArchaeopteryx. SinceC. nasicornis was the only other dinosaur discovered at the time to share this trait, Marsh concluded that Ceratosauria must be placed very nearArchaeopteryx and its related groups.[3] Marsh also named the familyCeratosauridae in 1884 to containC. nasicornis. Since then, a number of other species have been referred to this family, mainly from thegenusCeratosaurus.
The idea of the Ceratosauria would be contested by Marsh's rival,Edward Drinker Cope. Cope argued that the taxon was invalid.[4] The idea of the Ceratosauria would regain some support more than thirty years later when Gilmore argued in its favor in 1920. Despite Gilmore's support, few species were added to the group following World War I, and little emphasis was placed on it. In fact, the scientific community's most common interaction with Ceratosauria throughout much of the 20th century was the disputation of its existence, performed by the likes ofRomer,Lapparent,Lavocat,Colbert, andCharig amongst others.
Ceratosauria's fortune changed in 1986 whenJacques Gauthier, in an attempt to clarify the evolution of birds, grouped the majority of theropods into either Ceratosauria orTetanurae. In Ceratosauria, he placed the ceratosaurs andcoelophysoids.[5] Gauthier's paper brought Ceratosauria's use back in vogue, and by the early 1990s,Abelisauridae had also been included under Ceratosauria. The triumvirate model of ceratosaurs, coelophysoids, and abelisaurids would go unchallenged until the early 2000s. Beginning at the turn of the millennium, a large number of paleontologists began excluding coelophysoids from Ceratosauria. This view is now widely held thanks to several similarities between Ceratosauria and Tetanurae not found in coelophysoids.
Most paleontologists have postulated that Ceratosauria split off from other theropods in the Late Triassic or earliest Jurassic. Despite this, no ceratosaurs have been discovered prior to the Early Jurassic, and even in the Middle Jurassic, species are sparse. Many scientists, such as Carrano and Sampson, have postulated the lack of specimens is due to a poor fossil record, rather than an indictment on the abundance of ceratosaurs at the time. A similarly large gap of specimens exist in the lower Cretaceous, particularly forAbelisauridae. More recent discoveries have resulted in varying phylogenetic results concerning the relationships betweenElaphrosaurus and the derivedCretaceousnoasaurids. The precise relationship betweenCeratosaurus and theabelisaurids is also not clearly resolved.[6][7][2]
Currently, most paleontologists agree that Ceratosauria contains a slightly more exclusive clade,Neoceratosauria, which contains the groupsCeratosauridae andAbelisauroidea, with some variance as to which taxa are placed into basal polytomy.[2][8] Abelisauroidea is further divided into theAbelisauridae andNoasauridae, with Abelisauridae, includingCarnotaurinae. Recently, Rauhut and Carrano have placed Elaphrosaurinae inside Noasauridae while simultaneously moving the previous noasaurs into Noasaurinae.[8] Into their new Noasauridae, they have uniquely includedDeltadromeus andLimusaurus.
It is difficult to discern possiblesynapomorphies of Ceratosauridae fromautapomorphies ofCeratosaurus because the remains of the relatedGenyodectes are so fragmentary; e.g.Ceratosaurus is different from other ceratosaurians by the very prominenthorn on its snout;Genyodectes, however, was not found with a completeskull; whether it had a horn is unknown, so it cannot establish that the horn was a shared derived feature of the group. However, due to the shared similarities between the teeth of the two genera, synapomorphies have been recognized in the teeth. The synapomorphies that do exist include: overlap of the second and third premaxillary alveoli in palatal view, largest crown in subadults/adults higher than six centimeters, subquadrangular mesial denticles at two-thirds of the crown in lateral teeth.[9] Currently the only generally-recognized ceratosaurid species outside the genusCeratosaurus isGenyodectes from theCretaceous orPatagonia. The taxaEoabelisaurus andOstafrikasaurus are also probable ceratosaurs, but it is unknown if they belong to Ceratosauridae.[10] Delcourt (2018) defined Ceratosauridae as "the most inclusive clade containingCeratosaurus nasicornis but notCarnotaurus sastrei".[11]
Abelisauroidea is a diverse superfamily of ceratosaurians and the sister taxon of Ceratosauridae. It is typically regarded as aCretaceous group, though the earliestabelisaurid remains are known from theMiddle Jurassic ofArgentina (classified as the speciesEoabelisaurus mefi) and possiblyMadagascar (fragmentary remains of an unnamed species). Possibleabelisaurid remains (an isolated lefttibia, rightfemur, and right tibia) were also discovered inLate JurassicTendaguru Beds inTanzania.
