Acristavus is a unique group of dinosaurs that lived during the Late Cretaceous period, about 79 million years ago. Its name means “non-crested grandfather.”
Acristavus belonged to a family of dinosaurs called hadrosaurs, known for their duck-like beaks. However, unlike most of its relatives, Acristavus did not have any fancy decorations on its head, like crests or horns. This makes it special because it suggests that early hadrosaurs may not have had these features, and that they developed later in evolution.
Fossils of Acristavus have been found mainly in two places: the Two Medicine Formation in Montana and the Wahweap Formation in Utah.
The first important Acristavus fossil, known as MOR 1155, was found in Montana in 1999. This fossil includes a nearly complete skull and parts of the spine and legs.
Another specimen, UMNHVP 16607, was discovered in Utah in 2000 and provides additional information about its skull and other features.
Some of the special features that help identify Acristavus include:
– A noticeable brow on the back of its head.
– A deep, square joint between its head bones.
– A specific shape of the bones around the eyes.
Acristavus belongs to a group called Brachylophosaurini, which includes other dinosaurs like Maiasaura and Brachylophosaurus.
During the time Acristavus lived, its environment was likely a wet, seasonal area with lakes and rivers. It shared its space with other dinosaurs like the lambeosaur Adelolophus and the fierce predator Diabloceratops. Other creatures living nearby included various fish, turtles, crocodiles, and early mammals.
Overall, Acristavus gives us an important glimpse into the past and helps scientists understand how hadrosaurs evolved over time.