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The Tyrant Lizards: The Tyrannosauridae

   The name says it all. This group of huge carnivores must have tyrannically ruled the land during the last part of the Cretaceous, 85 to 65 million years ago. Short but deep jaws with banana-sized sharp teeth, long hind limbs, small beady eyes, and tiny forelimbs (arms) typify a tyrannosaur. The Tyrannosauridae included such similar animals (in rough order of increasing size) as Albertosaurus, Gorgosaurus, Daspletosaurus, Tarbosaurus, and of course Tyrannosaurus rex. Tyrannosaurus rex is the world's most famous dinosaur and almost everyone is familiar with it.  Comparatively few have any knowledge of his relatives - the other members of the Tyrannosaur family. This introduces T. rex and nine of his cousins, all listed at left.  An informative caption cites name, pronunciation, size, when he lived, where fossils have been found and interesting information. 
    Informative insets explore tyrannosaur ancestors, anatomy, behavior, recent discoveries and museums where T. rex fossils may be seen.
    Dr. Phillip Currie of the Royal Tyrell Museum in Alberta, Canada was the technical consultant on this poster.  He is regards as one of the world's leading authorities on tyrannosaurs.
    Tyrant dinosaur paleobiology has been the subject of numerous technical and popular studies and speculations, due to the fact that they are known from relatively complete fossils of large to gigantic size and highly derived anatomy. Some authors (Lambe 1917, Colinvaux 1978, Halstead and Halsted 1981, Barsbold 1983, Horner and Lessem 1993, Horner 1994, Horner and Dobb 1997) have suggested that tyrannosaurids in general or Tyrannosaurus rex in particular were obligate scavengers, incapable of taking down live prey. However, Farlow (1993) and Holtz (in press c) have found these theoretical, ecological and ecomorphological arguments wanting at present. Instead, as is the case with most large-bodied terrestrial carnivores, tyrant dinosaurs probably used both scavenging and predation in order to obtain their food. Carpenter (2000) has documented an adult specimen of the hadrosaurid Edmontosaurus annectens with a bite mark attributable by morphology and stratigraphy to Tyrannosaurus rex: because this injury shows subsequent regrowth of bone, this wound was inflicted on a living animal rather than a carcass.
   Tyrannosaurid dentition is markedly heterodont, perhaps indicating a partition of different sectors of the jaw for different function: scraping for the incisiform premaxillary teeth versus tearing and crushing for the lateral teeth, for example. Despite statements to the contrary (Feduccia 1999), the dentition of tyrannosaurids is not similar to those of other theropods. Instead, the incrassate (labiolingually expanded) lateral teeth of tyrannosaurines have greater mediolateral and craniocaudal bending strength than those of other theropods (Farlow et al. 1991, Holtz in press c). Erickson and Olson (1996), Erickson et al. (1996), Molnar (2000), Hurum and Currie (2000), and Holtz (in press c) have argued on tooth mark and biomechanical evidence that tyrannosaurids were capable of producing a greater crushing bite than other large theropods, such as allosauroids and abelisaurids. A very large coprolite from the Scollard Formation, probably referable to Tyrannosaurus rex, is nearly half macerated ornithischian bone by volume (Chin et al. 1998), consistent with the crushing bite model.
   Tyrannosaurid forelimbs are extremely reduced, both in proportion to the body and in terms of digit development. In contrast, the hindlimbs of tyrant dinosaurs (and in particular the tibiae and metatarsi) are elongate compared to those of most other theropods of the same body mass. Indeed, the hindlimb proportions of tyrannosaurids, ornithomimosaurs, and the gracile ceratosaur Elaphrosaurus form a continuous allometric trend, suggesting that the tyrant dinosaurs had a greater cursorial ability than other large-bodied theropods (such as allosauroids and spinosauroids) (Holtz 1995, Carrano 1998, Paul 2000). However, Farlow et al. (1995) have calculated that at extremely high speeds an adult Tyrannosaurus rex would be subjected to fatal damage if it fell, suggesting that very large individual tyrannosaurids may not have been as cursorial as younger or smaller specimens.
   Currie (2000) reports the discovery of at least nine individuals of Albertosaurus sarcophagus from the same quarry; these were of different ontogenetic stages, suggesting that at least some tyrannosaurid taxa may have been gregarious.


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