DINSAUROMORPHA |--ORNITHISCHIA `--+--SAUROPODOMORPHA `--Theropoda |--Herrerasauridae |--Ceratosauria `--Tetanurae |--Torvosauroidea `--Avetheropoda |--Carnosauria `--Coelurosauria |--Tyrannosauroidea `--Maniraptora |--Dromaeosauridae `--AVES
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. We may consider the Megalosaurs as being made up of a number of families, as detailed below.
Megalosauridae. This group includes Megalosaurus, Torvosaurus, Poikilopleuron, and possibly also Edmarka, Erectopus, and 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.
Spinosauridae. Among the more unusual of the theropod dinosaurs, spinosaurids 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 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 mamamlian 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. affirm 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.
Of the spinosaurids, 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. 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.
Eustreptospondylidae. 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 megalosaurs 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 (i.e.: This is Carnosauria plus Coelurosauria; Coelurosauria includes Tyrannosaurus, Velociraptor, Oviraptor, and birds). MAK010506
Theropoda: Eoraptor. Neornithes > Cetiosaurus. Padian et al. (1999).
Range: From Late Triassic.
Phylogeny: Saurischia: Sauropodomorpha + *: Herrerasauridae+ (Ceratosauria + Tetanurae).
Characters: $ skull pneumatized; nares formed by premaxilla & nasals, excluding maxilla [CC00]; nasal cavities communicate laterally to large diverticula at antorbital fossa; promaxillary fenestra usually present at anteroventral apex of the antorbital fossa [CC00]; $ lacrimal extends to top of skull; horns & crests (display?) common; nasals usually unsutured at midline [CC00]; other diverticula invade palate & peri-orbital bones (antorbital diverticula increase in advanced species.); trend to more anterior-facing orbits and increased brain size; opisthotic and exoccipitals always fused; $ intramandibular joint present; external mandibular fenestra present [CC00]; posterior end of angular usually anterior to articular; long palatine-maxilla suture; some have diverticula from throat through middle ear to braincase; $ angular with anterior hook; teeth usually laterally compressed, curved, with 2 serrated edges; normally 23 pre-sacral vertebrae; $ prominent prong-shaped cervical vertebral epipophyses (lost in some advanced species.); long caudal prezygapophyses; limb bones extensively pneumatized, as are ribs & vertebrae; diverticula may communicate with lungs; $ strap-like scapula; humerus <50% of femur; $ metacarpals I-III dorsally pitted (ligament attachments); phalanges of hand elongate; loss or reduction of manus 4 & 5; $ claws, especially on manus, long curved & sharp; ilia large and blade-like; expanded distal end of pubes ("pubic boot"); astragalus tends to enlarge, calcaneum to be reduced lost; astragalus with pronounced ascending process; metatarsals tend to increase in size relative to femur; pes 1 tends to develop large "raptor" claw; metatarsals II & IV come in contact & metatarsal III reduced (shock-absorbing arctometatarsalia); note several adaptations for increased speed. Diversity markedly higher than herbivorous dinosaurs in any given location, but species less localized.
Image: Eoraptor: upper sketch by Rob Gray, reproduced by permission. Lower photo from the Wittmer Lab.
Links: DinoData: Theropoda; Theropod Dinosaurs; Theropoda -- The Dinosauricon; Lectures 19-20: Late Cretaceous; Lecture 19 - Late Jurassic: Solnhofen; GEO212 HOMEPAGE. Dinosaur Paleontology (cranial anatomy); UTCT Image folio: Birds and their Dinosaur Relatives; Theropoda (German); Theropoda (Tree of Life); Theropod - Paleontology and Geology Glossary; FPDM - Theropoda (Index to the excellent Fukui Prefectural Museum pages); Theropoda; Discovery and Classification | Theropoda; THEROPODA (German); ??:????? Theropoda (Japanese); Witmer's Lab Dinosaur Skull Collection- Theropoda (of many good sites, Best on the Web); Theropoda List (another Japanese model site); Literature - Theropoda; GEOL 104 Lecture 22- Theropoda I- Dinosaurs red in tooth and claw; National Dinosaur Museum - Theropoda; GEOL 104 Lecture 24- Theropoda III- Raptors, Archaeopteryx, and ...; Nathis Fauna Dinosauria Sauirschia Theropoda (Dutch); Theropoda - families after Paul, 1988; Theropoda (selected synapomorphies).
