The first species of the hadrosaurid dinosaur Hypacrosaurus was described in 1913 by palaeontologist Barnum Brown of the American Museum of Natural History (New York), from remains his field party had collected along the Red Deer River in Alberta in 1910.
The name Hypacrosaurus comes from Greek words meaning "nearly the highest lizard", reflecting that this dinosaur was only a little smaller than the largest carnivorous dinosaur, Tyrannosaurus rex, the "tyrant king lizard".
The species name that Brown attributed to Hypacrosaurus was altispinus, means "high spined". This refers to the extremely long neural spines of its backbone (vertebral column). These spines are the tallest amongst hadrosaurian dinosaurs.
Hypacrosaurus altispinus was about 9 m (29.5 ft.) long and weighed about 4 t (4.4 tn.).
The second species, H. stebingeri, was described in the mid 1990s from remains that include adult skeletons, as well as those of hatchlings with associated fossilized eggs and nests.
Hypacrosaurus dinosaurs are a kind of hadrosaur. The group name "hadrosaur" reflects the duck-bill shape of the members' snouts. Many different kinds of these duck-billed dinosaurs are known. Some hadrosaurs had crests on top of their heads. The crests were of many different shapes; some were solid, but most of them were hollow.
The crest of Hypacrosaurus altispinus was hollow. Scientists are not sure what purpose the hollow crest served. Interpretations suggest that the crests were used as acoustic resonating chambers for making noise used in communication or for visual display, allowing for individuals to recognize sex or species.
Hadrosaurs had grinding, elephant-like dentitions (teeth), and they seem to have appeared at the same time as woody, flowering plants. Hadrosaurs lived during the Late Cretaceous Period (from 95 to 65 million years ago).
Hadrosaurs were the most numerous plant-eating dinosaurs in the northern hemisphere during the latter part of the age of non-avian dinosaurs. Dinosaurs lived between 210 and 65 million years ago. Hypacrosaurus lived between 75 and 70 million years ago. Its remains have been found in Alberta and Montana.