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Dinosauria  main page Dinosaurs Lagosuchia Theropoda Sauropodamorpha Ornithischia Protoavia Aves (Birds)
Herrerasauria Ceratosauria:
Coelophysoidea
Ceratosauroidea
Abelisauroidea???
Carnosauria Megalosauroidea Allosauroidea "Coelurosauria" Tyrannosauria Ornithomimosauria Troodontia

Author's note: these pages were written some years ago. I am not planning to update them. For a more current coverage, see the link to palaeos com Palaeos website (to which many links on these pages point to anyway. More info here

Order Theropoda

Sinraptor dongi

Sauropodamorpha.  Theropods are bipedal carnivorous dinosaurs, with bird-like legs and necks. Theropoda means "beast-feet", a rather inappropriate name; "bird(-like) feet" would have been better.  Included in this group are both small forms (among them the ancestors of birds) and large predators such as Allosaurus and Tyrannosaurus.

Like the Prosauropods and the Ornithischians, Theropods evolved from lagosuchian ornithodirans, perhaps some time in the early or middle link to palaeos com Carnian.  The most primitive type, and most certainly ancestral to the other theropods, are the Herrerasaurs. From such ancestral forms Theropods diverged into Ceratosaur and Megalosaurian types during the l link to palaeos com ater Triassic, Allosaurians during the link to palaeos com early Jurassic, and finally more advanced types during the earliest Cretaceous, following the Tithonian mass-extinction (some suggest these advanced Cretaceous meat-eating dinosaurs appeared during the Jurassic, but Jurasisc remains attributed to them are mostly isolated teeth). All Theropods retained the basic bipedal carnivorore form, but still they evolved into a huge diversity of different types, in different shapes and sizes, the most spectacular of all being the birds and bird-dinosaurs. However, as Dr Tom Holtz points out, "Theropod dinosaurs (bipedal, primarily carnivorous forms) have received widespread attention in recent years owing to their importance in understanding the origin of birds.  However, the evolution of theropods was more than a "bird factory": Indeed, these dinosaurs represent one of the most successful radiations of terrestrial predators in Earth history." Tom Holtz,  1998; 1276. ("Spinosaurs as Crocodile Mimics")


Two Types Of Theropod Dinosaurs

Until recent years, the theropod or meat- eating dinosaurs were divided according to size: the small agile forms were called Coelurosaurs ("hollow- tailed saurians"), ancestral to the birds; and the large to gigantic predators, such as Megalosaurus, Allosaurus, and Tyrannosaurus, were called Carnosaurs ("flesh(-eating) saurians"), which group evolved from early Coelurosaurs.

This clear-cut distinction was upset in the 1960s and 70s by the discovery of unusual medium-sized theropod dinosaurs such as Deinonychus, and more recently several paleontologists pointed out that some coelurosaurs were more similar in structure, and hence more closely related to, certain carnosaurs than they were to other coelurosaurs, and vice- versa.  They suggested that the coelurosaur- carnosaur distinction be scrapped, and in its stead theropod dinosaurs be divided into primitive forms (Ceratosauria), and more advanced and bird-like forms, (Tetanurae). Yet even this clasisfication is simplistic, for there are a number of forms, whcih I have refferred to as "Megalosaurs", which do not fit easily into one or the other of these camps, being in a real sense transitional between the two


Giant Theropods

Big is beautiful, at least in the dinosaur world. Time and again, little ancestors evolve into great big descendants.  Every line of theropods has its giants; in the late Jurassic period (the time of the great brontosaurs and their kin) no less than four groups - the Ceratosauridae, Megalosauridae, Eustreptospondylidae, and Allosauridae - all included great predators; 10 to 14 metres in length and 3 to 6 tonnes or so in weight (the size of a fully-grown elephant) Packs of these giant meat-eaters were the only creatures big enough and fierce enough to bring down a full-grown sauropod.

During the early to mid Cretaceous there were other similarly sized giant types - the slender Spinosaurs - and several parallel lines of allosaurs - Acrocanthosaurs, Chilantosaurs, Cacharodontosaurs, Giganotosaurs, and Bahariasaurs.

