Theropoda: Avetheropoda: Carcharodontosauridae

partial skeleton and skull, originally considered an Allosaurid. Later study showed this large animal to be very primitive carcharodontosaurid. It has a very distinctive puffin-like snout. Its discovery, and that of another very primitive contemporary carcharodontosaurian, Concavenator, from the Las Hoyas in Cuenca, Spain, relates the early evolutionary history of this Gondwanan group to the Early Cretaceous of Europe (Ortega et al 2010). Neovenator appears to be a good example of an animal at the evolutionary cross-roads, intermediate or transitional between Allosaurus, primitive Carcharodontosaurs, and Megaptora. This powerful animal would have played an allosaurus-like role in the Early Cretaceous of central Laurasia.

Kelmayisaurus is one of those fossils where a supposedly anomalous form known only from very fragmentary remains later turns pout to be part of an ordinary lineage of that time. It is based on parts of the upper and lower jaws (maxilla and dentary), both of which have resemblances to both Ceratosaurus and Megalosaurus bucklandii. Originally it seemmd as if, as with Ceratosaurus and Megalosaurs, this was a "living fossil" a persistantly primitive form existing alongside more advanced theropods for millions of years. Restudy shows that this species is more likely a basal carchrodontosaur. A second species, K. giganticus, based on a vertebral column, will probably turn out to be a sauropod.

Known from a set of three tall-spined vertebrae is a genus of large theropod dinosaur based on a type specimen of three tall-spined vertebrae found in 1884 in Sussex, England by the fossil collector Samuel H. Beckles. The Megalosaurus in Crystal Palace, London gets its hump from these vertebrae (Dinosaur Mailing List). (Wikipedia) A partial metatarsus and teeth were also attributed.

The nomenclature of this species is rather convoluted. Becklespinax is based on the high-spined vertebrae that were at one time combined with a Megalosaur tooth species to produce Altispinax dunkeri, which was placed in the family Spinosauridae (on the basis of the vertebrae), being assumed to be a more primitive species in which the vertebrae had not yet extended into a "sail". It was then found that the teeth could not confidently be assigned to the same animal as the postcrania, which were reassigned to a new species of Acrocanthosaurus, another high-spined theropod with similar vertebrae. The species was thus called Acrocanthosaurus altispinax. But further study showed it could not confidently be placed with the genus Acrocanthosaurus either. So it was placed in a new genus and is now known as Becklespinax altispinax. for a while is was placed among the Sinraptoridae, as a smaller version of Yangchuanosaurus, a much earlier animal that likewise had a low fin along the back. The discovery of Concavenator shed new light on this species, both lived around the same time and place, Concavenator lived only slightly (i.e. several millions of years) later), and both have the same set of elongate vertebrae. See also brief comments on Thescelosaurus, and more complete comments at the Theropod Database. At the time of writing, the two have not been described in a peer reviewed paper.

Concavenator corcovatus, the "hump backed hunter from Cuenca", is a recently discovered dinosaur from the Las Hoyas lagerstatte, discovered by José Luis Sanz, Francisco Ortega and Fernando Escaso from the Autonomous University of Madrid and the National University of Distance Learning.

Apart from Neovenator, Concavenator is the most primitive known carcharodontosaurid. It is the most complete individual of a carcharodontosaurian theropod, and the first one in which direct and indirect evidence of integumentary structures is reported. This animal is remarkable for the presence of two extremely tall vertebrae in front of the hips formed a tall but narrow and pointed crest on its back. The function of such a crest is not clear; it could be like the head-crests used in intra-species visual displays, or it could also be a thermal regulator (see illustratuion at right), rather the fin or sail on the back of edaphosaur and sphenacodontid pelycosaurs. Similar elongate vertebrae are found in spinosaurs (although they have a longer "sail")

Another curious feature is that the forelimb (ulna) shows evidence of what may be quill knobs or homologous structures, an anatomical feature so far known only in animals with large, quilled feathers on the forelimb. If this is the correct explanation, it shows that feathers appared much earlier in theropod evolution than previously thought (at the avetheropod rather than the maniraptoran grade). Although it is less surprising in view of the presence of tubular quill-like structures in ornithischian dinosaurs such as the heterodontosaurid Tianyulong and the basal ceratopsian Psittacosaurus (Ortega et al 2010, p.205). Darren Naish of tetrapod zoology is sceptical of this interpretation, pointing out that the bumps were unusually far up the arm and irregularly spaced for quill knobs. His alternative explanation is that such structures are found along intermuscular lines, acting as tendon attachment points for example (Naish 2010b).

Eocarcharia (meaning "dawn shark", in reference to its basal status in the "shark-toothed" dinosaurs) is a carcharodontosaurid from the early part of the Middle Cretaceous. its fossil remains were discovered in the Sahara desert (where in places dinosaur bones are just appearing out of the sand dunes) in 2000 on an expedition led by University of Chicago paleontologist Paul Sereno (Wikipedia). It is represented by several cranial bones (fragments of skull & jaws) and isolated teeth. The species name dinops is from the Greek "fierce-eyed", in reference to the massive ornamented brow above the orbit.

