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The D-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when Tyrannosaurus bit and pulled.
The remaining teeth were robust, like "lethal bananas" rather than daggers, more widely spaced and also had reinforcing ridges.
Because all known skin impressions from larger tyrannosauroids known at the time showed evidence of scales, the researchers who studied Dilong speculated that feathers may correlate negatively with body size—that juveniles may have been feathered, then shed the feathers and expressed only scales as the animal became larger and no longer needed insulation to stay warm.
others, such as Yutyrannus huali (which was up to 9 meters (30 ft) long and weighed about 1,400 kilograms (3,100 lb)), preserve feathers on various sections of the body, strongly suggesting that its whole body was covered in feathers.
(2011) found that the maximum weight of Sue, the largest complete Tyrannosaurus specimen, was between 9.5 and 18.5 metric tons (9.3–18.2 long tons; 10.5–20.4 short tons), though the authors stated that their upper and lower estimates were based on models with wide error bars and that they "consider [them] to be too skinny, too fat, or too disproportionate" and provided a mean estimate at 14 metric tons (15.4 short tons) for this specimen. (2009) tested dinosaur mass estimation procedures on elephants and concluded that those of dinosaurs are flawed and produce over-estimations; thus, the weight of Tyrannosaurus, as well as other dinosaurs, could have been much less.
Due to the relatively small number of recovered specimens and the large population of individuals present at any given time when Tyrannosaurus was alive, there could have easily been larger specimens than those currently known including "Sue", though discovery of these largest individuals may be forever untenable due to the incomplete nature of the fossil record.
But in other respects Tyrannosaurus's skull was significantly different from those of large non-tyrannosauroid theropods.
The largest found so far is estimated to have been 30.5 centimeters (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found. Mark Norell of the American Museum of Natural History summarized the balance of evidence by stating that: "we have as much evidence that T.
rex was feathered, at least during some stage of its life, as we do that australopithecines like Lucy had hair." The first evidence for feathers in tyrannosauroids came from the small species Dilong paradoxus, found in the Yixian Formation of China, and reported in 2004.
As with many other theropods discovered in the Yixian, the fossil skeleton was preserved with a coat of filamentous structures which are commonly recognized as the precursors of feathers.
In contrast the hind limbs were among the longest in proportion to body size of any theropod.
The tail was heavy and long, sometimes containing over forty vertebrae, in order to balance the massive head and torso.By far the largest carnivore in its environment, Tyrannosaurus rex was most likely an apex predator, preying upon hadrosaurs, armoured herbivores like ceratopsians and ankylosaurs, and possibly sauropods.