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Tyrannosaurus Anatomy |
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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!
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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. |
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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. |
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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.
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Edugraphics.Net | Feenixx Publishing |
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