Abelisauroids flourished in theSouthern hemisphere during theCretaceous period, but their origins can be traced back to at least theMiddle Jurassic, when they had a more global distribution (the earliest known abelisauroid remains come fromAustralian andSouth American deposits dated to about 170 million years ago).[12] By the Cretaceous period, abelisauroids had apparently become extinct in Asia and North America, possibly due to competition fromtyrannosauroids. However, advanced abelisauroids of the family Abelisauridae persisted in the southern continents until theCretaceous–Paleogene extinction event 66 million years ago.[13]
In an assessment of the phylogenetic position ofEoabelisaurus, the analysis found it as the most basal member of theAbelisauridae. Abelisaurid synapomorphies include the laterally covered lacrimal antorbital fossa, broad cervical prespinal fossae, anteroposteriorly short anterior caudal neural spines, absence of a ventral groove in the anterior caudals, presence of rudimentary centrodiapophyseal laminae in the anterior mid-caudals, reduced distal ginglymus in the manual phalanges, and the presence of a flexor depression in the pedalunguals. Alternative phylogenetic placements ofEoabelisaurus are significantly suboptimal, except for a slightly more basal position.[14] Noasaurids had longer arms than their relatives the abelisaurids, whose arms were tiny and diminished. Although by no means as large or specialized as the arms of advanced bird-like theropods,noasaurid arms were nevertheless capable of movement and use, possibly even for hunting in large-clawed genera such asNoasaurus. Some genera such asLimusaurus did have somewhat reduced arms and hands, but far from the extent thatabelisaurids acquired.Noasaurids were also nimble and lightly built, with feet showing adaptations for running such as a long central foot bone. Noasaurids varied in size, from the smallVelocisaurus under 5 feet (1.5 meters) long, to much larger genera such asElaphrosaurus andDeltadromeus, which were more than 20 feet (6.1 meters) in length.[15]
The oldest known ceratosaur currently described isSaltriovenator zanellai which is dated to the EarlySinemurian, 199-197 Ma.[16] The origin of Ceratosauria could have been in Northern Pangea whereSaltriovenator, its close relativeBerberosaurus, andCarmelopodus footprints have been found.
The following family tree illustrates a synthesis of the relationships of the majortheropod groups based on various studies conducted in the 2010s and demonstrates the position of Ceratosauria within theropods.[17]
The followingcladogram shows the internal relationships within Ceratosauria following an analysis by Diego Pol and Oliver W. M. Rauhut, 2012.[2]
| Ceratosauria | |
A different conclusion was reached in a 2017 paper onLimusaurus ontogeny. Unlike other analyses,Noasauridae was placed more basal thanCeratosaurus, with the latter being withinAbelisauridae by definition.[18] This was later expanded on in a 2018 paper on ceratosaur paleobiology, which named a new clade Etrigansauria, which contained the families Abelisauridae and Ceratosauridae.[7] The following cladogram is a consensus tree of the latest phylogenies shown in the paper.
| Ceratosauroidea |
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Similar results were shown by the phylogenetic analysis from the describers ofAlpkarakush in 2024, where noasaurids were recovered outside a polytomy of ceratosaurids and abelisaurids.[19]
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Some of the defining characteristics of Ceratosauria include an increase in height and ornamentation of the skull, as well as a shortening of the forelimbs. Likewise, ceratosaurs fused their ilium, ischium, and pubis together, as well as the astragalus and calcaneum.[4] For less derived members of the group, such asC. nasicornis, traits such as raising of the skull and shortening of the forelimbs were not as noticeable. The skull ofC. nasicornis was rather similar to the basaltheropod mold, with a distinguishing nasal crest to go along with lacrimal crests similar to the contemporaryAllosaurus.C. nasicornis had larger teeth thanAllosaurus, and some paleontologists postulate that it would have had a difficult time attacking larger prey. Abelisaurids, however, carried many of these defining traits to their extremes. Most abelisaurids had largely shortened forelimbs, withCarnotaurus having shrunk them further than any large theropod.[20] After analyzing the features of the newly discoveredRugops primus, Paul Sereno has postulated that many of these abelisaurid features may lend themselves to scavenging.[21] Despite the huge reduction in size, no taxa in Ceratosauria ever lost a digit or any critical elements of the forelimb. Some joint variation has also been observed in Ceratosauria, and it has been postulated that they may have had better shoulder mobility than other large theropods.[1]
There are two known types ofCeratosaurusteeth: one with longitudinal ridges and the other with veinedenamel. Both types of teeth have crowns with a teardrop-shaped cross section and carinae running up the middle. The cross section of the tooth's base depends on the position of the tooth in the mouth with front teeth having less symmetric cross sections.
Completeskeletons have been described only for the most advancedabelisaurids (such asCarnotaurus andAucasaurus), making the establishment of defining features of the skeleton for the family as a whole more difficult. However, most are known from at least some skull bones, so known shared features come mainly from the skull. Many abelisauridskull features are shared withcarcharodontosaurids.[22] These shared features, along with the fact thatAbelisauridae seem to have replacedCarcharodontosauridae inSouth America, has led to suggestions that the two groups were related.Noasaurids were considered to be distinctive abelisauroids with a peculiar "sickle claw" on the second toe of the foot, convergently developed with that ofdeinonychosaurians. Amongnoasaurids, the Argentinean generaNoasaurus (Later Cretaceous) andLigabueino (Early Cretaceous) are known from incomplete specimens, including disarticulated non-ungual phalanges and inNoasaurus, a claw. A detailed overview of these elements indicates that the supposed raptorial claw of the second pedal digit actually belongs to the first or second finger of the manus, and the putative pedal non-ungual phalanges or both genera also pertain to the manus.[23]
Ceratosaurs appeared to have had a global population that diverged by the early Jurassic. However, they appear to have largely disappeared fromLaurasia in theCretaceous, with those few specimens that have been discovered having been possibly reintroduced fromGondwana.[24] No confirmed specimens of ceratosaurs in North America during the Cretaceous have been found.