And during the late Cretaceous there appeared the Tyrannosaurs, the last and perhaps the most formidable of all the theropods.  Yet these evolved not from the giant allosaurs but from small coelurosaur-sized forms.  So it seems that the small ancestor evolves into small and large descendants; the large forms rule the Earth for a while and then die out, while the small ones give rise in turn to large and small descendants.



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Parent Taxa


Class Wikipedia link Reptilia / link to palaeos com Sauropsida
Subclass Diapsida
Infraclass link to palaeos com Archosauria
Superorder: Dinosauria
Order Theropoda

for daughter taxa see below:

The Diversity of Theropod Dinosaurs

Note: the following classification is a based largely on a linneanisation of the standard dinosaurian cladograms, of which a number of examples can be found on the Web. Being Linnean it presents a more "horizontal" picture, which I feel better illustrates the diversity of these long-lived parallel lineages then a confusing forest of cladistic branches, useful as the latter may be to tracing ancestry. Dinosaurian types, like other organisms, radiated very rapidly (within the space of only a few million years), then the various lineages lived alongside each other for many tens of millions of years. Apart from Gregory Paul's superb book, there is however no recent update of the venerable Linnean arrangement; all recent adaptations being clumsy cladistic-based ones that don't work, due to the incmpatability of the cladistic and linnean systems. So I have decided to provide one here. Please do not confuse this work for the work of a specialist, I am an armchair philospher and this material is not peer-reviewed!

I have first of all elevated the Theropods from suborder to the rank of Order (but not superorder, which Gregory Paul gives the them). This order is then divided into six suborders. The emphasis is on evolutionary distinctness (like the orders of mammals). These suborders are


The following suborders I consider belonging to the dino-protobird order Protoavia. However the dividing line between theropods and birds is so fine that these can equally be considered either.

The arrangement presented here is by its intrinsic nature very tentative.  Some of these families are based on a single genus or species and so may not be valid.  A question mark or several after the name indicates uncertainty as to its placement within the larger group.  The more question marks the more uncertainty!



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Herrerasauria

HerrerasauriaThese medium-sized hunters are the earliest 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 external link  link to palaeos com Saturnalia seems to confirm this.


family Eoraptoridae
family Staurikosauridae
family Herrerasauriodea
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Suborder Ceratosauria

CeratosaurThe Ceratosaurs are the earliest and most primitive theropods proper.  They often feature unusual crests on their head, probably a device for intraspecific rivalry or mating.  They seem to have become extinct during the end Jurassic, although if abelisaurs are Ceratosaurs (and this is generally stated but still not certain), than these animals survived in link to palaeos com Gondwanaland right until the end of the age of dinosaurs.


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Suborder Carnosauria

I would like to emphasise I am using the term Carnosauria is the broad, and mostly Linnean/Evolutionary Systematic sense here. By Carnosauria I mean a paraphyletic group of mostly large (although there were also some small forms) Jurassic to Middle Cretaceous (or Late Cretaceous if one includes the Abelisaurs) theropods. There are two clear superfamilies, the Megalosauroidea/Torvosauroidea and the Allosauroidea. These represent an evolutionary succession, with some forms transitional between the Megalosaur and Allosaur grade.

Superfamily Megalosauroidea (= Torvosauroidea)

MegalosaursThe Megalosaurs are a paraphyletic taxon - they occupy a transitional position between the Ceratosaurs and the Allosaurian Tetanurae. These large carnivores remained the top preditor for many millions of years of the Middle Jurassic period, before being supplanted by the Allosaurs. However, a semi-aquatic branch, the Spinosaurs, continued well into the Cretaceous. It is also possible that Abelisaurs may be a line of late-persisting primitive megalosaurs, although this is not certain


Superfamily Megalosauroidea/Torvosauroidea
family
Megalosauridae (=Torvosauridae)
family Spinosauridae
family Eustreptospondylidae

Superfamily Abelisauroidea???
family Abelisauridae
family Noasauridae
family Velocisauridae

Clade Tetanurae

(advanced theropods and birds)

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).


