Named By: Gates et al - 2011.
Classification: Chordata, Reptilia, Dinosauria, Ornithischia, Hadrosauridae.
Species: A. gagslarsoni (type).
Size: Uncertain, but probably similar to contemporary hadrosaurids of the time.
Known locations: USA, Montana- Two Medicine Formation, Utah - Wahweap Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Two almost complete skulls, possible other partial remains.
was a late surviving hadrosaurid that stood out from amongst the others
of its kind because it had no head ornamentation. Although not strictly
unique, many of the other better known hadrosaurids such as
Parasaurolophus and Lambeosaurus
had very elaborate and impressive head
crests. The fact Acristavus did not have one
suggests that it belonged
to a different group of hadrosaurids although it’s possible that it
could have been related to Maiasaura.
There are two main thoughts of reason about the lack of ornamentation. The first is that Acristavus is descended from ornamented dinosaurs, but lost the ornamentation through evolution, the result of it no longer being a desired trait in choosing a mate. Essentially this would result in it being bred out. The second is that Acristavus represents a more basal form of hadrosaurid and possible forerunner to the previously mentioned Maiasaura and possibly the more numerous Edmontosaurus.