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What more can be said about Tyrannosaurus rex, probably the single most famous stem-bird there is? Living in Late Cretaceous North America, T. rex was first described by Henry Fairfield Osborn in 1905, though it's remains were actually known since 1892, under the name Manospondylus gigas. M. gigas has historically been viewed as a dubious species, as it was named by the infamous bone warrior Edward Drinker Cope for only two vertebrae, which could have come from any gigantic late Maastrichtian age tyrannosaurines (as if there were more than one!). In 2000, Peter Larson claimed to have re-discovered Cope's dig site, and recovered what may be the rest of the holotype skeleton, which he nickneamed "E.D. Cope". As Larson pointed out, this would confirm that M. gigas is the correct name for the animal we all know as T. rex. Luckily, the ICZN has methods in place that can conserve the beloved name, and it's likely Tyrannosaurus rex will be ressurected in the future.
For a long time, T. rex was considered the largest land predator ever, although such theropods as Carcharodontosaurus, Giganotosaurus, and Spinosaurus grew larger (Spinosaurus was known to be larger since 1915, though it was not as well known due to its being collected by German scientists and the type specimen being destroyed during World War II). Much has been made of the scavenger vs. hunter debate, especially with studies showing that T. rex could not run well. It should be pointed out that younger tyrannosaurs were very good runners, and it's possible these dinosaurs hunted in packs or family groups, as evidenced by healed wounds that would have proved fatal if not for the aid of others. Also, specimens of Triceratops and Anatosaurus have been found with healed-over Tyrannosaurus bite marks. Add to this the lack of any other large predators in the environment of T. rex and the scavenger 'debate' begins to deflate.
The T. rex depicted above is more robust than in most popular illustrations. This follows the work of Bates et al. (2009). Their study can be read here. Like most other stem-birds, tyrannosaurs were likely covered in downy feathers, though their gigantic size and range that included near-tropical ecosystems may have limited their density on the body. Larger, more complex feathers may have been retained on strategic points of the body for display, as restored here on the arms.
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