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

Superfamily Tyrannosauroidea

The formidable Tyrannosaurus rex

from Walking with Dinosaurs © 1999 ABC, BBC

Considering the various lines of theropods, it is interesting that the most primitive forms have very long tails, long bodies, relatively small heads, short hind legs, and relatively large forelimbs.  The later and more advanced types had relatively shorter bodies and tails, larger heads, larger hind legs, and (in the case of the giant forms) smaller and smaller forelimbs.   This evolutionary trend reaches its culmination in the Tyrannosauridae of the the late Cretaceous of the Asiamerican landmass.

At this time a narrow north-south seaway divided what is now North America into two large islands; the same thing happened in Asia.  But a land-bridge linked east Asia (Mongolia, China, etc) with western North America.  Apart from one very primitive form from India (then an island), it was only on this Cretaceous continent, called " Asiamerica", that Tyrannosaurs are found .

Although old drawings of Tyrannosaurus rex give the beast an almost erect stance and a long reptilian tail, this is now known to be incorrect.   The back was held horizontally, as in other theropods (although the animal  could obviously rear up when the situation required); and the tyrannosaur tail was, as a proportion of overall length, the shortest of any large theropod.  The fearsome eagle-taloned feet of the tyrannosaurs are also a myth; the claws on the hind feet were short, rounded, and hoof-like.  All the killing was done by the huge jaws with their array of 15-centimetre steak-knife- like teeth.  The power of these jaws was incredible.  Think of a huge terrestrial Great White shark.  The animal could bite out a wound a metre long and well over thirty centimetres deep and wide.  Yet only with such ferocity could it possibly take on its main prey, the elephant-sized horned dinosaur Triceratops.

One thing that is quite bizarre about the tyrannosaurs are their tiny little forelegs.  These actually became smaller and smaller as the creatures evolved.  The famous Tyrannosaurus rex, the last and most advanced of the tyrannosaurs, had the smallest forelimbs (proportionally speaking) of any dinosaur, and it is likely that if their evolution had not been cut short by the terminal Mesozoic catastrophe they would have lost their arms altogether.  Like ground-living large running birds, the big theropods really had no use for their forelimbs.  They acted more like huge flightless birds of prey, than the overgrown bipedal lizards of popular imagination.

Interestingly, after the extinction of the dinosaurs, a number of real flightless birds - Diatryma, Phorusrhacos, etc - took over the ecological niche of the theropods, becoming huge-headed, fast-running predators, 1.5 to 2 metres or more in height.

This family was coined by Greg Paul to refer to small Jurassic theropods with similar hips. It has been suggested that they are on the lineage of ancestry to the tyrannosaurs.

Iliosuchus incognitus Huene, 1932

Comments: The ilia (upper hip bone) of this tiny dinosaur have a distinctive vertical ridge on the outside surface, similar to Stokesosaurus. This same condition is also found in the tyrannosaurs, suggesting that this animal may be the earliest known Arctometatarsalian (the clade that includes Tyrannosaurs and Ornithomimosaurs). However, more remains would need to be recovered to be certain

Stokesosaurus clevelandi

Comments: All specimens were recovered from the same quarry but there is no guarantee they are from the same animal. The hip-bones (ilia) are the main remains, have a distinctive vertical ridge, and resemble those of Iliosuchus, for a while the two being synomised (by Peter Galton) in the same genus. A similar pelvis has been found in Portugal. James Madsen tentatively refered this animal to the Tyrannosauridae due to a number of similarities in the ilum, braincase and premaxilla. Paul considers the similarities of Stokesosaurus too few to justify inclusion among the tyrannosaurs. Holtz places the genus in the Tyrannosauroidea and relates it to Itemerus. It has been suggested that this animal may be the adult form of Coelurus.

Tom Holtz considers Itemirus to be probably related to Stokesosaurus. If so it probably belongs to a separate family, as this genus is seperated by some tens of millions of years. In all probablity there were a number of tyrannosaurian and dromaeosaurian type theropods evolving in parallel throughout the early and middle Cretaceous.

Itemirus medullaris Kurzanov 1976

Comments: based on an unusual braincase that shares features with Stokesosaurus, tyrannosaurids and dromaeosaurids

If this is not yet a distinct family it should be! These animals were the ancestors of the the Tyrannosauridae. So far there is only one definitely known species, but it is not unlikely that other poorly known Cretaceous theropods may belong here as well.

