The first "Bactrosaurus" remains recovered from the Iren Dabasu Formation in the Gobi Desert of China were composed of partial skeletons of six individual "B. johnsoni". The specimens collected appear to come from a variety of age groups, from individuals that may be hatchlings to full-sized adults. The fossils were described in 1933 by Charles W. Gilmore, who named the new animal "Bactrosaurus", or "club lizard", in reference to the large club-shaped neural spines projecting from some of the vertebrae. The Iren Dabasu Formation has been dated to the Cenomanian stage, around 95.8 ± 6.2 million years ago.