Hypacrosaurus

Hypacrosaurus is a genus of herbivorous hadrosaurid dinosaurs that lived during the Late Cretaceous of western North America. It is known for a prominent cranial crest, a hallmark of many crested duck-billed dinosaurs, which likely played a role in vocalization and display.

Two species are commonly recognized: Hypacrosaurus altispinus and Hypacrosaurus stebingeri. Fossils have been found in formations in Alberta, Canada, and Montana, United States, indicating a distribution across parts of western North America during the Late Cretaceous.

Anatomy and growth: Like other hadrosaurs, Hypacrosaurus possessed a dental battery of tightly packed teeth suitable for processing tough vegetation and a beak that helped crop plants. It walked on strong hind limbs and could likely support itself on its forelimbs as well. The skull crest was formed by the nasal and surrounding bones and contained internal chambers, which may have supported vocal resonance or specialized display functions. Ontogenetic changes in crest size and shape are seen in fossil material, reflecting growth from juveniles to adults.

Paleoecology and behavior: Hypacrosaurus inhabited floodplain and marginal coastal environments with a mix of conifers, ferns, and flowering plants. As with other hadrosaurs, it likely lived in herds, which would have aided foraging and protection. Its crested head suggests social or communicative behaviors tied to species recognition or mating.

Discovery and significance: Described from North American remains in the early 20th century, Hypacrosaurus contributes to understanding the diversity and biology of crested hadrosaurs, illustrating the morphological variety within Hadrosauridae and the evolution of cranial display structures.