Eotyrannus lengi Hutt, Naish, Martill, Barker, and Newberry, 2001

Comments: A lightly built and obviously agile animal, similar to both Tyrannosaurus and Deinonychus in form, and clearly related to the latter in the form of the skull. Unlike its giant descendents, it still retained large arms. This newly discovered form represents the most completely known Cretaceous European theropod

Tyrannosaurids are often divided into two subfamilies: the small primitive aublysodontines and the large tyrannosaurines, but the fragmentary material of the former means they might not consitute a valid taxon. In fact Aubylson is almost certainly a mis-interpretation of juvenile tyrannosaurine material. All are known only from fragmentary remains. They are based almost entirely on distinctive nonserrated and ridged premaxilla teeth (in the front of the jaw). It has been plausibly argued that the teeth are just typical teeth of young tyrannosaurids. Further, whilst Aublysodon-like teeth are fairly common and found in practically all horizons where tyrannosaurid body fossils are found, not one adult theropod skull is known from North America with such a tooth actually in place in a premaxilla. The best-known Aubylsodont, the so-called "Jordan theropod" (Aublysodon molnari Paul, 1988c, = Stygivenator molnari Olshevsky, 1995), actually just a snout with some teeth, has been variously interpreted as Aublysodontine (Paul, Holtz), dromaeosaurid, and tyrannosaurid, but is most likely a juvenile (length about 3.8 meters, weight around 200 kg) specimen of T. rex.

Family Tyrannosauridae Osborn 1906
technical diagnosis: see Palaeos
Guild/Ecological niche: Gigantic terrestrial carnivore
Modern equivalent: none
Time: Late Cretaceous
Distribution: Asiamerica only
Ecological community: Hadrosaur-Ceratopsian
Evolved from: Eotyrannidae
Replaced: Allosauridae
Replaced by: none
Extinction because of: K-T mass extinction event
Descendents: none
Linnean status: valid family (listed at Zoological Record Systematic Thesaurus - Reptilia)
Cladistic status: monophyletic
Parent clade: Arctometatarsalia
Adult length: 6 to 14 meters
Adult weight: 500 kg to 7 tonnes
Habitat: floodplain, uplands
Diet / Preferred food: other dinosaurs, any tetrapods smaller than themselves
Hunting/Food gathering/Foraging/Feeding habitat/Feeding behaviour: ambush?
Food Processing mode: small prey swallowed whole, larger animals probably eaten in chunks
Movement: bipedal, active on land, adequate swimmers
Predators: none (top of food chain)

Subfamily "Alectrosaurinae"

Alectrosaurus is included by Tom Holtz under the Aublysodontinae, but since the Aublysodontinae is better considered as juvenile Tyrannosaurids, this primitive genus is best placed in a subfamily of its own.

Alectrosaurus olseni Gilmore, 1933a

Comments: a rather small, primitive ancestral form. According to Paul the skull and hind-limb is quite Albertosaur-like, and he places the taxon in the subfamily Tyrannosaurinae. Holtz however includes this genus under the Aublysodontinae. A large humerus previously associated with this species was since discovered to belonged to a segnosaur

Subfamily Tyrannosaurinae

Large, robust powerful animals, these were clearly the top preditor of their environment. But for all their fame and charisma they are limited to a single landmass at the last 20 million years or so of the Cretaceous period. There would seem to be three groups or tribes, although the Albertosaurs are clearly paraphyletic.

Tribe "Alioramini"

Apologies for the made-up taxon, but this single aberrant genus clearly does not belong with either the Albertosaurs or the Tyrannosaurs.

Alioramus remotus Kurzanov, 1976

Comments: a small, primitive tyrannosaur. Distinguished by its slim and lightly built lower jaw and unusual nasal ridge (which probably supported a large crest in life) running down the midline of its skull. This animal would seem to be an early off-shoot of the main Tyrannosaur lineage

Tribe Albertosaurini

Although the Albertosaurs are frequently now considered three different genera, this overemphasises the differences between these clearly closely related animals. All three of them could easily belong as different species to the same genus, Albertosaurus. However, Daspletosaurus can equally be located among the Tyrannosaurines. All these animals are characterised by a small horn in front of above each eye (on the preorbital bone). Greg Paul distinguishes a gracile Albertosaur lineage from a more heavily built Tyrannosaur (including Daspletosaurus) lineage

Albertosaurus libratus Lambe, 1914c

Comments: Perhaps the best known Tyrannosaur in terms of fossil remains. Two types of heads are known, differeing in the shape of the postorbital horn; sexual dimorphism seems more likely than two species. Originally named Gorgosaurus, it was later (because of the poor quality of the Gorgosaurus type material) renamed Albertosaurus (by Dale Russell in a famous paper). Now, because of the ambiguity of the type material of Albertosaurus, Gorgosaurus has once again been separated. Yet the difference between this animal and the early Maastrichtian Albertosaurus sarcophagus are minor. Most dinosaurologists have kept this species in Gorgosaurus because of phylogenetic uncertainties; is it closer to A. sarcophagus or to Tyrannosaurus? Personally I find this abundance of generic names for very similar animals misleading; as one who adopts a Linnean (well, Evolutionary Systemmatist) rather than a Cladistic approach, I would rather keep libratus in Albertosaurus. But I may be completely wrong. This is a characteristic index fossil, more common than its more heavily built contemporary Daspletosaurus, and one can safely refer gracile late Campanian albertosaur remains from Alberta to this species.

