UPDATE - The 9th Circuit Court of Appeals on June 17, 2020 upheld the earlier court decision, affirmed by the Montana Supreme Court, that dinosaur fossils are part of the surface state, and not the mineral rights. A key factor in the decision appears to be that the value of fossils are not in their mineral content, but rather in their cultural and historical significance. This decision affirms what most property rights proponents, and the Montana State Legislature, have advocated which is that dinosaur fossils should be part of the surface rights of real property, rather than the subsurface or mineral estate.
The Montana Supreme Court on Wednesday ruled that dinosaur fossils are surface rights and not minerals according to state law. The issue arose when dinosaur fossils dubbed the "Dueling Dinosaurs" were discovered on a Montana ranch, and have turned out to be worth millions of dollars. The mineral estate owners have sued the surface estate owners claiming ownership rights to the fossils.
The case will now go back to the 9th Circuit for a re-hearing. In 2019 the Montana legislature passed a bill unanimously stating that dinosaur bones are not considered minerals, however this case predates that legislation.
The concern for property owners is that owners of sub-surface or mineral rights, which is the dominant estate in Montana, could exercise those rights and disrupt surface use and property value. This means that mineral right owners could excavate for fossils, or be entitled to the value of any fossils discovered on land in Montana. Dinosaur fossils are abundant in parts of Montana, and the designation of fossils as mineral or surface rights could have significant impact on property rights.