Altirhinus was herbivorous and bipedal when walking or running, but probably became quadrupedal when feeding from the ground. According to the original description, the entire body probably extended 8 m from snout to tail tip. In 2010, Gregory S. Paul estimated the length at 6.5 metres (21 ft), the weight at 1.1 tonnes. The skull alone is about 760 mm long, with a wide mouth and a distinctive tall arch on top of its snout, from which this dinosaur derives its name.