Paleontology in Montana refers to paleontological research occurring within or conducted by people from the U.S. state of Montana. The fossil record in Montana stretches all the way out to sea where local bacteria formed stromatolites and bottom-dwelling marine life left tracks on the sediment that would later fossilize. This sea remained in place during the early Paleozoic, although withdrew during the Silurian and Early Devonian, leaving a gap in the local rock record until its return. This sea was home to creatures including brachiopods, conodonts, crinoids, fish, and trilobites. During the Carboniferous the state was home to an unusual cartilaginous fish fauna. Later in the Paleozoic the sea began to withdraw, but with a brief return during the Permian.
During the Triassic Montana was again covered in a sea whose inhabitants are the state's only known fossils from this time. Much of Montana remained covered by seawater into the Late Jurassic, but exposed areas were greened by a flora of conifers, cycads, ferns, and ginkgoes. This coastal plain was home to dinosaurs including the ornithopod Camptosaurus, the sauropods Apatosaurus and Diplodocus, and the theropod Allosaurus. During the early Cretaceous the state was home to its first flowering plants as well as predators such as Deinonychus. Later the Western Interior Seaway, home to creatures such as mosasaurs and plesiosaurs, came to cover the state. On land, the duckbilled Maiasaura formed vast nesting colonies. By the end of the Cretaceous Montana was home to some of the most famous dinosaurs; creatures such as Edmontosaurus, Triceratops, and Tyrannosaurus.
During the early Cenozoic the sea began to withdraw from the state. Plants, insects, and titanotheres are preserved from this time. Later inhabitants would include arctocyonids, insectivores, multituberculates, pantodonts, primates, and taeniodonts. As the Cenozoic proceeded the climate cooled until the Ice Age started and glaciers entered the state. At this time mammoths, musk oxen, and dire wolves lived in the areas of the state not covered by glaciers. Local Native Americans have been devising mythical explanations for fossils and also repurposing them for practical uses for thousands of years. The first scientific collection of local fossils began in the mid 19th century. Other important discoveries include the plant and insect fossils of Ruby Valley and Deinonychus, which triggered the Dinosaur Renaissance. The Cretaceous Duck-billed dinosaur Maiasaura peeblesorum is the Montana state fossil.