Theropoda: Avetheropoda

With the exclusion of Tyrannosauroidea (now considered a giant Coelurosaur lineage), only the Allosaurids and their relatives make up the Carnosauria. The name "Allosauria" was coined by Greg Paul in his superb book Predatory Dinosaurs of the World and seems to have caught on, although "Carnosauria" is still sometimes used. In any case, these were big to enormous bipedal terrestrial preditors, that for some one hundred million years or so were the dominant form of life on land.

The stem-based definition of Carnosauria is more inclusive than the node-based definition of Allosauroidea (definitions from Carnosauria (in Polish)):

• Carnosauria (Huene, 1920): the largest clade that includes Allosaurus fragilis but not Passer domesticus (modified from Padian and Hutchinson, 1997)
• Allosauroidea (Marsh, 1878 vide Currie and Zhao, 1994) the smallest clade that includes both Allosaurus fragilis & Sinraptor dongi (Holtz, Molnar and Currie, 2004; modified from Padian and Hutchinson, 1997)

With new phylogenies reshufling basal tetanuran and avetheropodan taxa, some of which were only recently described to begin with, it has become hard to know if a primitive theropod is a basal Allosauroid, a non-Allosauroid (i.e. stem-taxon) Carnosaur, a basal Megalosauroid, or a basal Tetanuran! Monolophosaurus for example has been considered all of these at some point or another. With the main debates in early theropod evolution being now about whether a taxon belongs in a monophyletic Megalosauroidea or paraphyletic basal Tetanura, or either of the latter or Avetheropoda, or vs Avetheropoda, most cladograms now have a simple node that is not distinguished further for re Allosauroidea/Carnosauria.

Known from a partial skeleton and compressed skull, Monolophosaurus is a medium-sized early theropod distinguished by a single very large midline ridge-like head crest running from its nose to the rear of the skull. Beyond that, there is nothing particularily distinctive about it, and, as with its megalosaur cousins, exactly where it belongs on the theropod evolutionary tree is a matter of some controversy. The situation here seems to be very similar to that of Piatnitzkysaurus, another mid Jurassic theropod that has had the misfortunate of being bounced all aroudn the theropod family tree by rival phylogenetic analyses.

Originally, things were pretty straightforward. Holtz 2000,Holtz et al 2004, Novas et al 2005, and Corria & Currie 2006 are among the references that considered it an early allosauroid, which places it here among the avetheropods. Pretty soon however things started to go stemward. Smith et al. (2007), in a radical study using Cryolophosaurus (until then considered an allosaur) reinterpreted the positions of many taxa, and demolished the old clades Ceratosauria and Coelophysoidea, and found Monolophosaurus to be as a basal avetheropod. Similarily, Rauhut 2003 had previously found this species to be part of a paraphyletic megalosauria leading to allosaurs. Worse was to come with Benson, 2008b, in a paper on European megalosaurs, noting various primitive features of the skull and skeleton suggest that Monolophosaurus is actually a basal megalosauroid. This position was also recovered in a cladogram by Cau, et al 2011 in a paper on carcharodontosaurs. The implication here would be that characters previously considered apomorphies of the Allosauroidea are plesiomorphic (shared primitive traits, not unique to allosaurs) (Zhao et al. 2010 and Brusatte et al. 2010). Mickey Mortimor mega-matrix analysis finds it to be either a sister to Avetheropoda or a basal megalosauroid. As against placement as a basal tetanuran, a cladogram in the recent a paper on on the megalosaur Eustreptospondylus (Sadlier et al 2008) and another of the advanced allosaur Acrocanthosaurus atokensis (Eddy & Clarke (2011)) both recover Monolophosaurus as a basal allosauroid. This brings us full circle, and we are back where we started after oceans of ink and reams of computer print-outs. It is pretty clear here as elsewhere that the choice of taxa and traits keyed into to the analysis would determine the outcome of the cladogram. It may be that a monophyletic Allosauroidea has to be replaced by any number of parallel megalosaurian lineages. Or this may simply be an example of mosaic evolution, a common feature in transitional taxa, so that early allosaurs or avetheropods were megalosaur-like, primitive basal megalosaur-like, in many ways. Or that Mid Jurassic theropod evolution is such a jumble that a lot more material is required before any even half complete phylogeny can emerge. For now, we've gone with the mosaic evolution option and retained Monolophosaurus as a basla carnosaur, although Smith et al. (2007)'s similar interpertation of this species as a basal avetheropod may be equally valid

Incidentally, Monolophosaurus wasn't the only theropod with a mono loph. A similar but even more exaggerated feature is found in the contemporary basal tyrannosaur Guanlong wucaii. If Monolophosaurus is a basal tetanuran then the two are not related and such characters would arise through convergence ( Brusatte et al. 2010). If Monolophosaurus is a primitive avetheropod (whether stem-avetheropod or stem-carnosaur) then the two would only have fairly recently diverged, and these sort of crests may well be a common shared characteristic among basal avetheropods. The appareance of paired crests among ancestral neotheropods (podokesaurs) and horns and ridges among ceratosaurs and abelisaurs illustrates the repeated occurance of exotic head structures among theropods, doubtless for intra-specific display.

