The Megalosaurs evolved from a Coelophysid- or Ceratosaurid- like ancestor during the later Triassic, and seem to have been the dominant large preditor by the middle Jurassic before being supplanted by the Allosaurs. Cretaceous forms were specialised semi-aquatic fish-eaters and mostly confined to Gondwanaland. They seem to have died out some time during the earlier late Cretaceous. The terms Megalosaur, Megalosauridae, etc are rarely used nowdays, as firstly the original or type species of Megalosaurus is known from only very fragmentary material, and secondly Megalosaurs are a paraphyletic group, defined mostly by shared primitive features, and hence not considered valid in the current, cladistic, paradigm. Megalosaurs represent a sort of intermediate group that does not fit in neatly with either the Ceratosauria or the Tetanurae, although nowadays the tendency is to consider at least some megalosaurs (or Torvosauroidea or Spinosauroidea, to give the preferred cladistic terms, based on better known material) as the most primitive (basal or underived) members of the Tetanurae ("stiff tails"), a clade that includes both birds and the advanced theropods. Megalosaurs were previously included with the Allosaurs and Tyrannosaurs in the polyphyletic (artificial) taxon "Carnosauria." The old-style definition of Carnosaurs is actually an ecotype rather than a true evolutionary group, designating any large (around 200 kg or more in weight) carnivorous theropods, posessing large skulls, short necks, and small forearms.
The following families of Megalosaurs could be suggested (following here the Linnean/Evolutionary Systematic methodology):
The relationship of the Cretaceous Gondwana theropods known as Abelisaurs is still unclear. They may be either primitive Megalosaurs or advanced Ceratosaurs.
A more detailed representation (in terms of a cladogram) is as follows:
<==o Megalosauria |-?? Kelmayisaurus |--o Megalosauridae [= Torvosauridae] | |?- Magnosaurus | |?- Megalosaurus | |-- Poekilopleuron | `-- Torvosaurus |-??Abelisauridae |--o Spinosauridae | |--o Baryonychinae | | |-- Baryonyx | | `-- Suchomimus | `--o Spinosaurinae | |-- Irritator | `--o Spinosaurus `--o-Eustreptospondylidae `--+-+Afrovenator | `--Eustreptospondylus |--Allosauria `--Coelurosauria
This group includes Megalosaurus, Torvosaurus,Poikilopleuron, and possibly also Edmarka, Erectopus, Xuanhanosaurus These were large animals (9 to possibly as much as 15 meters), with short, stout arms. The old name Megalosaurus has been pretty much universally discarded in favour of Torvosaurus. This is a shame I feel, because Megalosaurus has a nice historical heritage. The English species Megalosaurus bucklandii was the very first dinosaur to be described, some years before Richard Owen coined the term Dinosauria in 1842. Unfortunately, the name Megalosaurus, like Plesiosaurus, became something of a taxonomic waste basket, and there is some doubt now among paleontologists whether it even is a valid genus. That is, although the remains are of a large primitive theropod dinosaur of "megalosaur" (or torvosaur) relationships, it is not possible to identify them more closely. At present there are three species still included. If the name Megalosaurus is shown to be invalid then the terms Torvosauridae, Torvosauroidea and Torvosauria will probably used as higher taxonomic rankings instead of Megalosauridae etc.
?Megalosaurus cambrensis (Newton, 1899)Zanclodon cambrensis Newton, 1899 Horizon: Rhaetic beds of Mid-Glamorganshire, Wales
Comments:If this is a megalosaur it the oldest member of the family. It is based on a dentary nearly identical to that of M. bucklandii. Because it is much older than any other megalosaurs, further material is required to establish its relationships.
Magnosaurus nethercombensis Huene, 1932Megalosaurus nethercombensis, Huene 1926a
Comments:This fragmentary, probably juvenile theropod may or may belong in the genus Megalosaurus. The dentary (lower jaw bone) is very similiar, but the distal tibia is (unlike M. bucklandii) not compressed.
Megalosaurus hesperis Waldman, 1974Horizon: Upper Inferior Oolite of Dorset, England
Comments:From the little that is known of it this early, medium-sized animal seems to be quite similar to M. bucklandii.
Megalosaurus bucklandii Meyer, 1832type species
Comments:The first dinosaur to be named, this specimen is known from fragmentary remains. The original specimen was a dentary, but many other elements have been referred to it. The genus Megalosaurus is something of waste basket or taxon for poorly known mostly Jurassic theropods. This was a rather big animal, clearly the top preditor of its day.