This basal carcharodontosaurid is similar to and contemporary with Acrocanthosaurus. (Sereno & Brusatte 2008). The two are sometimes grouped in a single clade, so it is possible they are congeneric, although Paul 2010, who is (like the present author (MAK) a lumper when it comes to species and genera, does not do so here. in any case, the known remains of Eocarcharia are so fragmentary that is difficult to be sure of its exact phylogenetic plaxcement, beyond basal carcharodontosaurid. The presence of a close relative of the North American Acrocanthosaurus on Africa suggests that carcharodontosaurids had already achieved a trans-Tethyan distribution by the mid Cretaceous. (Sereno & Brusatte 2008). This animal was a contemporary of the abelisaurid, Kryptops. The co-exstence of several totally different lineages of large theropods was a common occurance from the Late Jurassic through to the Middle Cretaceous.

A huge preditor, filling the same ecological role in the north as the Carcharodontosaurines did in the south, Acrocanthosaurus is distinguished by tall vertebral spines giving it a metricanthosaur-like appearance. The basal carcharodontosaurid Becklespinax has a similar but taller fin. Acrocanthosaurus, or an animal very much like it, made some of the famous Paluxy River dinosaur tracks in Texas, including a sequence where an individual appears to pursue a large brachiosaurid (probably Pleurocoelus), which also left its great basin-sized prints in the mud. This indicates that this Tyrannosaurid-sized carnivore was not afraid to take on even the biggest sauropods in its environment. Represents a transitional form between allosaurids and primitive charcharodontosaurids and carcharodontosaurines proper. This was the last-known large Allosaurian in North America (Western Laurasia), apart from a relict lineage (Labocania) in the very South-West of the continent. The Acrocanthosaurs disappear at the end of the mid Cretaceous, perhaps victims of the Cenomanian mass-extinction. The Tyrannosaurids take their place in the north. In the south, the Carcharodontosaurines are replaced by Abelisaurs.

Unlike other highly specialised large theropods like Abelisaurs and Tyrannosaurs, Acrocanthosaurus would have used its small but functional forearms to secure prey. The range of motion in the forelimb of Acrocanthosaurus is similar to that of Herrerasaurus and Dilophosaurus, and greater than that of Tyrannosaurus. The limited forward range of motion of the forelimb indicates that Acrocanthosaurus captured prey with its jaws. The forelimb could grasp prey that had been moved by the jaws to beneath the chest. Struggling prey would have been impaled upon the strongly flexed first ungual. Acrocanthosaurus exhibits a greater manual range of motion than ornithomimid and deinonychosaurian coelurosaurs, but less at the shoulder and elbow. Coelurosaurian theropods exhibit reduced digital flexion and hyper-extension, which suggests a change in the use of the hand. Senter & Robins 2005)

In phylogenetic analyses, Acrocanthosaurus is usually placed in the Carcharodontosauridae, less often in the Allosauridae. But see, Currie & Carpenter (2000).

Nine phylogenetic hypotheses, showing various interpretations of Acrocanthosaurus in the Allosauroidea. Analyses along the top two rows recover Acrocanthosaurus atokensis as a member of Carcharodontosauridae, whereas the bottom row represents those that place Acrocanthosaurus atokensis as close relative and/or sister taxon to Allosaurus. Image and some of caption by Eddy & Clarke 2011 fig.33 (doi:10.1371/journal.pone.0017932.g033), Creative Commons Attribution

Known from skull fragments and some vertebrae, and it seems some limb bones, Shaochilong (meaning "shark toothed dragon") is unusual both in its northern distribution and late straigraphic range. Originally identified as a carnosaur of the genus Chilantaisaurus and then a primitive coelurosaur (Wikipedia), a re-description by Brusatte and coworkers in 2009 found that it was in fact a carcharodontosaurid, the first recognized from Asia. Phylogenetic analysis performed by indicate that Shaochilong is deeply nested within the carchorodontosaurids, and appears to be more closely related to the classic Gondwanan carcharodontosaurids (Tyrannotitan, Carcharodontosaurus, Mapusaurus, Giganotosaurus) than the Laurasian ones (such as Neovenator and Acrocanthosaurus). It shows that allosaurs rather than tyrannosaurs were still the dominant group of large-bodied theropods in Laurasian as late as the early Late Cretaceous. Compared to other taxa however it was a small bodied and short-snouted representative of the group. The dominance of the tyrannosaurids in Asiamerica was therefore confined to the very end of the Cretaceous. (Brusatte et al 2009, Brusatte et al 2010b)

Shaochilong maortuensis may or may not be related to Labocania anomala Molnar, 1974 of the Late Campanian El Gallo Formation, Baja California, Mexico, this large but very poorly known animal (estimated length about 7.5 m; weight about 1.2 tons) has been variously interpreted as a tyrannosaur-like allosaurid (Paul 1988) a possible tyrannosauroid (Holtz2004), and an avemetatarsalian, it has also been related to Shaochilong Chure (2000) . Mickey Mortimer suggests carcharodontosaurid related to Shaochilong. As East Asia and Western North America were closely connected during the late Cretaceous, this makes sense from a paleogeographic as well as stratigraphic perspective. If so, two distinct lineages of carcharodontosaurs survived till the end of the Cretaceous, showing that late Cretaceous large theropod diversity was a lot greater than previously realised. This also means that allosaurs were independently evolving tyrannosaur characteristics. Alternatively, and rather more likely given the stratographic and geographic location and morphological characteristics, this could simply be another basal tyrannosaur. In this case, no carcharodontosaurids survived to end of the Mesozoic.