References: Currie & Zhao (1993); Currie & Carpenter (2000) [CC00]. ATW060214.
Herrerasauridae: Herrerasaurus, Staurikosaurus.
Introduction: These medium-sized hunters are the earliest known and most primitive dinosaurian lineage. They died out before the Triassic period ended. There is some disagreement whether Herrerasaurs should be considered primitive theropod saurischians or pre-saurischian dinosaur ancestors. If herrerasaurs are theropods, that indicates that the three main dinosaurian groups diverged very early on, and that all three lineages independently eveolved several dinosaurian features, such as a more advanced ankle joint or, say, an open acetabulum (where the hind limb attaches to the pelvis). Indeed, the discovery of the extremely primitive prosauropod Saturnalia seems to confirm this. (adapted from MAK)
Range: Late Triassic of South America & North America.
Phylogeny: Theropoda: (Ceratosauria + Tetanurae) + *.
Characters: 2-5m bipedal predators; large teeth; intramandibular joint; vertebrae: 15+9+2+~50 (note primitive 2 sacrals); dorsal vertebrae and processes axially compressed; accessory dorsal intervertebral articulations present; axial skeleton pneumatized; distal caudal prezygapophyses overlap next vertebra; scapula narrow & unexpanded; well developed acromial process of scapula (deltoid muscle); elongated manus; manus IV&V greatly reduced, I, II, and II elongate w large claws; but acetabulum bony and only slightly perforate; brevis fossa insignificant; great distal enlargement of pubis; leg primitive; pes with 5 digits; pes I-IV with uncurved claws.
Links: DinoData Herrerasauridae; Herrerasaurus; Introduction to Herrerasaurus; Herrerasaurus & Eoraptor: The Oldest Dinosaurs; DINOBASE, Sibbick's dinosaur pictures; Re- Herrerasauridae; Herrerasauridae; MEA592D Dinosaur Osteology- Lecture 4; van Dijk's Dinosaurus Sted - Herrerasaurus. Referencer; SVPCA 2000 -Abstracts LM; Darren Naish. ATW031204.
Ceratosauria:(=Coelophysoidea?): Coelophysis, Dilophosaurus, Abelisaurs. Definition: Ceratosaurus > birds. Padian et al. (1999)
Introduction: The Ceratosaurs are the earliest and most primitive theropods proper. They often feature unusual crests on their head, perhaps a device for intraspecific rivalry or mating. They seem to have become extinct during the end Jurassic in Laurasia, although if abelisaurs are Ceratosaurs (and this is generally stated but still not certain), than these animals survived in Gondwanaland right up to the end of the age of dinosaurs.
A 1994 analysis by Holtz has coelophysoids and neoceratosaurs forming a clade (Ceratosauria), and together forming the outgroup to Tetanurae. That is the scheme adopted here. It has been suggested that these two taxa may not form a clade exclusive of other known theropods. There are also some derived features found in neoceratosaurs (Ceratosaurus and Abelisaurs) which are not found in coelophysoids. This could be evidence that neoceratosaurs are closer to tetanurines than to coelophysoids. In this case, the neoceratosaur/coelophysoid characters would have to be convergences and/or primitive neotheropod features lost in Tetanurae, and the Ceratosauria are paraphyletic or even polyphyletic. (adapted from MAK)
Range: Late Triassic to Late Cretaceous.
Phylogeny: Theropoda: Tetanurae + *.
Characters: Maxilla & premaxilla weakly attached; large tooth from lower jaw fits into marked diastema; no maxillary fenestrae; $ 2 pairs of pleurocoels in cervical vertebrae; $ fusion of sacral vertebrae & ribs (adults); retain 4 digits in hand; $ 2 fenestrae in pubic plate; $ flange at distal end of fibula overlaps ascending process of astragalus anteriorly. Monophyly not certain; group poorly known except Coelophysis. Ceratosaurus may not be in the Ceratosauria.