Albertosaurus sternbergi, a lightly built animal with huge teeth relative to skull size (the teeth are actually larger than those of adult A. libratus, although the latter is about 1 1/2 times the linear dimensions) may be either a distinct species or, much more likely, juveniles of A libratus and D. torosus.

Albertosaurus sarcophagus Osborn, 1905

Comments: Type species of Albertosaurus. Greg Paul divides this species into two, the more lightly built A. arctungus and the more heavily built A. sarcophagus. However, teh material is fragmentary for each, and it just as likely these belong to the same species. This species may have evolved from the earlier A. libratus

Tribe Tyrannosaurini

Tyrannosaur species have been organised in everywhere from a single genus to at least half a dozen. The number of valid species is also in dispute. They were huge animals, as big as elephants, and represent the culmination of late Cretaceous theropod evolution (in view of the fact that they are all extremely similar I favour the former option). Distinguishing feature of Tyrannosaurini is the large size, stocky heavy-boned build, relatively shorter (in relation to Albertosaurini) hind limbs, with the Ilium (lower leg bone) being longer than the femur (upper leg bone) and longer (although still tiny) forelimbs, shorter snout (presumably an adaptation to allow binocular vision), deep lower jaw (for more powerful bite), and (in Tyrannosaurus) lack of small hornets in front of the eyes, postorbital bosses occuring instead. For a more technical coverage of the features of this clade, see Holtz

Daspletosaurus torosus Russell, 1970a

Comments: This heavily-built animal seems to be transitional between Albertosaurs and Tyrannosaurus. An unusual feature of this animal is the length of the arms; it had the longest arms, relative to size, of any of the advanced tyrannosaur. Even so, its arms are tiny compared to, say, Allosaurus. George Olshevsky considers this species similar enough to A. libratus and A. sarcophagus to go in the same genus (Albertosaurus), whilst Tom Holtz includes it in the Tyrannosaur clade. Greg Paul goes further and makes it a subgenus of Tyrannosaurus, but this is taking "lumping" too far

New Species (Daspletosaurus sp.)

Comments: The as-yet-unnamed Two Medicine tyrannosaurid, which will no doubt be given a new generic name, is described as a transitional form between the Daspletosaurus and Tyrannosaurus. But since Tyrannosaurus had already evolved in Asia, it is unlikely to be an ancestor of that genus. It retains a low lacrimal horn, typical of Albertosaurus and Daspletosaurus. This species seems to be the last of the big indigenous american tyrannosaurs. With the drop in sea level during the late Maastrichtian that allowed Alamosauriian titanosaurs to wonder up from South America, Tyrannosaurus tyrannosaurids and Saurolophus hadrosaurids were able to cross the land-bridge from Asia. Since T. rex is the only big preditor in late Maastrichtian Western north America, it seems this large descendent of T. bataar simply pushed the local tyrannosaurs into extinction.

Tyrannosaurus efremovi Maleev, 1955a

Comments: The type species of Tarbosaurus. This animal clearly belongs under the genus Tyrannosaurus, and it is only the annoying tendency of vertebrate paleontolgists to give every new discovery a new generic name that results in them being considered distinct. The smaller size may be due to the harsher drier conditions in which this animal lived. In addition, this smaller animal may have been the "panther" to the T. bataar "lion", the two animals co-existing but going after different types of game, like Albertosaurs and Daspletosaurs in Western North America. This species lived in Mongolia (part of the same large island-continent as Western North America but seperated by straits) at the same time as Albertosaurus and Daspletosaurus lived in America.

Maleevosaurus novojilovi Carpenter, 1992 (originally Gorgosaurus novojilovi Maleev, 1955b) known only from a small partial skull, was originally considered a seperate species, but is more plausibly synonymised with Tarbosaurus efremovi or T. bataar, as a juvenile.

