Step 1: Fossilization is a rare event. Organisms that die near water are most likely to be fossilized because they have the best chance of being covered by sediment carried by water.
Step 2: After death, the next essential step is for the organism’s remains to be buried by mud, clay, or other sediments (carried by water or wind), which harden around them. This encapsulates the remains, thus protecting them from scavengers, decomposition, or being carried away by currents.
Step 3: This is the step where actual fossilization occurs. In permineralization, which is common in animals, bones gradually become saturated with mineral-rich water that fills in the pores and other open spaces. The bones are not always completely replaced by minerals; sometimes some original organic material remains. The Tyrannosaurus rex known as B-rex (on display in the Hall of Horns and Teeth) yielded the first ever soft tissue discovered in a fossilized bone. In replacement, which is common in plants, the original organic material is gradually replaced in its entirety by other minerals.
Step 4: In order for the fossil to remain preserved over millions of years, it has to stay completely encased in sediment so that it doesn’t weather away from exposure.
Step 5: Through various geological processes, the earth’s crust may uplift and expose the sediment at ground level. This leads to great discoveries by paleontologists and other fossil prospectors.
Panel: HOW DO WE KNOW WHERE TO LOOK FOR DINOSAUR FOSSILS?
Geologists are scientists who study the earth’s origin, history, and structure. They make maps, called “geologic maps,” that show where different kinds of rocks are located across the earth’s surface. Paleontologists rely on these maps to know where to look for dinosaur bones.
Dinosaurs lived during a time scientists call the Mesozoic Era (230-65 million years ago), so any terrestrial Mesozoic rock could potentially yield dinosaur fossils. Tyrannosaurus rex lived 65 million years ago, so if you wanted to look for T-rex fossils you would locate 65-million-year-old sedimentary rock on a geologic map and then search the ground in that area. The exact locations of fossil remains are not predictable. To find dinosaur remains, prospectors need to walk around looking down at the ground for fossils weathering from the rock.
Be sure to always get permission to hunt for fossils! All the land in America is owned by someone. Even on public land you need permission. Note: Collecting dinosaur fossils on public lands requires a permit and collected items are stored in national repositories such as the Museum of the Rockies. Collecting on private land requires permission from the landowner, which may be an individual or a private organization.
IT IS ILLEGAL TO DIG UP OR TAKE FOSSILS FROM FEDERAL OR STATE LAND WITHOUT A PERMIT!
Panel: MONTANA IS A GREAT PLACE TO FIND DINOSAURS!
Montana is one of the best places to find dinosaur fossils because much of the exposed rock is the right age. Dinosaur remains have been found in forty-eight of the fifty-six counties in Montana. No other state has produced so many dinosaur fossils! Note: Rocks in the other eight counties are generally too young or too old to contain dinosaur fossils.
Panel: WHAT DO DINOSAUR FOSSILS LOOK LIKE WHEN YOU FIRST DISCOVER
Dinosaur remains often look like rocks, so they are usually identified by shape, color, and texture. Learning to identify fossil bones takes experience. Excavation is usually the only way to discover if an exposed bone is part of a skeleton.
Discovery Opportunity: TOUCH A FOSSIL!
Visitors can touch two fossils on display. The fossil on the left is a Triceratops horn
and the fossil on the right is a Mammoth tooth. Only one of these fossils is from a
dinosaur (Answer: Triceratops).
Discovery Opportunity: What color is a fossil?
Dinosaur fossils can be many different colors depending on the chemistry of the
sediments in which they fossilized, and how long they were exposed to sunlight
and weather. The small display case contains examples of hadrosaur bone fossils
in black, reddish, tan, dark brown, and white colors.
Panel: GEOLOGIC TIME
Geologic time is 4.5 billion years of the earth’s history that is represented by and recorded in layers of rock. Over the course of geologic time, the continents have moved and shifted, and sea levels have risen and fallen.
Dinosaurs existed for 155 million years during a time geologists call the Mesozoic Era. The Mesozoic Era is divided into three time periods called the Triassic, Jurassic, and Cretaceous. Throughout this exhibit, small map panels show the world and North America as they would have looked during the time that dinosaurs lived.
When we talk about dinosaur fossils, we often refer to the geologic formations in which they were found, as well as the time period from which they came. In geology, the word “lower” combined with a time period refers to older rock, while the word “upper” refers to younger rock. For example, Upper Jurassic rocks would be younger than Lower Jurassic rocks. In contrast, the words “early” and “late” in conjunction with a time period refer to segments of that time period, where “early” represents older dates. The Early Cretaceous was about 130-110 million years ago, and the Late Cretaceous was about 80-74 million years ago . The chart to the right illustrates how the earth changed over time, and shows the development of different plant and animal life as well.
Chart: The Eras of Life chart cross-references eras, periods, predominant
organisms, important fossil groups, and paleogeography.