Bactrosaurus or “Bactrian lizard” is a genus of dinosaur from the Late Cretaceous Period (97 – 85 million years ago). It lived in what is now eastern Asia. Bactrosaurus is one of the earliest known hadrosaurs, and although it is not known from a full skeleton, it is one of the most well known early hadrosaurs, making its discovery a significant unearthing. It was first recovered from the Gobi Desert in China and Mongolia. Six individuals were found from a variety of age groups, from hatchlings to full-grown adults. The type species is B. johnsoni. The skeletal fragments found include the limbs, pelvis, and most of the skull.
Bactrosaurus as an adult would have measured 20 feet long, 6.6 feet high at the shoulder, and would have weighed about 2400 to 3300 pounds. This dinosaur had a powerful build, which was unusual for most hadrosaurs. Originally, it was believed that this dinosaur lacked a crest, but further remains that were uncovered, showed what appeared to be the base of an incomplete crest.
In 2003, evidence of cancerous tumors were discovered in fossilized Bactrosaurus skeletons. Computerized testing and screening for tumors were subsequently done on more than 10,000 fossils of other dinosaurs and the tumors were limited only to the Bactrosaurus and its closely-related genera. It is unknown exactly what may have caused these tumors, but it seems it was spread genetically.