Taxa named by Jack Horner

Maiasaura (from , and , the feminine form of saurus, ) is a large herbivorous saurolophine hadrosaurid ("duck-billed") dinosaur genus that lived in the area currently covered by the state of Montana and the Canadian province of Alberta, in the Upper Cretaceous (mid to late Campanian), from 86.3 to 70.6 million years ago. Maiasaura is the state fossil of Montana.

Hypacrosaurus (meaning "near the highest lizard" [from Ancient Greek ὑπο- hypo- "less" and ἄκρος akros "high"], because it was almost but not quite as large as Tyrannosaurus) is an extinct genus of duckbill dinosaur similar in appearance to Corythosaurus. Like Corythosaurus, it had a tall, hollow rounded crest, although not as large and straight. It is known from the remains of two species that spanned 75.0 to 69.5 million years ago, in the Late Cretaceous of Alberta, Canada, and Montana, United States, and is the latest hollow-crested duckbill known from good remains in North America. It was

thumb|Reconstruction of the Orodromeus skeleton

Cerasinops (meaning 'cherry face') was a small ceratopsian dinosaur. It lived during the Campanian of the late Cretaceous Period. Its fossils have been found in Two Medicine Formation, in Montana. The type species of the genus Cerasinops is C. hodgskissi.

Acristavus (meaning "non-crested grandfather") is a genus of saurolophine dinosaur. Fossils have been found from the Campanian Two Medicine Formation in Montana and Wahweap Formation in Utah, United States. The type species A. gagslarsoni was named in 2011. Unlike nearly all hadrosaurids except Edmontosaurus, Acristavus lacked ornamentation on its skull. The discovery of Acristavus is paleontologically significant because it supports the position that the ancestor of all hadrosaurids did not possess cranial ornamentation, and that ornamentation was an adaptation that later arose interdependent

Trierarchuncus (meaning "captain hook," after its single-clawed hands) is a monotypic genus of alvarezsaurid theropod which includes a single species, Trierarchuncus prairiensis, mainly known from fossils found in deposits of the Hell Creek Formation in Montana. It is the youngest known alvarezsaurid and one of the last non-avian dinosaurs, going extinct during the Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago.

Platytholus is an extinct genus of pachycephalosaurid dinosaur from the Late Cretaceous (Maastrichtian) Hell Creek Formation of the United States. The genus contains a single species, P. clemensi, known from a partial skull.

Montanazhdarcho is a genus of azhdarchoid pterosaur from the Late Cretaceous period (Campanian stage) of what is now the state of Montana, United States. Montanazhdarcho is known from only one species, M. minor.

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 wo

Brontotholus () is an extinct genus of pachycephalosaurid dinosaur known from the Late Cretaceous (Campanian stage) Two Medicine and Oldman formations of Montana, United States, and Alberta, Canada, respectively. The genus contains a single species, Brontotholus harmoni, known from multiple partial domes.