Cladistically speaking, birds are theropods and dinosaurs (I can never feel comfortable with this definition), and the clade Tetanurae includes both birds and the most famous of classic theropods, although in some classifications the term would seem to relate to Tetaneuran theropods alone. 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 technical anatomical characteristics, which indicate all evolved from a single common ancestor. Tetanurans are generally subdivided into two clades, the Carnosauria (here, suborder "Allosauria") and the Coelurosauria (here, all other tetaneurans). The characteristics are listed in the following cladogram by Professor Paul Olsen

Theropod cladogram 1. three-toed foot
2. digits IV and V lost on hand
3. long arms
4. semilunate carpal
5. fused pelvis
6. large hole in lacrimal bone in skull
7. ?no unique derived characters?
8. giant, hook-like claw on digit II of pes
9. flight feathers

As can be seen, the Coelurosauria are divided into a large number of forms, some of the primitive members of which seem to have no easily identifiable characteristics (these are the ones I refer to here as general basal coelurosaurs). Many of the most interesting theropods belong to a clade called the Arctometatarsalia (in bold in the above diagram)


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Superfamily Allosauroidea

Allosaurs The Allosaurs were one of the two groups that evolved from the Megalosaurs, the other being the "Coelurosaurs".  These were large to gigantic meat-eating forms, which were the dominant carnivores from the middle Jurassic to the mid Cretaceous.

The following families can be postulated:


family Sinraptoridae
family Allosauridae
family Carcharodontosauridae
family Ornitholestidae?

Note that the Ornitholestidae are also considered Coelurosaurs (the systematics of basal tetaneurae and avetheropods is still uncertain, owing to the fragmentary nature of many Jurasisc forms

Allosaurs were most diverse and succesful during the late Jurassic and early to mid Cretaceous. They seem to have died out during the later Cretaceous (possibly the Cenomanian turnover), being suplanted by Tyrannosaurs in the link to palaeos com Asiamerican landmass, and Abelisaurs in link to palaeos com Gondwanaland.


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Suborder Coelurosauria

"Coelurosauria" means a number of different things. Originally it referred to small as opposed to large theropods - everything from Coelophysis to Ornithomimus - but this is now known to be an artificial, polyphyletic grouping group. The popular cladistic meaning is the monophyletic taxon that encompasses all advanced theropods, as well as their descendants the birds (beginning with Archaeopteryx).  The terms Maniraptoria and Maniraptoriformes (refering to the grasping hands of many of these small advanced theropods) are approximately equivalent, although referring to slightly more specialised forms. The characteristics of the coelurosaurs in relation to other theropods are listed in the following cladogram by Professor Paul Olsen

Theropod cladogram 1. three-toed foot
2. digits IV and V lost on hand
3. long arms
4. semilunate carpal
5. fused pelvis
6. large hole in lacrimal bone in skull
7. ?no unique derived characters?
8. giant, hook-like claw on digit II of pes
9. flight feathers
10. ?no unique derived characters?
11. proximal half of metatarsal of digit III pinched

As can be seen, the Coelurosauria are divided into a large number of forms, some of the primitive members of which seem to have no easily identifiable characteristics (these are the ones I refer to here as general basal coelurosaurs). Many of the most interesting theropods belong to a clade called the Arctometatarsalia (in bold in the above diagram)

As I use the term here, "Suborder Coelurosauria" is a sort of convenient "waste-basket" taxon for basal or primitive members of the clade Coelurosauria, as distinct from advanced Maniraptors, Birds, and Arctometatarsalia. The advanced maniraptors I place in a distinct order, the Protoaves. I feel Greg Paul makes a very good case in considering many of these advanced theropods are actually lineages of protobirds. However, to follow him in putting late Jurassic forms like Compsognathus and Coelurus in suborders of their own seems to involve too much taxonomic inflation, and further discoveries are necessary before we have a better understanding of the evolutionary relationships of these animals.


family Coeluridae
family Compsognathidae
family Ornitholestidae?
family Deltadromidae??
family Dryptosauridae??