Monolophosaurus has been related to another taxon, Chuandongocoelurus (Benson, 2008b), known only from a single medium-sized partial skeleton, although the association isn't very strong (see Theropod database for comments), and was later considered a more basal form (Ortega et al 2010). If they are related they would constitute an endemic theropod clade (to which we could give the informal name Monolophosauridae (Bakker 1997), so far known from the Middle Jurassic of Asia (Zhao et al. 2010). But this may however be yet another example of convergence. Also, because no skull is known for Chuandongocoelurus, comparisons with Monolophosaurus and other taxa are made more problematic.

Allosauroidea proper is now considered a monophyletic clade divided into three similiarily monophyletic families: the Sinraptoridae, the Allosauridae, and the Carcharodontosauridae.

Greg Paul considers the small late Jurassic Ornitholestes and the earlier and larger Proceratosaurus to be also Allosaurs. This has not caught on, and current understanding classifies Ornitholestes as a basal (i.e. primitive/ancestral) coelurosaur, while Proceratosaurus has recently been identified as a basal tyrannosaur.

Known from a fragmentary skeleton, this medium-sized theropod may be a sinraptorid (Mateus (1998), Benson, 2008, 2010) an unspecified carnosaur (Holtz et al 2004), an allosaur (Paul 2010), , or a distinct non-avetheropod tetaneran clade that also includes Streptospondylus (Mickey Mortimer). In any case, it represents a more primitive form than Allosaurus and Acrocanthosaurus (Mateus (1998)). If it is a sinraptorid it shows the lineage was established in Europe as wlel as China. Of course, Sinraptorid attributes may simply be common primtive characteristics, as well as some specialised traits that were lost in more advanced forms. This means that whilst Lourinhanosaurus may be a sinraptorid grade theropod, it still may or may not be necessarily a sinraptorid in the strict sense

These are the most primitive allosauroids, although even at this early stage they were equipped with elaborate crests. While several European theropods have been placed here, it is not sure if they belong here, as many known only from quite inadequate material. Sinraptorids proper are known from China (hence sinraptorids), but that is more likely because Chinese dinosaur fossils are the best representatives of the middle Jurassic, rather than the group itself being limited to that region. However, it is still possible that Eastern China was cut off from the rest of Laurasia, as a distinctive fauna (Shunosaurine sauropods, Beinotheroides tritylodontids, and brachyopoid labyrinthodonts, seem to be indiginous to that region.

Known from complete skulls and the majority of a skeleton, this was a typical large theropod. It's cranial ornamentation is rather modest. S. hepingensis is a closely reated species, or perhaps a synonym (see Thescelosaurus! website). If Yangchuanosaurus and Sinraptor are co-generic, than the former name has priority, and this species becomes Yangchuanosaurus dongi (Paul 2010)

The holotype of Sinraptor dongi is not fully mature. The remains bear unhealed bite marks (possibly related to the animal's death), as well as healed broken ribs.

The largest carnivore of its time, this three and a half tonne preditor dominated its enviroment. The cranial ornamentation involves dual ridges above the snout and eyes. It also has a low fin fin, down its back, again, possibly for display purposes. Greg Paul (1988) considered this species similiar enough to go under Metriacanthosaurus. It is very similar to S. dongi

From the little that is known of this animal (a few postcranial elements: some vertebrae, a femur) it appears similar to the Sinraptorids, where it is usually placed (Paul 1988, Benson, 2010). The two also lived at more or less the same time. The presence of fin-like ridge along back (as indicated by the tall-spined vertebrae) meant that for a long time this animal was considered an ancestral spinosaurid (Steele, 1970). As Justin Tweet (Thescelosaurus! website) notes, following a brief fifteen minutes of fame in the 1980s (thanks to Greg Paul's Predatory Dinos of the World, associating it with Yangchuanosaurus, or rather vice-versa) and 1990s (because of Paul's influence the name showed up in the movie version of Jurassic Park), this taxon sank back into obscurity.

Because the more recent name Sinraptoridae (Currie & Zhao 1994), is used instead of the first published name, Metriacanthosauridae (Paul 1988), it has been suggested the latter should take precedence. But because it was not accompanied by a formal description, it cannot be considered a scientific valid under formal rules of nomenclature. In any case it is no longer used, not even by Greg Paul himself, we have not tried to revive it. Perhaps this is understandable given the scrappy nature of the eponymous genus. We've placed Metriacanthosaurus next to the sinraptorids, but it may well turn out to be a totally different lineage of early avetheropod. If neither Metriacanthosaurus or Lourinhanosaurus are sinraptorids, then the latter taxon is endemic to China, home of many unique Jurassic dinosaurs