Hypacrosaurus the Mysterious

Okay, not really mysterious. Actually, we know quite a bit about Hypacrosaurus. This comes from extensive study of Hypacrosaurus and its cousins Corythosaurus, Nipponosaurus, and Olorotitan, just to name a few; Corythosaurus and Olorotitan are its closest cousins. We know that the crest that I mentioned was barely even forming, let alone noticeable, in hatchlings did not possess an S-shaped curve like many other hadrosaurs. At about 30 feet (9.1 meters) long and 4 tonnes, it was a fairly large dinosaur with a high back profile, thanks to those tall neural spines. Its crest was helmet shaped, much like Coryhtosaurus, but has a bone spur facing backwards from the base, more like Lambeosaurus. This and many other findings have led some researchers to conclude that Lambeosaurus came first, then H. stebingeri appeared and was transitional between Lambeosaurus and H. altispinus.

©Mark Hallett

The first Hypacrosaurus found was a postcranial skeleton of H. altispinus unearthed in 1910 by Barnum Brown. Three years of preparations and study later announced a new genus to the world, still without cranial elements. Eventually these would be found as well, 5 to 10 now exist as articulated specimens (sometimes it is hard to tell if one skull is the left to another's right depending on the fossilization of course), which range in age from juvenile to adult. The other species, H. stebingeri, is known from an indeterminate number of individuals from embryo through adult, showing, as stated before, that ever important growth and maturity cycle. Speaking of which, a study was done using growth markers in bone which showed that reproductive maturity was attained within 3 years of hatching and full adult size by the end of a decade or 12 years about. This growth and early reproduction age, H. stebingeri has been found with nearly circular eggs that hold 60cm (23.6inch) long embryos, allowed for a lot of individuals of either species to exist at the same time. This in turn, helped perpetuate the species by sheer volume as the carnivores of the spans of the two species, Daspletosaurus, Albertosaurus, Troodon, Bambiraptor, Saurornitholestes, Chirostenotes, and even egg stealing mammals must have played havoc on the herds from that vulnerable egg up to the 4 tonne adult.