Tyrannosaurus bataar Maleev, 1955a

Comments: Given the wonderful generic name Jenghizkhan (after the Mongol conquerer Genghis Khan). Unfortunately, this is certainly just another (albeit very large) species of Tyrannosaurus; the additional generic splitting is uneccesary. Distinguished from the contemporary T. efremovi by its huge size, massively constructed and rugose skull elements, and unusually tall neural arches (the tallest relative to diameter of any Tyrannosaur. This animal is so similar to Tyrannosaurus rex that it is very difficult to distinguish the two. Sometimes synomised with T. efremovi. For more, see the DinoData page on JENGHIZKHAN

Tyrannosaurus luanchuanensis (Dong,1979)

Comments: the date is given conventionally as Late Campanian, but if this is a Tyrannosaurus it is more likely to be early or middle Maastrichtian

Tyrannosaurus rex Osborn, 1905

Comments: One of the famous prehistoric animals of all time, it is also the largest member of the family, and one of the largest theropods. It probably was a fairly fast animal for its size (most large animals move very slowly), but not neraly as fast as Bakker and others have claimed. T. rex was very heavily built with powerful jaws and 15 cm serrated teeth. The suggestion it (and its relatives) were shudffling scavangers, popular for a while some ten or twenty years ago, seems to me patently absurd. Like all large tehropods, this animal was clearly in its form an active hunter.

Albertosaurus megagracilis Paul, 1988, renamed Dinotyrannus megagracilis by Olshevsky, 1995, has been considered a late Albertosaur due to its light build. It is based on a single sub-adult partial skeleton. It lacks the characteristic Albertosaur lacrimal horn and is more likely to be just a sub-adult Tyrannosaurus rex.

Tyrannosaurus lancensis (Gilmore, 1946)

Comments: Variously considered a distinct genus (even from a different tribe) or a juvenile T. rex. Moved from Gorgosaurus to Albertosaurus, then Bakker et al. (1988) placed this specimen in a seperate genus, Nanotyrannus. Carr (1999), argues that this individual is most likely a juvenile T. rex. However the bones of the skull are well fused like an adult animal (according to Paul, even adult T. rex skulls are no better ossified), making it difficult to imagine how, if it was juvenile, it could have grown to full size. It may be that adult T. rexes had a huge range of individual variation of size (somerthing that is possible but perhaps not the best explanation). My own pet theory is that this represents a dwarf race, species or subspecies; possibly a forest or mountain form that had wondered down into the lowlands. The juvenile characteristics of the skull would then be neotonus features

cautionary note (please read before using this page as reference material!)

Books, DVDs and Web Links

Peer Reviewed References and Books (whether Peer Reviewed or not)

Carr, T. D. 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria, Coelurosauria). Journal of Vertebrate Paleontology 19: 497-520.

Thomas R. Holtz, Jr. 2000, 2001 Tyrannosauroidea - Tyrant dinosaurs and their possible relatives - Topmost of the Tree of Life's tyrannosaur pages. The Tree of Life is one of the very peer-reviewed (and hence "proper science" sites on the Web

Thomas R. Holtz, Jr. 2000, 2001 Tyrannosauridae - Tyrant dinosaurs - child node of the above page, technical intro to the Tyrannosauridae.

Thomas R. Holtz, Jr. 2000, Tyrannosaurid Systematics more of the above

Molnar, R. E., Kurzanov, S. M., & Dong, Z., 1990: Carnosauria. 169-209 in Weishampel, D. B., Dodson, P., & Osmólska, H. (eds.), 1990: The Dinosauria. University of California Press, Berkley, Los Angeles, Oxford, 1990

Paul, G. S. 1988. Predatory Dinosaurs of the World, Simon and Schuster, New York. 464 pp.

Russell, D. A. 1970. Tyrannosaurs from the Late Cretaceous of western Canada. National Museum National Science Publications in Palaeontology 1: 1-34.

Web Sites

Earth History Portal

Tyrannosauridae - Palaeos - detailed technical diagnosis, lots of links

Tyrannosauridae - Fred Bervoets' DinoData - lists every genus and species

Tyrannosauridae - Mikko Haaramo's phylogeny pages

Other

A Changing Look at Tyrannosaurids - Darryl Jones, very good review

Tyrannosauroidea - T. Mike Keesey's Dinosauricon, short essay and a list of every known genus in the form of a cladistic tree

Tyrannosauridae - Justin Tweet's Thescelosaurus! - good short summary of each genus and species, including poorly known forms

Tyrannosaurids - Tyrannosaurid essays

Lecture 20 Late Cretaceous - by Professor Paul Eric Olsen, part of DINOSAURS AND THE HISTORY OF LIFE - GEOLOGY V1001x

Tyrannosaurian implosion - Paleozoology & Evolution list, Message 339 - mirror - useful observations on Tyrannosaur systematics, by George Olshevsky

T. Rex Relative Discovered By Larry O'Hanlon, Discovery News (on Eotyrannus)

Death of a Dynasty - from the popular BBC TV series, available in DVD.

My phylogeny etc. (was RE: SVP review (the short version)) some short provisional notes on theropod phylogeny by Tom Holtz