The last two families are fairly large, "carnosaur"-sized animals, but seem to retain basal coelurosaur features


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Clade Arctometatarsalia

These three groups of seemingly disimiliar advanced dinosaurs share a common ankle structure and, if this structure evolved only once, would then be related, descending from an ancestor who possessed that characteristic.  Once again, Professor Paul Olsen provides a very clear cladogram showing the distinctive characteristics

Arctometatarsalia cladogram 1. proximal half of metatarsal of digit III pinched
2. enlarged brain and eyes and reduced teeth
3. metacarpals of nearly equal length
4. teeth with large denticles
5. highly reduced forelimbs and large size

Of course, there is still no guarantee that an Arctometatarsalian common ancestor ever existed, as the arctometatarsalian condition may have evolved indepoendently several times. In his wonderful phylogenetic site, Mikko Haaramo presents two rival Coelurosauria cladograms, one that external link includes the Arctometatarsalia, and another external link that doesnt.

In any case, I consider the three clades here to be three distinct suborders. Even if they did evolve from a shared common ancestor, the initial radiation was very rapid, and they soon diverged into completely different and dissimiliar forms


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Suborder Tyrannosauria

the TyrannosaursThe Tyrannosaurs were originally included under the Carnosauria but are now known to be closer to birds in their evolutionary relationships. Although technically members of the Clade Coelurosauria they are morphologically so distinct, and indeed have been since their appearance in the early Cretaceous, that they deserve their own subordinal status. They are easily recognisable by their gigantic size, huge powerful heads, large hind legs (indicating an active running ability), relatively short (for a theropod) tail, and especially the ridiculously tiny two-toed forelimbs. In contrast, all other clade coelurosauria were mostly small to medium-sized, and had small to medium-sized heads, long tails, and large grasping fore-arms. A few little-known Jurassic forms are very tentatively assigned to the Tyrannosauroidea, but I am sceptical about this. It is more likely that the Tyrannosaurs evolved as part of great late-Tithionian/early Berrisian theropodian and avian radiation that followed the Tithonian extinction event, and these Jurassic forms independently evolved certain skeletal characteristics. Tyrannosaurs are completely confined to the Cretaceous link to palaeos com Asiamerican island landmass

Superfamily Tyrannosauroidea
family Tyrannosauridae
subfamily Aublysodontinae
subfamily Tyrannosaurinae

Suborder Troodontia

TroodontThese small large-brained hunters were superficially very similiar to the Dromaeasaur protobirds. They even had a similiar sickle-claw on the same toe, although certain other features set them apart. They had unusually large eyes, and were probably nocturnal, feeding on Cretaceous mammals and other small animals.



family Troodontidae

Ornithomimosauria

OrnithomimosaurThe "ostrich dinosaurs" are among the most amazing of the many strange Cretaceous theropods and proto-birds. Apart from the typically reptilian tail, they were for the most part almost identical in size and build to ostriches, and probably lived a very similiar lifestyle. Thse were successful animals, and formed a characteristic part of the link to palaeos com Asiamerican late Cretaceous fauna. A possible ornithomimid has been described from Australia, on the basis of two isolated limbb-bones, but I wouldn't be surprised if these turn out to belong to a different animal.


family Harpymimidae
family Garudimimidae
family Deinocheiridae?
family Ornithomimidae

The remaining groups of dinosaurs are so bird-like they can equally be considered birds as well as theropod dinosaurs. They are considered here among the Protobirds.


Protobird Dinosaurs

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printed material Links Web links

Professor Paul Eric Olsen, The Real Jurassic Park - Morrison and Tendaguru Formations

Professor Paul Eric Olsen, Lecture 20 - The Early Cretaceous - Europe, the Cloverly Formation, Montana, Mongolia and North China

links link to palaeos com Theropoda - Palaeos

Jurassic Gallery Jurassic Gallery - fantastic artwork by M. Shiraishi, includes reconstructions of many dinosaurs. By Japanese and English


books Books and CD Roms CD Roms

In Association with Amazon.com

CD Rom Walking With Dinosaurs - if you haven't seen this magnificent series you are doing yourself a disservice. Makes Jurassic Park look like amateurs.

CD Rom Allosaurus - A Walking With Dinosaurs Special The life and times of Big Al

printed reference Gregory S. Paul, Predatory Dinosaurs of the World Simon and Schuster, 1988

more Dinosaur books


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