HOME PAGE
 Eras of Life
 Dinosaur Evolution
 Feathered Dinosaurs
 Tyrannosaurs

Ancestors

  Introduction
  Herrerasaurus
  Eoraptor
  Coelophysis
  Eustreptospondylus

Species  

  Albertosaurus
  Alectrosaurus
  Alioramus
  Daspletosaurus
  Dilong
  Eotyrannus
  Gorgosaurus
  Nanotyrannus
  Tarbosaurus
  Tyrannosaurus
  Other Tyrannosaurs

New Discovery

  Guanlong Wucaii

Information

   Anatomy
   Hunter v Scavenger
   Family Life
   Growth Rate
   Exhibits
 Weird Dinosaurs
 Prehistoric Sea Monsters
 Pterosaurs
 Sauropods

 

 

Tyrannosaurus Anatomy

    The reason why the arms of the large meat-eating dinosaurs like Tarbosaurus are so small is a mystery. Some paleontologists believe that the reduced weight of the arms helped these animals to keep their balance on two legs in spite of their having such very large heads. The head (and jaws) were used for attacking prey, but did not contain a large brain—in fact, it has been calculated that Tarbosaurus had a brain only one tenth of the size of what would be expected in a mammal!

    In the March 2005 Science magazine, Mary Higby Schweitzer of North Carolina State University and colleagues announced the recovery of soft tissue from the marrow cavity of a fossilized leg bone from a 68-million-year-old T. Rex. The bone had been intentionally, though reluctantly, broken for shipping, and then not preserved in the normal manner specifically because Schweitzer was hoping to test it for soft tissue. Designated as the Museum of the Rockies specimen 1125, or MOR 1125, the dinosaur was previously excavated from the Hell Creek Formation. Flexible, bifurcating blood vessels and fibrous but elastic bone matrix tissue were recognized. In addition, microstructures resembling blood cells were found inside the matrix and vessels. The structures bear resemblance to ostrich blood cells and vessels. However, since an unknown process distinct from normal fossilization seems to have preserved the material, the researchers are being careful not to claim that it is original material from the dinosaur. The presence of medullary bones in this specimen is also of interest.
     From the mid-1990s on, feathered tyrannosaurs were a controversial subject; for example, the reaction to a depiction of a downy T. rex chick in the November 1999 issue of National Geographic Magazine. But now, at least some tyrannosaurids appear to have been feathered. Small coelurosaurs from the Yixian Formation in Liaoning, China, have been discovered with either pennaceous feathers or fur-like "protofeathers", which suggested the possibility that tyrannosaurids may also have borne feathers as well. In 2004, the primitive tyrannosaurid Dilong paradoxus was discovered from the same formation with preserved long tail plumes. However, (adult) tyrannosaurs in Alberta and Mongolia have skin impressions which appear to show the pebbly scales typical of other dinosaurs. It is possible that tyrannosaurs lost their feathers as they grew, similar to the hair density of an elephant as it grows, or were only feathered on parts of their bodies. In general, small animals need insulation more than large ones because of their proportionately larger surface areas.
especially their large, serrated teeth, which they shed periodically like most archosaurs.  The teeth of tyrannosaurids are very interesting — rather than being the flat knifelike blades as in most other carnivorous dinosaurs, they are, as Berkeley's Professor Kevin Padian describes them, "like lethal bananas;" more like giant spikes than razor-edged blades. With a mouthful of this murderous fruitlike dentition, tyrannosaurs had a whopping bite, which might have made up for their reduced forelimbs. The bite marks of these teeth are quite recognizable on some dinosaur bones. Some tyrannosaur fossils show evidence of bite marks from other tyrannosaurids, suggesting that there might have been fierce fighting between tyrannosaurs, or even cannibalism.