Dinosaurs under the big sky

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Panel: Western Interior Seaway was a shallow inland sea that split North America in two during the middle to Late Cretaceous. Coinciding with the rise in global sea levels during the Early Cretaceous, two great arms of water—one from the north and one from the south—flooded the central low-lying interior of North America. By the start of the Late Cretaceous, approximately 100 million years ago, these two arms linked to form the Western Interior Seaway. To the west, the seaway was flanked by the rising Rocky Mountains, while relatively low and flat areas existed along its eastern shore.

The existence of the Western Interior Seaway is recorded in the rocks. Within the seaway, blankets of sand and silt were laid down along the shorelines and in shallow water settings, eventually becoming rock formations such as the Eagle Sandstone, which now form the cliffs above Billings, Montana. Deeper portions of the sea were carpeted in mud, found today in formations such as the Thermopolis Shale and Belle Fourche Shale.

The Western Interior Seaway was a defining feature of the middle and Late Cretaceous in Montana. It was inhabited by abundant marine life including aquatic birds. Periodically, volcanic eruptions in the Rocky Mountains dumped loads of ash into the sea, found today as beds of bentonite clay. As time moved on, sea levels continued to fluctuate, repeatedly flooding and then exposing low-lying areas along the shoreline. In Montana this resulted in an alternating record of marine and terrestrial rocks, some of which have been exposed

to reveal fossils like those seen in the display below the marine mural.


Paleoecology is the study of the relationships between ancient organisms and their environment. Scientists study fossils, and then use their findings to reconstruct ancient ecosystems and develop hypotheses about how ancient animals may have lived and interacted.
The Western Interior Seaway played host to a diverse array of marine life. Like modern seas, the food chain was based on an abundance of microscopic phytoplankton and zooplankton. The sea teemed with invertebrates (animals without backbones) such as ammonites, belemnites, and bivalves. Vertebrates (animals with backbones) like bony fish and a variety of sharks and rays were also common. The largest animals to inhabit the seaway were meat-eating marine reptiles.
Long before whales evolved, dolphin-like ichthyosaurs plied these waters, but became extinct during the early stages of the seaway. Montana rocks also record the presence of marine turtles, long- and short-necked plesiosaurs, and, less commonly, marine crocodilians. Beginning around 90 mya, a new group of marine lizards known as mosasaurs also made its debut.

Panel: PLESIOSAURS: The fossil specimen on the right is a plesiosaur, Edgarosaurus muddi (MOR 751B), collected in 1993 in Carbon County, Montana. The specimen on the left is the “Billings Plesiosaur”, Polycotylidae indet (MOR 955B), collected in 1991 in Yellowstone County, Montana. The model on the wall is an Edgarosaurus.
Plesiosaurs (PLEE-zee-o-sohrs) are a group of meat-eating, air-breathing marine reptiles whose fossil record is well recorded in the Cretaceous rocks of Montana. Unlike most

marine reptiles, plesiosaurs did not use their tails to move through the water. Instead, they relied on two sets of powerful paddles used for both propulsion and steering.

Plesiosaurs also exhibit a unique body plan. Some forms, such as Edgarosaurus and the “Billings Plesiosaur,” possess a short neck (fewer than 30 neck vertebrae) and a relatively large skull. In contrast, long-necked plesiosaurs, such as Eslasmosauridae, had as many as 65 or more neck vertebrae and a relatively small skull. Plesiosaurs became extinct at the end of the Cretaceous, around the same time as dinosaurs. Note: An Eslasmosauridae specimen (MOR 2577) can be seen in the Bearpaw display in the Hallway of Growth and Behavior.

Panel: MARINE CROCODILE: The specimen just above the plesiosaur fossils is a marine crocodile, Terminonaris robusta, discovered and collected by Catherine Lash, a MSU student, on private land in Carbon County near the Montana/Wyoming border. The Terminonaris was a long-snouted marine crocodile closely related to Sarcosuchus, otherwise known as “Super Croc.” Terminonaris and Super Croc were fish eaters (piscivores). Terminonaris lived in the Inland Cretaceous Seaway that existed in Montana 93 million years ago. This specimen of Terminonaris is small and probably a large juvenile or a small subadult individual. Full grown individuals may have reached 20 feet in length.
Panel Images: Images show discoverer Catherine Lash and her field crew at work on the rare crocodilian, Terminonaris robusta.