Poekilopleuron bucklandii Eudes-Deslongchamps, 1838Horizon: Calcaire de Caen, Calvados, France
Comments: The fate of the original specimen was rather unfortunate. Apparently fairly complete when found, a lot of the material was destroyed before collection, and the rest during WWII. Subsequent discoveries of theropod remains from France may belong to this species.
Torvosaurus tanneri Galton and Jensen 1979asynonyms: Edmarka rex Bakker, Kralis, Siegwarth, and Filla, 1992
Comments: Among the largest of the Morrison preditors, this animal was larger and more heavily built than Allosaurus. Yet it has a number of primitive features that indicate relationships with typical Middle Jurassic theropods like Gasosaurus and Poekilopleuron. The absense of a calcaneal notch, already present in the much earlier Eustreptospondylus, indicates that, like Ceratosaurus, this animal was a sort of "living fossil", continuing to survive and flourish alongside much more specialised and advanced theropods
Among the more unusual of the theropod dinosaurs, spinosaurians were lightly built predators with elongated vertebral spines and crocodile-like jaws with specialized teeth. Fish probably formed most of their diet. Two main groups exist: the baryonychids, who are most famous for their elongated, many-toothed skulls and large hand claws; and the spinosaurids, which had more cranial ornamentation and generally a larger sail (reminiscent of the pelycosaur Dimetrodon).
Spinosaurids, like the recently discovered Suchomimus, have very short and stocky arms, thumb claws which are dramatically larger than the other unguals, unguals with greater angles of curvature, a tapering shaft, and more oval slender cross-section (like that of a carnosaur or Torvosaurus claw).
Spinosaurid teeth are much more oval in cross-section than in typical theropods.
There are a number of crocodilian like features in the skulls of spinosaurids: including the elongate snout, conical teeth, secondary palate (so it could breath through it's nostrils, even while the mouth is closed, a mmamlian feature not shared by most reptiles), and more. These features have been associated with the adoption of a piscivorous diet in crocodylomorph evolution. As with modern crocodiles, spinosaurs were not obliged to only eat fish. They could eat land animals as well. Remnants of Iguanodon bones as well as Lepidotes fish scales are found among the fossil stomach contents of Baryonyx The paleoenvironments from which known spinosaurids come all support diverse communities of fish, some of which were very large. There is currently no evidence that these were seasonal communities, and would seem likely to be permanent residents. Thus, we have very large packages of fish meat not otherwise easily exploitable by theropods, although they would have been in competition with contemporary giant crocodiles.
The relationship of the Spinosaurids is not completely clear, although the most likely option is that the Spinosaurs are cousins to the Megalosaurids. Greg Paul in his Predatory Dinosaurs of the World however suggests that they might actually be late surviving (and giant) Coelophysoids. An interesting piece of evidence here is the presence of a "subnarial gap" or kink in the jaw, under the nostrils, that is found only in the Coelophysoidea and Spinosauridae. There is no evidence of a ' subnarial gap ' in any other theropods groups outside of those two. It is however a feature that is common in archosaurs in general. Eoraptor apparently has a subnarial gap, but Herrerasaurus does not. There are differing views over whether either is a true theropod
However in an scientific paper Paul Sereno et al affirms Megalosaur (Torvosaur) relationships. There may be only a superficial resemblence between Spinosaurids and Coelophysids in respects to the premaxillary/maxillary portion of the skull in profile. In addition, the anatomical arrangement in coelophysoids differs from the condition in spinosaurids (although the latter could be derived from the former). But now that the postcranial anatomy of spinosaurids are a lot better known than back in the mid-1980s, it seems that there is not much in the rest of the skeleton to link spinosaurids and coelophysoids.
Some restorations of spinosaurians made recently show them as quadrupedal, a mistake based on early descriptions of the arms of Baryonyx.
Baryonychines are characterized by (among other traits) the increased number and decreased size of dentary (jawbone) teeth (about 30) and a blade-shaped ventral keel to the anterior dorsal centra of the vertebrae.
Baryonyx walkeri Charig and Milner, 1986Horizon: Wealden formation of Surrey, England and Spain
Comments: Known from most of a skull and sleton, this is the most complete theropod dinosaur unearthed to date in Britian. Originally referred to as the "Surrey dinosaur", and nicknamed "Claws" on account of its huge claws, which conjured images of a gigantic dromaeosaurid, this animal is now known to be a close relative of Spinosaurus. It was probably a fish-eater. Suchomimus is a close relative, and probably belongs in the same genus.
