User:LittleLazyLass/Ankylopollexia

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|caption=Multiview skeleton of a Hypacrosaurus

}} The type remains of Hypacrosaurus were collected in 1910 by Barnum Brown for the American Museum of Natural History. The remains, a partial postcranial skeleton consisting of several vertebrae and a partial pelvis (AMNH 5204), came from along the Red Deer River near Tolman Ferry, Alberta, Canada, from rocks of what is now known as the Horseshoe Canyon Formation (early Maastrichtian, Upper Cretaceous). Brown described these remains, in combination with other postcranial bones, in 1913 as a new genus that he considered to be like Saurolophus. No skull was known at this time, but two skulls were soon discovered and described.

During this period, the remains of small hollow-crested duckbills were described as their own genera and species. The first of these that figure into the history of Hypacrosaurus was Cheneosaurus tolmanensis, based on a skull and assorted limb bones, vertebrae, and pelvic bones from the Horseshoe Canyon Formation.{{cite journal |last=Lambe |first=Lawrence M. |author-link=Lawrence Lambe |year=1917 |title=On Cheneosaurus tolmanensis, a new genus and species of trachodont dinosaur from the Edmonton Cretaceous of Alberta |journal=The Ottawa Naturalist |volume=30 |issue=10 |pages=117–123 }} Not long after, Richard Swann Lull and Nelda Wright identified an American Museum of Natural History skeleton (AMNH 5461) from the Two Medicine Formation of Montana as a specimen of Procheneosaurus.{{cite journal |last=Matthew |first=William Diller |author-link=William Diller Matthew |year=1920 |title=Canadian dinosaurs |journal=Natural History |volume=20 |issue=5 |pages=1–162 }} These and other taxa were accepted as valid genera until the 1970s, when Peter Dodson showed that it was more likely that the "cheneosaurs" were the juveniles of other established lambeosaurines. Although he was mostly concerned with the earlier, Dinosaur Park Formation genera Corythosaurus and Lambeosaurus, he suggested that Cheneosaurus would turn out to be composed of juvenile individuals of the contemporaneous Hypacrosaurus altispinus.{{cite journal |last=Dodson |first=Peter |author-link=Peter Dodson |year=1975 |title=Taxonomic implications of relative growth in lambeosaurine dinosaurs |journal=Systematic Zoology |volume=24 |pages=37–54 |doi=10.2307/2412696 |issue=1 |jstor=2412696 }} This idea has become accepted, although not formally tested. The Two Medicine Procheneosaurus, meanwhile, was not quite like the other Procheneosaurus specimens studied by Dodson, and for good reason: it was much more like a species that would not be named until 1994, H. stebingeri.

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|caption=Proposed centrosaur evolutionary sequence

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