Probrachylophosaurus

Probrachylophosaurus is a genus of large herbivorous brachylophosaurin hadrosaurid dinosaur known from the Late Cretaceous (Campanian) Judith River Formation of Montana and the Foremost Formation of Alberta. The type (and only named) species is Probrachylophosaurus bergei. First discovered in Montana in 1981 and not fully excavated until 2008, it was initially suspected to be a new species of Brachylophosaurus. However, in 2015 it was named as a distinct genus, with its name reflecting a suspected ancestral relationship. Both an adult and subadult specimen are known, and fragmentary remains would later extend its known range into the Foremost Formation. Thought to be a close relative of the later Brachylophosaurus and Ornatops, and a possible descendant of the older Acristavus, it represents a possible transitional state in brachylophosaurin evolution. Nonetheless, whether this represents a single evolutionary lineage or a series of diverging or convergent branches remains unclear, as does its relation to the highly distinct genus Maiasaura.

As a hadrosaur, Probrachylophosaurus would have been a large herbivore, in length, that walked on four legs and possessed a large beak. Like many other hadrosaurs, it was distinguished by its head crest, likely used for display. In Probrachylophosaurus this crest is a short, paddle-shaped extension of the projecting over the back of the head. It is tallest in the middle and triangular when seen from behind. This distinguishes it from Brachylophosaurus, which had a longer crest with a flat shape formed by the nasals and the . In both genera, the frontals bear long striation marks termed the "nasofrontal sturue", expanded for the sake of supporting the large crest. In Probrachylophosaurus these cover only half of the frontal surface, unlike the later Ornatops and Brachylophosaurus where they expand further and in the latter cover the entire frontal. Aside from the crest, its skull shows an intermediate anatomy between the robust Acristavus and the more lightly built Brachylophosaurus. The only known specimen possesses several injuries, including a series of fractured tail vertebrae that may have been damaged by interactions with other hadrosaurs.