Microsites are deposits where small skeletal remains from many different animals that lived in the same region have accumulated, painting a picture of an ancient ecosystem.
Microsite Geology: Microsites form in a number of different aquatic environments, as plant and animal remains accumulate in one place over time. When moving fast enough, water can transport teeth and bones. As the speed of the water decreases, the heavy objects settle out and are eventually covered by mud or sand. Such deposits are found in streams when water velocity decreases at a bend or deep pool, on floodplains when a river breaches its banks, and in lakes. Remains from fish, amphibians, reptiles, dinosaurs, birds, and mammals, as well as invertebrates (clams and snails) and plants are concentrated in the sediments. Studying the rocks and the preserved plant and animal population allows researchers a glimpse of the ecology at the time of deposition. All of the fossils displayed here are from the Latest Cretaceous Hell Creek Formation in eastern Montana (68-65 mya).
Microsite Biology: Teeth and bones from fish, amphibians, reptiles, dinosaurs, birds, and mammals are found in various abundances in Cretaceous microsites:
Dinosaurs are represented mostly by teeth, although small bones (such as toe bones) and bone fragments may also be preserved. Teeth, however, are most easily identified. Case Contents: Ankylosauridae tooth; Therapoda toe bone; Tyrannosaurid tooth; Ceratopsidae tooth; Hadrosauridae tooth.
Mammals are often uncommon in Cretaceous microsites due to low populations and small body size. Mammal teeth are the elements most often found and most easily identified. Case Contents: Meniscoessus sp. molar; Didelphodon sp. mandible.
Newts and salamanders are the most common amphibians from the Hell Creek Formation, while frog remains are less frequent. Most of these amphibians are thought to be aquatic and indicate a freshwater environment. Case Contents: Fossil parts from ancient salamanders.
Fish are often the most common fossils found in microsites. All of these fish are found in freshwater and many have close relatives found in lakes, rivers, and oceans today. Case Contents: Fossils from ancient gar, bowfin, ray, paratarpon, and sturgeon.
Turtles, lizards, and crocodiles make up the reptile component of microsites. They constitute both aquatic and terrestrial members of the ecosystem and feed on anything from plants to insects to dinosaurs. Case contents: Fossil parts from ancient crocodiles, turtles, lizards, and Champsosaurus.
The center hall exhibit case leading to the video screen displays fossil specimens of invertebrates and plants of the Hell Creek Formation.
INVERTEBRATES OF THE HELL CREEK FORMATION Mollusks (clams and snails) inhabited the sandy and muddy edges of freshwater river, streams, lakes and ponds. Filtering microscopic food particles from the water, these mollusks were an important part of the ecosystem. They were also food for many other animals, including some fish with shell-crushing teeth. The clams burrowed into the mud for safety. Clam shells seen on the surface of the ground in this exhibit represent the remains of dead individuals. Live individuals are represented in the exhibit case cut-away, showing the individuals that have burrowed into the mud.
Clams grow like trees and bones, leaving behind growth lines that can be counted to determine age. Large clams are often 100 years old. When we find accumulations of large clam shells, we know that the river system was old as well. Old river systems are good places to find the remains of rare dinosaur species because of the long, uninterrupted periods of flooding. Case Contents: Fossils of mollusks including “Gigantoclam.”
The Button Trade: Mollusks inhabited muddy river and lake edges for millions of years, long after the non-avian dinosaurs perished, and would still be common along our rivers today had it not been for buttons and pollution. The button trade nearly caused the extinction of freshwater mollusks as they were dredged from rivers and beaches. In button factories the mother-of-pearl buttons were stamped out of shells. Of some 300 species of pearl mussels native to North America freshwaters, nearly half have been lost or are in peril. About 35 species have gone extinct, most of these within the past 50 years. Case Contents: Freshwater clam shells and buttons punched from freshwater clam shells.
PLANTS OF THE HELL CREEK FORMATION Plants from the Hell Creek Formation show that the edges of rivers, streams and lakes were heavily forested with both gymnosperms (pines, ferns, and cycads) and angiosperms (flowering plants such as hardwood trees and flowering bushes). The trees were small to medium in size, and many of them had lobed leaves. The kinds of leaves that are found, including the palms, indicate that the climate was warm-temperate to sub-tropical, similar to the climates of Louisiana and Florida. There may have been fern covered plains between the rivers and streams. Grass did not exist.
Case Contents: Large fossils of petrified conifer log and palm
Smaller fossils of dicot, palm fronds, shrub, pine, fruit,
DINOSAUR REMAINS FROM THE HOPPERS FORMATION In south-central Montana 68 to 65 mya, volcanoes were spewing ash into what is now Gallatin and Park Counties. The sediments, known as the “Hoppers Formation,” are exposed in Bridger Canyon, around Livingston, and up the Shields River and occasionally yield dinosaur bones and skeletons. The bones of Tyrannosaurus, Edmontosaurus, and a protoceratopsian have been identified. Fragments of turtles and crocodiles are also known from this area.
Case Contents:Tyrannosaurus scapula (shoulder blade), humerus (upper arm
bone), and tail vertebra
Edmontosaurus tail vertebra (2), distal fibula
Therapod tooth fragment; Protoceratopsian teeth
Hadrosaur metatarsal (foot bone)
ANIMALS OF THE SAINT MARY FORMATION Living together with the little protoceratopsian dinosaur Montanaceratopswas the duck-billed dinosaur Hypacrosaurus, and a variety of aquatic animals like turtles and crocodiles. Baby dinosaurs and dinosaur egg remains are common in these sediments, suggesting that this upland area was a location for dinosaur nesting.
Case Contents:Hypacrosaurus juvenile skull, jugal (skull bone)
Hadrosaur metatarsal (foot bone)
Dinosaur eggshell; Trionychid turtle shell
Hadrosauridae tibia (shin bone)
Montanaceratops: The skeleton of Montanaceratops from the St Mary Formation 70 to 65 mya. Sixty-eight million years ago, when the horned dinosaurs Triceratops inhabited the coastal plain near the inland seaway, primitive little “horned” dinosaurs named Montanaceratops lived in the uplands near the young Rocky Mountains. These little protoceratopsians fed on plants with slicing teeth and narrow beaks similar to their giant three-horned relatives.
Case Contents:Montanaceratops skeleton (Glacier County)
FRAMED WALL DISPLAYS Two framed pieces of artwork are displayed on the wall to the right of the Montanaceratops exhibit case. The Museum of the Rockies held an art contest for children in grades K-6 to depict the Triceratops. Emily Hull, a third-grader from Belgrade, won a statewide competition that had hundreds of entries. Her artwork will be permanently displayed as part of the dinosaur exhibit. The second piece of artwork, by Jasper Wines, features dinosaurs of Montana.
Photographs of dinosaur “dig” sites are mounted along the left wall leading to the video screen:
Heading to Work, Garfield County, 2001
65 Million Years Ago On the left, Tyrannosaurus rex scavenges a dead Triceratops. A group of live Triceratops move toward the stream where a group of Edmontosaurus are drinking. The crocodile Borealosuchus waits near the stream. Sculptures by Ken Olson.
VIDEO SCREEN: BIRDS ARE LIVING DINOSAURS! As visitors head for the exit of the Hall of Horns and Teeth, they encounter a large video screen showing many different types of birds, the surviving avian dinosaurs! We are living in the Third Great Age of Dinosaurs!