Image: Liliensternus liliensterni, artwork © M. Shiraishi, reproduced with permission
Links: DinoData: Ceratosauria; DinoData: Coelophysis; Ceratosauria; Coelophysis; Staab Studios - Coelophysis Model; Coelophysoidea -- The Dinosauricon; The Fernleaf: Karen Carr; Ceratosaurian Theropods; Ceratosauria (Mikko's Phylogeny); Ceratosauria (Dutch -- brief introduction & chart); A BASAL ABELISAURIA NOVAS, 1992 (THEROPODA- CERATOSAURIA) FROM ... (full text paper on relationships); Megalosaurus = Torvosaurus in Europe (and following); ceratosauria.htm (Justin Tweet); Dinosaurier Interesse.de - Stanley- Ceratosaurier (German); GEOL 104 Lecture 22- Theropoda I- Dinosaurs red in tooth and claw (lecture notes from Tom Holtz); Ceratosauria. ATW030313.
Tetanurae: Definition: birds > Ceratosaurus. Padian et al. (1999)
Introduction: The Tetanurae ("stiff tails") consist of a number of parallel lines, all of which seemed to have evolved increasingly bird-like features. For example, their rib-cages indicate they had a sophisticated air-sac-ventilated lung system, which exists today only in birds. Such an advanced respiratory system would have been accompanied by an advanced circulatory system (even the ectothermic crocodiles (the nearest living dinosaur-ancestors after birds) have an efficient four-chambered heart, like mammals and birds, rather than the inefficient three-chambered reptile heart). All this indicates a high metabolic rate; like birds, advanced theropods were certainly endothermic (warm-blooded).
The clade Tetanurae includes both birds and the most famous of classic theropods. All Tetanurans lack the fourth digit of the hand, have all their maxilliary (upper jaw) teeth in front of their eyes, have a strap-like scapula (shoulder blade), and various other anatomical characteristics, which indicate that all tetanurans evolved from a single common ancestor. Tetanurans are generally subdivided into two clades, the Carnosauria and the Coelurosauria. (adopted from MAK)
Range: From Early Jurassic.
Phylogeny: Theropoda:: Ceratosauria + *: Torvosauroidea + Avetheropoda.
Characters: $ Increased pneumaticity of skull; nasals narrow & elongate [H+01]; $ maxillary fenestrae present; $ maxillary teeth only anterior to orbit(?) or to antorbital fenestrae(?); procoelous dorsal vertebrae [H+01]; stiffened tails (reduced importance of tail in walking?); scapula straplike [H+01]; coracoid tapers posteriorly [H+01]; $(?) metacarpals 1&2 broadly in contact [H+01]; $(?) manus with 3 digits; manus elongate [H+01]; $(?) obturator notch on ilium; $ fibula reduced and "clasped" by tibia; $ anterior horizontal groove on astragalar condyles.
Note: Sereno's (1999) diagnosis of the Tetanurae seems to include features more appropriate to Avetheropoda and Maniraptora.
Links: DINODATA; Tetanurae: From Meek to Fierce; Tetanurae--croc-mimics to flying beauties; Tetanurae -- The Dinosauricon; Selected Synapomorphies.
References: Hutt et al. (2001) [H+01].
Torvosauroidea: Spinosaurs, Torvosaurids (=Megalosaurs), Afrovenator, Suchomimus.
Range: Late Jurassic-Late Cretaceous.
Phylogeny: Tetanurae: Avetheropoda + *.
Characters: In essence, all Tetanurae other than Avetheropods. May be para- or polyphyletic. Known material is scrappy and includes both highly derived Spinosaurs as well as relatively general Allosaur-like Torvosaurids. Elongated rostral ramus of maxilla; pinched rostral ramus of lacrimal; $ large sickle claw on manus 1.
Links: Tetanurae -- The Dinosauricon; Torvosauroidea; Re- Torvosauroidea was [R- Torvosaurus & Giganotosaurus];