Suchomimus tenerensis Sereno, Beck, Dutheil, Gado, Larsson, Lyon, Marcot, Rauhut, Sadleir, Sider, Varricchio, G. Wilson, and J. Wilson, 1998Horizon: Elrhaz Formation, Tenere Desert region, Niger.
Comments:Suchomimus had an elongate snout and piscivorous adaptations that make the skull resemble a fish-eating crocodilian such as the gavial It differs from Baryonyx in that the snout is even more crocodilian like. The skull is estimated at about 1.2 m (4 ft) in length, the overall creature was 11 meters or more. The robust forelimbs armed with very large curving claws, including a sickle-like thumb, that could be used like gaffing hooks on fish or other prey. Tall blade-like neural spines ran along its back, rising into a low (60cm tall) "sail" over the hip region (sacral vertebrae) and base of the tail.
Nearly 3.5 m (12 ft) high at the hips, Suchomimus may have waded into rivers and lakes like to catch fish, but probably could swim in deeper water as well, using its back legs and possibly its tail for propulsion. Suchomimus may have swept its mouth back and forth through the water, much like a pelican, and snapped when it encountered prey. This would allow it to keeps its eyes above the waterline and still reach down into the muddy waters for large lungfish.
Fish-eating habits are indicated by structural parallels with modern crocodiles. Crocodiles species such as the Nile, Salt-Water, Muggers have jaws on par with Baryonyx walker. Although thinner than most animals but still wide enough and strong enough to take down large animals like water buffalo. The piscivorous crocodylians like the gharial and false gharial and the African slender snouted croc all have jaws suitable for fishing and small animal catching. If they were to attempt to tackle a large animal their jaws would snap under the stress. Suchomimus tenerensis had jaws like the latter, so the same rules seem to apply.
Unlike conventional fish-eaters Suchomimus had relatively high skull. Piscivores need a long low skull so they can swip the skull through the water to catch fish. Onviously Suchomimus 's methods of catching food were different to crocodiles.
Suchomimus is likely to have eaten land animals as well as fish. It had a relatively long, thin neck, plus very strong forearms and massive (by theropod standards) shoulders. It shared the local environment with a massive (10-15 meter) crocodile, built on a rather modern design, which occupied the lurk-in-the-water carnivore niche. The long jaw was better able to withstand twisting than the wider skull of Carcharodontosaurus, so it would have attacked different, probably smaller, prey on land. The thin jaws could not have tackled animals like iguanodonts.
There is little to distinguish Suchomimus from Baryonyx and Cristatusaurus, and it is likely that all three belong to the same genus (Baryonyx).
Spinosaurines are characterized by very straight teeth lacking serrations, and lack the derived increase in dentary tooth number. The difference between baryonychine and spinosaurine teeth is that spinosaurine teeth seem to be less curved, whereas baryonychines retain something closer to the original theropod curvature in lateral view. They remain, however, much rounder in cross-section than allosaur or ceratosaur teeth of the same height.
Spinosaurus aegyptiacus Stromer, 1915Horizon: Baharija Beds of Egypt, also Morocco
Comments: A huge but lightly built animal, with vertebral spines taller than a man (the tallest part of the large bony sail is over the thorax - the mid-dorsal vertebrae), Spinosaurus did not seem to compete with the contemporary Cacharodontosaurs. Perhaps, like the Baryonchines, it was semi-aquatic; probably a fish-eater. Early illustrations wrongly showed Spinosaurus to resemble a conventional carnosaur (like Allosaurus) with a Dimetrodon-style sail or fin on the back (there are still some illustrations that show Spinosaurus as a chunky animal with long thick forearms, sometimes in a quadrapedal pose). The remains were lost in WWII. Spinosaurus marrocanus Russell, 1996, from the ? Albian of Morocco may or may not be the same species. Material dubbed "Spinosaurus B" appears to belong to two theropods: the vertebrae to Sigilmassasaurus, and the limb material to the allosaur Carcharodontosaurus.
At present Irritator is the only known member of this clade.
