Open Paleo

Probrachylophosaurus

Freedman Fowler & Horner, 2015 pro-BRAK-ee-LOH-fo-SAWR-us

From Greek pro- (πρό, 'before' or 'ancestral to') prefixed to Brachylophosaurus, indicating a suspected ancestral relationship; meaning 'before Brachylophosaurus'

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

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.

Diagnosis

  1. Solid nasal crest consisting entirely of nasals, overhanging supratemporal fenestrae by less than 2 cm in adults
  2. Nasal crest extremely dorsoventrally thickened medially with strongly triangular frontal plane cross section
  3. Dorsal angle formed by paired nasals in posterior view less than 130 degrees (112° in adult)

Species

Probrachylophosaurus bergei Freedman Fowler & Horner, 2015

Type species

Named for Sam Berge, one of the landowners who donated the holotype fossil to the Museum of the Rockies and supported the research.

Holotype
MOR 2919 , Museum of the Rockies
Material
Majority of skull and skeleton, disarticulated. Cranial material includes premaxilla, maxillae, jugal, lacrimal, nasal, braincase, squamosals, quadrates, predentary, dentaries, surangular. Postcranial material includes cervical, dorsal, caudal vertebrae, chevrons, ribs, ilia, pubes, ischia, tibiae, fibulae, astragali, metatarsals. Forelimbs and sacral vertebrae absent.
Horizon
Judith River Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
MOR locality JR-518, Montana, United States

Notable specimens

  • MOR 1097

    Museum of the Rockies ontogeny

    A fragmentary skull of a subadult Probrachylophosaurus bergei referred to the species in the 2015 study that named the genus, found about a kilometer from the holotype. It documents a younger growth stage alongside the adult holotype.

    Freedman Fowler & Horner (2015)

References

  1. Freedman Fowler, E. A.; Horner, J. R. (2015). A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana. PLOS ONE 10(11): e0141304. Public Library of Science (PLoS). doi:10.1371/journal.pone.0141304 freedmanfowler2015a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the appearance features.

    jones2026a