The Mesozoic Media Center contains an array of plasma screens and interactive computer displays to enhance the museum’s educational outreach programming and to provide visitors with unprecedented access to the museum’s paleontology video library and other resources.

Three large plasma screens can display videos as well as web-cam and other off-site broadcasts.


Touch screens within the center provide visitor access to the museum’s paleo imagery archives, video library, and resource files. Three vertical screens are devoted to the Paleo Video Library which provide access to one to four minute films on paleo research projects, labs, collections, theory, field sites, extraction, etc. Three screens are available to access Paleo Resources including Paleo News and Paleo Treasures. Visitors can also play interactive Paleo Games such as “Build a Dinosaur,” a game with three levels of difficulty.

Histology Hallway: Four sets of screens, placed in the corridor linking the Hall of Giants and the Hallway of Growth and Behavior, showcase high-resolution histology images taken by the museum’s Paleohistology Laboratory. Bone histology is the study of the microscopic interior structure of bone. Histology images, called photomicrographs, are produced through paleohistology microscopy. Special lenses and polarized light give color to different bone densities. The “wallpaper” along the corridor shows enlarged histology images – giving visitors an appreciation for a form of scientific art!



The Hallway of Growth and Behavior connects the Mesozoic Media Center to the Hall of Horns and Teeth. This hallway contains display cases along both walls and two large island cases in the center of the hallway. The hallway is designed to allow displays to be changed as new research and discoveries are made. Current displays include descriptive panels and Late Cretaceous fossils which showcase dinosaur eggs, embryos, growth, skulls, feet, teeth, sounds, predators, and bonebeds as well as fossils representing the Two Medicine Formation and the Judith River Formation. The two island cases feature nests of dinosaur eggs and a significant collection of dinosaur skulls. Note: As you enter the hallway from the Mesozoic Media Center, the display cases along the north (N) wall/right side are numbered N1 through N7. The cases along the south (S) wall/left side are numbered S1 through S7.


The Hallway of Growth and Behavior covers the Late Cretaceous time in Montana (85 - 70 mya). The displays showcase some of the most famous dinosaur fossil discoveries in Montana. These discoveries revolutionized theories on dinosaur growth and behavior. During the Late Cretaceous time, the interior sea level was at its lowest point creating a large coastal plain. The western shoreline was somewhere near the Montana-North Dakota border. Fossil evidence shows that dinosaurs nested and reared their young in the uplands near the Rocky Mountains during this time (DBS, p. 70-71).

In 1977, one of the world’s largest concentrations of dinosaur bones was discovered near Choteau in Teton County, Montana. The bonebed covers an area about one-half square mile and contains thousands of bones representing between 10,000 and 15,000 animals. The dominant dinosaur in this bonebed was a new hadrosaur species which was named Maiasaura. Taphonomic and geochemical studies of the site indicate that all the animals died together in a catastrophic event (e.g. covered by volcanic ash) about 75 million years ago. These studies provided evidence for the hypothesis that these dinosaurs lived in a gigantic “herd” prior to their deaths.
In these areas, Jack Horner and his team found the first clutches of dinosaur eggs from the Western Hemisphere and the first dinosaur embryos ever found in the world. They found clutches and embryos of both Maiasaura and Troodon, a small predator related to the Velociraptor. Babies were found within a Maiasaura nest and looked like they had been there for some time after they hatched. Undeveloped leg joints and trampled eggshells also indicated nestbound young not yet capable of leaving the nest. This fossil evidence led to the hypothesis that these dinosaurs cared for their young. Because of this evidence of parental behavior, the new dinosaur species was named Maiasaura, meaning “good mother reptile.”
Another nesting ground site, called Egg Mountain, was discovered in 1979 less than a mile from the upland Maiasaura nesting ground. Hundreds of dinosaur eggs and numerous skeletons of dinosaurs, lizards, and mammals have been excavated from the site. Additional research has indicated Troodon brooded its eggs, and some Troodon nesting colonies existed on islands in shallow alkaline lakes. Egg Mountain has been age dated at 76.7 million years

(DBS, pp. 19, 33, 56, 82).

