Hypacrosaurus

Chapter • Meet the dinosaur

Overview

Hypacrosaurus stebingeri was a large duck-billed dinosaur that reached roughly 8–9.5 metres in length and an estimated weight of 2.5–4 tonnes. It belonged to the lambeosaurines, the hadrosaurids that carried hollow head crests. The crest of Hypacrosaurus was rounded and helmet-like, lower and broader than that of its close relative Corythosaurus, and it housed looping extensions of the nasal passages. The back vertebrae bore unusually tall neural spines that gave the animal a noticeably high-backed profile, which is part of the reason for its name. The snout ended in a toothless, broad horn-covered beak, while the rear of the jaws held dental batteries of hundreds of tightly packed, continuously replaced teeth. Hypacrosaurus probably browsed on all fours most of the time but could rear up on its hind limbs to run or to reach higher vegetation. The forelimbs were robust, with a wrist and hand built to bear weight. Its diet consisted of conifer foliage, twigs, ferns, cones and low-growing flowering plants, ground down by the dental batteries in a sideways chewing motion. The hollow crest most likely worked as a resonating chamber: air pushed through the elongated nasal tubes could produce deep, carrying calls used to keep in contact in dense woodland or to warn of predators such as Daspletosaurus. The genus Hypacrosaurus was described in 1913 by Barnum Brown from material collected in Alberta (the species H. altispinus). The species stebingeri was named much later, in 1994, by Jack Horner and Philip Currie, honouring the geologist Eugene Stebinger, who reported dinosaur remains from the Two Medicine Formation of Montana in the early twentieth century. The species is above all associated with the rich egg and juvenile material from Landslide Butte in Montana and Devil's Coulee in southern Alberta, where eggshell was discovered in 1987 by amateur fossil hunter Wendy Sloboda. Thanks to those sites, H. stebingeri is one of the best-known hadrosaurids in terms of growth and development. Nests, complete eggs with embryos inside, hatchlings and individuals of every size up to full-grown adults have been recovered. In 2017 researchers used daily growth lines in embryonic teeth of Hypacrosaurus to estimate an incubation period of about 171 days, far longer than in living birds. In 2020 a research team reported preserved cartilage cells with nucleus-like structures in a skull fragment from a juvenile, a find that is still debated among scientists.

Chapter • Where it lived

Habitat

Hypacrosaurus stebingeri lived around 76–74 million years ago, during the late Campanian of the Late Cretaceous. Its fossils come from the Two Medicine Formation of Montana and the Oldman Formation of southern Alberta, Canada. The landscape was a semi-arid coastal plain east of the newly risen Rocky Mountains, with seasonal rivers, floodplains and stands of conifers, ferns and early flowering plants. The mountains lay to the west and the Western Interior Seaway to the east. Hypacrosaurus shared this world with horned dinosaurs such as Einiosaurus, armoured dinosaurs, smaller plant-eaters, and predators including Daspletosaurus and small dromaeosaurids.

Chapter • Family life

Breeding

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy