Probrachylophosaurus

Probrachylophosaurus is a genus of hadrosaurid dinosaur that lived during the Late Cretaceous in North America. Fossils have been found in rocks of the Judith River Formation in Montana and the Foremost Formation in Alberta, and date to the Campanian age, c. 80.45–79 million years ago. The only recognized 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 were originally recognized, and in 2021 fragmentary remains would 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 genus Maiasaura.