The eggs, babies, and bonebed discoveries revolutionized thinking about dinosaurs that included new theories about their social behavior, migration, nesting grounds, and parental care. NOTE: The Maiasaura-related paintings used in the display cases are from the illustrations by Doug Henderson included in Maia: A Dinosaur Grows Up, by Jack Horner and James Gorman.

The museum has placed two of its most scientifically valuable specimens on display in the island display case of skulls. The skulls of Achelousaurus horneri and Hypacrosaurus stebingeri are holotype specimens which are rarely placed on display. When scientists first name extinct animals, the original specimen that is described is designated the holotype, or type specimen. Because the holotype specimen serves as the basis for naming and describing a new species, it is sometimes referred to as the “name bearing” specimen. Researchers consult the holotype specimen and its description when attempting to identify another similar fossil. It is very important that the holotype specimen remain in a museum collection with public access because researchers are continually studying these specimens (DBS, p. 83).

LATE CRETACEOUS (80 – 74 mya): During the Late Cretaceous, sea levels continued to drop and the Cretaceous Seaway receded east. The area was semiarid with extensive fern plains. Deciduous trees lined the waterways and forests of conifers grew between the waterways. Because deciduous plants grow for a period and then go dormant, animals can feed in different areas at different times of the year. Herds of duckbill and horned dinosaurs migrated across the plains. The Two Medicine Formation, along the east front of the Rocky Mountains in Montana, represents the upland area of the original coastal plain. Farther east, the Judith River Formation represents the lowland area of the coastal plain. The marine Bearpaw Formation overlies the Judith River Formation and much of the Two Medicine Formation. Abundant marine organisms have been found in the Bearpaw Formation including clams, cephalopods, snails, crustaceans, various fishes, mosasaurs and plesiosaurs (DBS, pp. 70-76). An amazing array of dinosaur specimens from the Late Cretaceous has been found in Montana including Maiasaura, Troodon, Daspletosaurus, Hypacrosaurus, Brachylophosaurus, Saurornitholestes, and Stegoceras.
Map Panel: The World and North America during the Late Cretaceous,

75 million years ago.




The Late Cretaceous Two Medicine Formation was deposited near the young Rocky Mountains between about 82 to 73 million years ago. The area was an upland where small streams and lakes were common. Most of the trees were conifers, and there were gigantic herds of dinosaurs that fed on the conifers and other plants in this area. This was also the area where numerous kinds of dinosaurs nested.
The fossils in this case represent animals that lived at various times throughout the

9 million years depositional history of the formation. The Two Medicine Formation has yielded a wide variety of dinosaur specimens including Maiasaura, Troodon, Einiosaurus, Daspletosaurus, Albertosaurus, Orodromeus, tyrannosaurid, pachycephalosaurid, Hypacrosaurus, protoceratopsian, Saurornitholestes, Stegoceras, ceratopsid, and birds. Note: This formation in northwestern Montana ranks among the world’s most productive dinosaur-bearing formations. It is probably best known for its remarkable preservation of dinosaur eggs, nests, and nesting grounds.

The panel includes a map showing the northwestern United States during the Maastrichtian (70 million years ago). The light green area in Montana represents the upland area where the Two Medicine Formation was deposited.

Case Fossil Contents: Daspletosaurus caudal (tail) vertebra and tooth

Troodon vertebra

Champsosaurus vertebra

Dromaeosaur manus (hand) claw

Palaeoscincus tooth and armor plate

Hypacrosaurus juvenile ilium (pelvic bone),

ischium (pelvic bone) and jaw

Turtle shell section (rib)

Crocodile armor plate

Euoplocephalus fused tail vertebrae and partial tail club

The Judith River Formation was deposited from about 80 to about 74 million years ago. It was deposited in a lowland area located near an inland sea that divided North America into two sub-continents. Large meandering rivers snaked their way across the lowland. Along the riverbanks were various hardwoods and conifers, palms and ferns. The climate was subtropical. The rivers were home to crocodiles, amphibians, turtles, fishes, and aquatic lizards. Dinosaurs, birds, lizards, and primitive mammals inhabited the land. Near the inland sea lived a gigantic crocodile known as Deinosuchus. In the inland sea were various kinds of marine lizards like mosasaurs, plesiosaurs, and giant sea turtles. The specimens in this case represent some of the fossils that can be found in the Judith River Formation here in Montana. The Judith River Formation has yielded Albertosaurus, Troodon, ankylosaurid, Stegoceras, tyrannosaurid, Brachylophosaurus, protoceratopsian, Avaceratops, and Ceratops.

Image on Panel: Map of the northwestern United States as it looked 75 million years ago. Eastern Montana was covered by a shallow ocean. Dark green represents the lowland area where the Judith River Formation was deposited.
Painting: A river winds across the lowland 75 million years ago. Volcanoes smoke off to the west near the young Rocky Mountains.
Case Fossil Contents: Albertosaurus maxilla (upper jaw) and teeth

Hadrosaur (duck-bill) humerus (upper arm bone), maxilla

(upper jaw), jaw fragment, and ossified tendon

Ceratopsian tooth

Theropod phalanges (toe bone), metatarsal (foot bone)

Ornithomimus phalange (toe bone)

Ankylosaur caudal (tail) vertebra; Euoplocephalus armor plate

Turtle shell fragment; Fossil wood; Fish vertebra

Lepisosteus (gar fish) scale; Gar fish skull plate


Maiasaura (MY-uh-sore-a): The Maiasaura (“good mother reptile”) is the state fossil of Montana and has not yet been found anywhere outside the state. It is known only from the Two Medicine Formation, although it is closely related to Brachylophosaurus from the Judith River Formation. Maiasaura was a medium-size, bipedal, plant-eating hadrosaur (duck-bill dinosaur) which was about 26 feet long (DBS, p. 102).
Brachylophosaurus (brach-ee-LOW-foh-sore-us): The Brachylophosaurus (“short-crested lizard”) is the most common hadrosaur found in the lower strata of the Judith River Formation. An average adult was about 23 feet long and weighed 2 to 3 tons (DBS, p. 120).
Hypacrosaurus (hi-PACK-roe-sore-us): The Hypacrosaurus (“high-ridged lizard”) was a lambeosaur (crested duck-bill dinosaur) that lived in western Montana when the inland seaway was less than 100 miles from the Rocky Mountains. A large duck-bill dinosaur, the
Hypacrosaurus could reach 30 feet in length. Like all other crested hadrosaurs, Hypacrosaurus had an expanded nasal crest on its head that it may have used as a resonating chamber for communication (DBS, pp. 104-105).

Troodon (TROH-uh-don): The Troodon (“wounding tooth”) was a small, bipedal, meat-eating dinosaur about 6 to 7 feet long and weighing about 100 pounds. Troodon was a swift predator, equipped with large grasping claws, a sickle-shaped toe claw, and sharp, serrated teeth (DBS, p. 113).
Saurornitholestes (sore-or-nith-o-LEST-ees): The Saurornitholestes (“lizard bird robber”) is closely related to Deinonychus, Velociraptor, and birds. It was a small, fierce, and fast dinosaur that was only about 5 feet long and weighed about 30 pounds (DBS, p. 114).
Daspletosaurus (das-PLEET-o-sore-us): The Daspletosaurus (“frightful lizard”) is probably the most common tyrannosaur in the Two Medicine Formation and may have been a direct ancestor of Tyrannosaurus rex. A large carnivor, the Daspletosaurus was 25 to 30 feet long (DBS, p. 111).
Stegoceras (steg-AH-sir-us): The Stegoceras (“covered horn”) is a pachycephalosaur or dome-headed dinosaur. These dinosaurs were small, gracile (lightly built), bipedal plant-eaters that were about 6 to 7 feet long. Not much is known about Stegoceras from the Two Medicine Formation because only three specimens have been found, and one of them is a juvenile (DBS, p. 106-107).


(Display Cases N1 to N5 and Island Display Cases)
Display cases focusing on dinosaur growth feature fossils and research on dinosaur reproduction, eggs and nests, embryos, babies, Maiasaura growth, and skull growth changes.


The Structure of Eggs: Dinosaur eggs were hard-shelled like those of birds. And, like all eggs, dinosaur eggs contained tiny holes for the interchange of gases. As the embryo breathed, it would take in oxygen and expel carbon dioxide. The number and size of pores in eggs may indicate whether an egg was brooded by an adult or covered with vegetation. Crocodilians (crocodiles and alligators) often cover their eggs with plant debris that heats the eggs during fermentation (rotting of the plants). Some dinosaurs, such as the hadrosaurs, may also have incubated their eggs using fermentation, while others, such as the theropods, might have used direct body contact.
Dinosaur eggs have a variety of surface structures – some are very smooth while others are bumpy. Scientists do not know the reason for these different textures, but some have suggested that they might have to do with aiding in gas exchange when the eggs are buried in debris. Research about the structure of dinosaur eggs is ongoing.
Egg Size and Shape: Dinosaur eggs come in a variety of sizes and shapes. The largest eggs known are the lambeosaurine eggs in the island display case of nests. These eggs would have been about the size of a soccer ball. They belonged to a crested duck-bill dinosaur. Another kind of duck-bill called Maiasaura laid much smaller eggs.
The lambeosaurine eggs appear to have been spherical in shape, and the Maiasaura eggs have an ovoid shape and are similar to an ostrich egg in shape and size. The eggs of Troodon and the unknown species were oblong, very similar to modern birds. Troodon eggs are found “standing” on their pointed ends in the sediment, and the unknown species eggs are found in paired rows.
Images on Panel: Troodon brooding eggs; enlarged surface of Maiasaura eggshell, Troodon eggshell, and egg from an unknown species.
Case Fossil Contents: Troodon egg; Egg of unknown taxa;

Maiasaura eggshell; Maiasaura egg replica in bronze

Hypacrosaurus eggs showing their spherical shape

Sculpture of a Troodon adult brooding its eggs

DINOSAUR NESTS ( Island Display Case)

Excavation teams from the Museum of the Rockies collected the first clutches of dinosaur eggs in the Western Hemisphere. Research shows different dinosaur species displayed different nesting behaviors and constructed different types of nests. Nest structures such as rim boundaries have been found in Montana but they are extremely rare. The little, meat-eater Troodon created a sediment rim around its egg clutch that was about 5 to 6 inches high. The duck-bill Maiasaura dug a nearly 6 to 7 foot diameter pit in a mound of dirt. Some dinosaurs appear to have simply scraped away a little dirt, laid their eggs, and then covered the eggs with sediment (DBS, pp. 41-43).

Case Fossil Contents: Lambeosaurine Egg Clutch, 1993, Hill County MT

Maiasaura peeblesorum Egg Clutch, 1983, Teton County MT

Unidentified Theropod Dinosaur Egg Clutch, 1983,

Teton County MT

Troodon formosus Egg Clutch, 1984, Teton County MT

Dinosaur embryos are extremely rare. Of the nearly 900 species of dinosaurs known, less than ten species are represented by their embryos. At the Museum of the Rockies, we have the embryos of five different species. These include the duckbills Maiasaura, Hypacrosaurus and an unnamed lambeosaur, and the meat-eaters Troodon and a dromaeosaurid. We also have an embryo of a species of fossilized turtle. Studies of embryos help us to understand dinosaur reproduction, behavior, and growth.

Image on Panel: Troodon egg with embryo. This egg was dismantled in an effort to confirm its identity.
Case Fossil Contents: Partial embryo of an unknown species of lambeosaur

(crested duck-bill); embryo of unidentified dromaeosaurid (little meat-eater);

embryonic remains of Troodon in two eggs; embryonic remains of Maiasaura;

tibia (shin bone) of an unknown species of lambeosaur.

Reconstructed cast of an embryonic Maiasaura emerging from its egg.

BABY DINOSAURS (Display Case N3)

Baby duck-billed dinosaurs, like Maiasaura, were apparently cared for and fed by their parents. Scientists think this because of the tiny size of the babies compared to adults and because the leg bones of these tiny nestlings were not strong enough for walking or running. Examination of the leg bones shows that the ends of the bones were made of fragile cartilage, rather than tough bone. We see the same kind of fragile cartilage at the ends of baby birds that are nest-bound and fed by their parents.

Painting: Maiasaura parent looking in on babies
Images on Panel: The fragile cartilage of a baby Maiasaura.

The fragile cartilage of a baby ostrich.

Baby birds waiting to be fed by parent.
Case Contents: Cast of Maiasaura adult skull

Cast of hatchling Maiasaura

Cast of nestling Maiasaura
Note: Maiasaura was cared for from the time it hatched, at least until it reached the size of the nestling (Compare size with hatchling Maiasaura to the right ). Parental attention beyond this growth stage is unknown.

One of the most interesting features about dinosaurs is that when they hatched out of their eggs, they were very small compared to their parents. For example, when a Maiasaura baby hatched, it was only 16 inches long and weighed about one-and-a-half pounds. The parent was about 30 feet long and weighed 4,000 pounds. Based on the internal structure of their bones, it is apparent that Maiasaura grew very fast. A one-year-old Maiasaura was about 9 feet in length. The panel shows a Maiasaura silhouette in six stages of growth from embryo to adult. The panel also includes a chart showing that Maiasaura’s growth pattern was more like that of a bird (emu) than a reptile (alligator).

Case Fossil Contents: Seven Maiasaura femurs ranging in size from an embryonic

femur to an adult femur.


How Dinosaur Skulls Changed as They Grew Up

The skulls of all dinosaurs changed shape as the animals grew older. Some of the different appearances may have been so that other individuals of the same species could recognize juveniles from adults. The retaining of juvenile characteristics with age is called “neoteny.” The popular term for neoteny is “cute.” Animals that are neotenous have rounded heads, big eyes, and shortened snouts. Some scientists think that young animals retain neoteny so that their parents will continue to care for them. Once they lose their juvenile characteristics, they lose parental care. Duckbilled dinosaurs retained juvenile characters until they were more than half grown. Some paleontologists think that modifications in skull shape might be due to animals changing diets as they grew up.

Discovery Opportunity: Compare the skull of the juvenile meat-eater Daspletosaurus to the adult skull in the island display case of skulls. Also compare the baby skull of the plant-eater Hypacrosaurus to the adult skull in the skull case. The juvenile Daspletosaurus had a long narrow skull compared to the adult. The baby Hypacrosaurus, however, had a very shortened skull compared to the adult. Some baby animals with shortened skulls, like puppies, are cared for by their parents. The long-snouted skulls, like that of the juvenile Daspletosaurus, might suggest that they were not cared for as long as the plant-eaters.
Painting on Panel: A Maiasaura baby hatches from its egg.
Case Fossil Contents: Juvenile skull of Daspletosaurus (cast)

Baby skull of Hypacrosaurus

Achelousaurus horneri subadult skull
Note: The Achelousaurus subadult has an ordinary nasal horn and only a small protruding spike on its shield.

DINOSAUR SKULLS (Island Display Case)
This case contains adult skulls for four different dinosaur species. Two of the skulls are holotype specimens. A holotype specimen is the individual specimen that serves as the basis for naming and describing a new species and becomes the “name bearing” specimen for that new species. In this case, the Achelousaurus horneri and Hypacrosaurus stebingeri skulls are the “name bearing” fossil specimens for two new dinosaur species.

Achelousaurus horneri holotype: Adult Achelousaurus skull. Compare with subadult skull in case N5. Young Achelousaurus had ordinary looking nose horns and lacked spikes on the backs of their shields. Achelousaurus is known only in Montana. NOTE: The Achelousaurus skull is temporarily off exhibit as of 8/29/2017.
Daspletosaurus sp. (undescribed species): Adult Daspletosaurus skull. Compare with the juvenile skull in case N5. The juvenile has larger eye openings. Compare these Daspletosaurus skulls with the Tyrannosaurus skulls in the Hall of Horns and Teeth.
Hypacrosaurus stebingeri holotype: Adult Hypacrosaurus skull. Compare with the baby skull in case N5 and the juvenile skull in case S3. Note that the baby skull lacks a nasal crest and has large eye openings. The nasal crests of these dinosaurs did not form until the animals had reached adult size. The nasal crest on its head may have been used as a resonating chamber for communication.
Brachylophosaurus canadensis: Adult Brachylophosaurus skull. Brachylophosaurus juveniles have very short nasal crests on the top of their heads and large eyes.


(Display Cases S1 to S5, S7 and N7)

Display cases focusing on dinosaur behavior feature fossils and research on dinosaur three-toed walking, sounds, and teeth and feeding. Displays also highlight dome-headed dinosaurs, dinosaur predators, and what we can learn from bonebeds.


Bonebeds are sites that produce large numbers of skeletal elements. Sometimes the elements belong to one species and other times they belong to many species. The JDM bonebed in Phillips County, Montana, contains the remains of at least five skeletons of the duck-billed dinosaur Brachylophosaurus canadensis. Bones of both juvenile and adult individuals were found in the bonebed, and the preservation supported the idea that all these individuals had lived and died at the same time. How they died is unknown, but if you look carefully at the jawbone you will see two gashes made by a tyrannosaur bite. When the jawbone was bitten, the duck-bill was already dead, so the tyrannosaur may have been scavenging.

By careful examination of the bones we can learn what happened to the skeletons after the animals died. The surface texture of many bones shows desiccation cracking, indicating that the bones laid out in the sun before being covered by sand. Some bones are crushed while others aren’t, which suggests that some may have been trampled by other dinosaurs walking in the area. The skin impression indicates that some dried out pieces of hide were lying on the surface with the bones. The sequoia branch and cone give clues as to the nearby plants.
The evidences of this bonebed suggests that these dinosaurs might have been part of a herd that perished during a drought or other disaster.

Painting: A herd of duck-bills

Images on Panel: JDM Quarry, 1998, and partial map of the JDM Bonebed.
Case Fossil Contents: Pine cone, sequoia branches, chunk of bark

Dentary tooth, skin impression, tail vertebra

Crushed pes (hind foot) phalange (toe bone) and

well-preserved pes phalange

Juvenile fibula showing desiccation cracking

Dentary (jaw bone) showing tyrannosaur bite marks

Partial skull (upside-down) showing detailed preservation


On the left is the foot of the tyrannosaur Daspletosaurus, and on the right is the foot of the duck-bill Brachylophosaurus. Daspletosaurus has long, slender metatarsals (foot bones) and phalanges (toe bones), whereas Brachylophosaurus has short, wide metatarsals and phalanges. The feet of Daspletosaurus are similar to the feet of more primitive bipedal dinosaurs, including primitive plant-eaters. Scientists do not know why duck-billed dinosaurs evolved short, flattened feet. (Note: These two fossil feet are also good examples of different-colored fossils.)

Discovery Opportunity: Compare the foot of Daspletosaurus with the foot of Tyrannosaurus rex in the Hall of Horns and Teeth. Daspletosaurus was an ancestor of Tyrannosaurus rex. Both feet are 3-toed with long metatarsals and phalanges and toe claws. The middle metatarsal is the longest. The Daspletosaurus was smaller than a Tyrannosaurus rex and so were its feet.

Daspletosaurus is found in the Two Medicine Formation (74 million years ago), and Brachylophosaurus is found in the Judith River Formation (78 million years ago).
Case Fossil Contents: Left hind foot of Daspletosaurus

Right hind foot of Brachylophosaurus


Dinosaurs are hypothesized to have made sounds because their closest living relatives, the alligators, crocodiles, and birds, all make sounds. David Weishampel at Johns Hopkins University has hypothesized that crested duck-bills used their hollow crests as resonating chambers. To test this hypothesis, engineering students here at MSU used CAT (Computed Axial Tomography) scan data to produce a rapid prototype model of the air chamber of this juvenile Hypacrosaurus. Then, they blew air through the model to determine the pitch of the potential sound.

Discovery Opportunity: Compare the juvenile skull with the adult Hypacrosaurus skull in the island display case of skulls. As you can see, the crest of the juvenile is quite small, whereas the crest of the adult is expanded and very large. In life, the juvenile made high pitched sounds, while the adult made very deep sounds called infra-sounds. Elephants produce infra-sounds. Infra-sound travels long distances. Note: The research on dinosaur sounds here at MSU was used in the movie Jurassic Park III. Jurassic Park paleontologist Alan Grant blew air through a rapid prototype model to communicate with the raptors.

Images on Panel: CAT scan image showing position of air passage way in a juvenile

Hypacrosaurus. CAT scan image of air passageway, front view.