Abelisaurids in particular had great success inGondwana, particularly in the Cretaceous. Some Gondwanan and Laurasian specimens have recently been found and dated to Late Jurassic, and possibly even the Middle Jurassic, greatly extending the abelisaurid timeline. Some paleontologists have postulated that a large desert may have kept abelisaurids locked in southern Gondwana until the late Jurassic.[2] Whether correlation or causation, it has been largely observed that late Cretaceous ceratosaurs were found less in areas dominated by basaltetanurans (Africa) orcoelurosaurs (North America and Asia). The below phylogeny follows a simplified cladogram of Hendrickx et al. (2015), limited to Ceratosauria.
| Ceratosauria | |
As with most theropods, ceratosaurs were carnivores—except for somenoasaurs likeLimusaurus andBerthasaura, which were omnivores or herbivores with toothless beaks.[25][26]Ceratosaurus has been argued to have eaten a large amount of fish and other aquatic creatures, though this has been disputed by many paleontologists.[27] Tooth marks on large animals such asAllosaurus indicate thatCeratosaurus likely utilized scavenging often.[28] The interesting jaws of theabelisaurids have drawn mixed dietary predictions. One study onCarnotaurus found that its bite, thanks to its shortened skull, was suited for hunting small prey, thanks to a quick, but relatively weak bite.[29] On the other hand, other groups of paleontologists have found that the bite ofCarnotaurus was relatively powerful, and more adept at hunting and wounding large prey.[30]
Others have postulated its skull was built for scavenging. The debate over the eating habits of ceratosaurs is quite active, particularly recently with the increase inabelisaur discoveries. Using three methods, namely a cladistic analysis performed on a dentition-based data matrix, and discriminant and cluster analyses conducted on a large dataset of theropod teeth measurements, three dental morphotypes which are confidently referred to abelisaurid theropods are identifiable. Whether the morphotypes represent different abelisaurid subclades or different positional entities within the jaw of the same abelisaurid species, is unknown. Such an identification, nevertheless, provides additional evidence of abelisaurids feeding on sauropod carcasses.[31]
Studies ofMajungasaurus indicate that it was a much slower-growing dinosaur than other theropods, taking nearly 20 years to reach adult size. Similar studies on other abelisaurid genera indicate that this slow maturation may have been a common trait to the whole of Abelisauridae.Noasaurines areLate Cretaceous noasaurids known exclusively from southern continents and islands such as South America, Madagascar, and India.Elaphrosaurines were lightly builttheropods, with small skulls and long necks and legs. IfLimusaurus is any indication, adult elaphrosaurines were completely toothless, and their mouths were probably edged with a horny beak. It is likely thatLimusaurus and otherelaphrosaurines were primarily herbivorous as adults, due to matureLimusaurus specimens preservinggastroliths and chemical signatures resembling those ofherbivorousdinosaurs.
Being found in theMorrison andTendaguru put the family Ceratosauridae in the presence of other large predators. In North America, it is likely that members of the family such asC. nasicornis competed withallosaurids (A. fragilis) for food, such assauropods common to the region at the time. InAfrica andEurope members also competed with other large predators for similar food sources. The presence ofC. nasicornis at theCleveland-Lloyd Dinosaur Quarry along with the remains of several allosaurids is a good indication of just how close members of this family and other predators coexisted.
Most abelisauroid ceratosaurs were found inMadagascar,Asia, or sometimes inAfrica.Abelisauridae thrived during theCretaceous period on the ancient southernsupercontinent ofGondwana, and today theirfossil remains are found on the modern continents of Africa andSouth America, as well as on theIndian subcontinent and the island of Madagascar. In Madagascar,Majungasaurus was discovered by FrenchpaleontologistCharles Depéret.Majungasaurus was the most common abelisauroid which we know. In South America, many abelisauroids such asSkorpiovenator,Quilmesaurus,Aucasarus,Ilokelesia, andPyconemosaurus are known.Kurupi itaata represents the first formally namedvertebrate of theMarília Formation (Bauru Group,Bauru Basin) and one of the few theropod records for theMaastrichtian of the Bauru Basin. Its abelisaurid affinities are well established based on the anatomy of thepelvis andanteriorcaudalvertebrae; however, closer relationships with other abelisaurids are still unclear. The specimens provide new information on abelisauroids, which are still poorly known in the Brazilian fossil record, and on the distribution of this group of theropod dinosaurs in South America.[32] These discoveries indicate that abelisauroids were the most common large predatory dinosaurs where they lived.[33]
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