According to Mark Norell of the American Museum of Natural History in New York, another member of the team that worked on the two new dinosaurs, "Xiongguanlong sheds light on the missing 40 to 50 million years of tyrannosaur evolution." Xiongguanlong is unusual among tyrannosaurs in having a very long and narrow snout, rather than a wide, massive skull optimized for powerful biting as is seen in T.rex. Despite this difference, Xionguanlong does mark the earliest appearance of several hallmark traits of larger, geologically younger tyrannosaurs, including a short, broad braincase, broad struts of bone near the temples, expanded areas for jaw muscle attachment on the skull roof, modified "nipping" teeth at the front of the mouth, and expanded vertebral structures to support a large head. Many of these features represent structural modifications for increasing bite forces and presage the specialized skulls of larger tyrannosaurs.
Norell notes that "Xiongguanlong underscores that tyrannosaurs started as small to mid-sized predators, but a number of the traits related to the enormous bite forces of T. rex were already evident at this relatively early stage of tyrannosaur evolution."
Adds Makovicky, "The proportions of Xiongguanlong's skull are similar to those of juveniles of large tyrannosaurs, confirming that massive skulls of T.rex and its closest relatives evolved from animlas with long slender snouts like Xiongguanlong."
Second find: A giant "ostrich-mimic"
The team also discovered three specimens of a remarkable, second theropod from the Yujingzi basin during the 2006 and 2007 field seasons. Beishanlong grandis (bay-SHAN-long gran-DIS) is a new species of ornithomimosaur, or ostrich-mimic dinosaur. Ornithomim
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