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Tyrannosauroidea
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Tyrannosauroids ("tyrant lizard like") were a superfamily of carnivorous dinosaurs. This group includes the family tyrannosauridae, which in turn includes the well-known giant tyrannosaurs, like Tyrannosaurus rex. This entry will deal primarily with the more basal ("primitive") members of the tyrannosaur line.
Contents
- 1 Classification and definition
- 2 Description
- 3 List of Species
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Classification and definition
The superfamily Tyrannosauroidea was first named by Henry Fairfield Osborn in 1905. In modern paleontological research of dinosaurs, such taxon ranks are rarely used. An exact cladistic definition of Tyrannosauroidea was first given by Paul Sereno in 1998: Tyrannosaurus rex and all species more closely related to Tyrannosaurus than to modern birds. In 2004, Thomas Holtz proposed a potentially more restrictive definition: Tyrannosaurus rex and those species more closely related to Tyrannosaurus than to Deinonychus, Ornithomimus, or Allosaurus [1].
Description
Tyrannosauroids are characterized mainly by shared skeletal structures, especially the distinctive strucure of their hip bones and the fusion of nasal bones. Early tyrannosauroids lacked the characteristic broad, massive skulls and reduced arms of their more advanced relatives. These early species typically had medium to small sized skulls relative to their body size, a more lightweight, gracile build, and long, three-fingered arms. Most lacked the distinctive banana-shaped (D-shaped in cross section) teeth of the tyrannosaurids. At least superficially, they would have appeared more like "
coelurids" than as later tyrannosaurs. Some researchers suggest that some or all of the known "coelurids" may actually be early tyrannosauroids, though a rigorous study has yet to be performed to refute/support this idea
[2].
Note: The above applies to all tyrannosauroids, including tyrannosaurids. Earlier tyrannosauroids were generally small and lived between the mid-late Jurassic period and the Early Cretaceous, although some primitive tyrannosauroids (such as Dryptosaurus) survived into the Late Cretaceous.
Feathers
The only known skin impressions from an early tyrannosauroid come from a fossil of Dilong paradoxus. It shows a full covering of simple feathers with a two-branched structure similar to the feathers of a modern kiwi and the related dinosaur Sinosauropteryx. While no other skin impressions are known from the basal members of this group, it is likely that at least the smaller species all had a similar coat of feathers.
Crests
At least one species of early tyrannosauroid, Guanlong, bore a delicate bony crest on the head. Some theropods like Proceratosaurus and Monolophosaurus, had similar cranial ornamentation.
List of Species
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