Irritator challengeri Martill, Cruickshank, Frey, Small, and Clarke, 1996synonym: possibly Angaturama limai Kellner and Campos, 1996
Comments: This animal's name comes from the fact that the skull was both damaged and artificially lengthened by amateur fossil hunters before it was described. Angaturama limai Kellner & Campos, 1996, another unusual theropod from the same formation, consisting of the front part of the jaws, is probably from the same species.
The family Eustreptospondylidae was coined by Gregory Paul to include a number of advanced megalosaur and primitive allosaur like animals. All have the allosaur-like flexible ball-annd-socket neck articulation, but in other respects they are too primitive to be considered allosaurs. The family is now limeted to Eustreptospondylus only, but he early Cretaceous Afrovenator may also belong here. The status of other forms like Piatnitzkysaurus, Gasosaurus, and Marshosaurus is unclear. Paul considered them Eustreptospondylids, but they would seem to be now included among the Allosauroidea (family Sinraptoridae). In any case, this shows that there is no sharp dividing line between Negalosaurs and Allosaurs, but rather an evolutionary gradation. In any case, the Eustreptospondylids were very large animals (around 8 meters), close to the ancestry of the Avetheropoda clade (i.e.: This is Carnosauria plus Coelurosauria; Coelurosauria includes Tyrannosaurus, Velociraptor, Oviraptor, and, cladistically but not linneanly speaking, birds).
Eustreptospondylus oxoniensis Walker, 1964synonyms: Megalosaurus cuvieri, Streptospondylus cuvieri
Comments: Among the better known of the middle Jurassic theropods (and until the discovery of Baronyx the most complete theropod skeleton from England), this animal is more or less intermediate between Megalosaurus and more advanced forms like Allosaurus.
Afrovenator abakensis Sereno, Wilson, Larsson, Dutheil, and Sues, 1994Horizon: Niger
Comments: Another one of the intermediate theropods, halfway between megalosaurids and spinosaurians on the one hand, and Allosaurus and avetheropods on the other, this respectable-sized animal seems similiar to Eustreptospondylus and can tentatively be included in the same family. It is interesting in that it continued to survive millions of years after its Allosaur and Coelosaur "nephews" appeared. This is one of the better known types of dinosaur, and in fact the most complete skeleton of a Cretaceous carnivore ever found in Africa (most dinosaurs are only known from a few scraps of bone).
Kelmayisaurus petrolicus Dong, 1973Horizon: Lianmugin Formation, of Sichuan, China
Comments: This theropod is based on parts of the upper and lower jaws, both of which have resemblances to both Ceratosaurus and Megalosaurus bucklandii. As with Ceratosaurus and Torvosaurus, here we have a "living fossil" a persistantly primitive form existing alongside more advanced theropods for millions of years. Possibly this represents a distinct, perhaps isolated, family, which could be appropriately termed the "Kelmayisauridae". A second species, K. giganticus, based on a vertebral column, will probably turn out to be a sauropod.
Walking With Dinosaurs
Theropods of Dry Mesa Quarry - Torvosaurus - includes Torvosaurus - discussion (evolutionary relationships between Torvosaurus and other Megalosauria) - Best of the Web
Torvosauroidea - Palaeos
A Cruel Sea - Eustreptospondylus puts in an appearance. See the dvd of the series:
Tetanurae - Thescelosaurus!
Spinosauria by T. Mike Keesey - definition of the group and list of every known species
Jurassic Gallery - fantastic artwork by M. Shiraishi. By Japanese and English
Spinosauroidea Mikko's phylogeny site
Gregory S. Paul, Predatory Dinosaurs of the World Simon and Schuster, New York, 1988 - okay it's out of print and dated in parts; and needs to be revised in the light of more recent discoveries - I still give it Best Book rating
Molnar, R. E., Kurzanov, S. M., & Dong, Z., 1990: Carnosauria. in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.), 1990: The Dinosauria, University of California Press, Berkley, Los Angeles, Oxford, pp.169-209
A Long-Snouted Predatory Dinosaur from Africa and the Evolution of Spinosaurids Paul C. Sereno, et al
One Tough Dinosaur Discovered
Dinosaurs of the Sahara - includes web cam - at National Geographic
Charig, A J and Milner A C. 1997. Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bulletin of the Natural History Museum of London (Geology) 53:11-70.
Taquet, Ph and Russell, D A. 1998. New data on spinosaurid dinosaurs from the Early Cretaceous of the Sahara. C. R. Acad. Sci. Paris, Sciences de la terre et des planetes 327:347-353.
cautionary note (please read before using this page as reference material!)