Case Contents: Rapid prototype model of the air chamber of the juvenile


Skull of a juvenile Hypacrosaurus

Mold of the rapid prototype model of the juvenile Hypacrosaurus.

Air was passed through this mold to determine the sound pitch

of the juvenile Hypacrosaurus.

AVACERATOPS (Display Case S4)
Partial skull of Avaceratops lammersi (MOR 692)
Avaceratops is a horned dinosaur known only from Montana. The skulls of dinosaurs changed shape throughout growth. This caused juveniles and adults to look very different. The holotype (first specimen) of Avaceratops is a juvenile. Without a growth series, it is unclear if MOR 692 represents the adult form of Avaceratops or a different dinosaur.


Duck-billed dinosaurs, also known as hadrosaurs, are probably the best understood of all the dinosaurs because of the abundance of skeletons that have been collected. They are one of the most common kinds of dinosaurs. But, as common as they are, they are also very mysterious, as they are the only group of dinosaurs that appear to have chewed their food. Scientists are very sure that these dinosaurs were plant-eaters, but specifically what kinds of plants they ate is unclear. “Duck-bills,” as their nickname suggests, have wide, duck-like beaks and large batteries of teeth. Paleontologist David Weishampel has proposed that these dinosaurs could move their jaws sideways, and the sideways motion would grind the plant food between their jaws.

Some duck-bills have been discovered with plant material preserved in the area that would have been their stomachs. The plant material has been identified as parts of the branches of conifers, but whether the duck-bills ate conifer branches on a regular basis is unknown, because conifer branches might preserve better than some other kind of food that they might have preferred to eat. Because duck-bills have wide, duck-like beaks, it is quite possible that they used them like living ducks, feeding on all kinds of food items, including water plants and land plants. Whatever plants duck-bills ate would have been pretty tough; these dinosaurs had as many as 400 teeth, and all of them were replaced on a regular basis.
Painting: An adult Maiasaura with its young feeding on the leaves of a bush.
Case Fossil Contents: Side view of two Brachylophosaurus teeth showing the

chewing surface

Front view of a row of Brachylophosaurus teeth from the

dental battery

Model showing how the jaws of a duck-bill came together

to grind food

The lower jaw of the duck-bill Brachylophosaurus showing

its dental battery

Edmontosaurus jaw (MOR 003)
Note: The Edmontosaurus jaw shows the hadrosaur dental battery as seen from the inside of the mouth. Notice that each tooth row has a line-up of teeth that will come in to replace the teeth that fall out as each wears down.


Pachycephalosaurs were bipedal dinosaurs with thick, rounded skulls. Adults grew to about 15 feet long and weighed 400 pounds. For many years, scientists thought that pachycephalosaurs butted heads similar to bighorn sheep. Paleontologists proposed this behavior on the basis of the inside of the pachy’s boney skull dome. The inside of the skulls of bighorn sheep have very spongy areas to absorb the impact of butting. Studies published in 2004 by Mark Goodwin of the University of California, Berkeley, and Jack Horner (MOR) indicated that this head-butting hypothesis was wrong. It was determined to be wrong after the two researchers cut open more domes of pachycephalosaurs and discovered that the heads that were spongy inside belonged to juveniles.

Adult pachycephalosaurs had solid domes and therefore could not head-butt without causing severe damage to their skulls. At present, we do not know what these animals did with their domes, other than possibly using them for species recognition.
Fast growing bone is very spongy, like the spongy areas seen in pachycephalosaurs. The spongy nature of juvenile pachycephalosaur skulls indicates that the domes grew very fast.
Panel Images: Bighorn sheep head-butting

The spongy inside of a bighorn sheep skull

The spongy inside of a juvenile pachycephalosaur skull

Spongy juvenile dome

Solid adult dome
Case Fossil Contents: Stegoceras skull cast

Pachycephalosaurid skull dome

Stegaceras skull dome in ventral (underside) view


The top predatory dinosaurs in this region 75 million years ago were Troodon and Saurornitholestes. Saurornitholestes was only about a meter and a half long. Troodon grew to about two meters in length. Both of these dinosaurs may have hunted in groups, and both were probably able to take down large plant-eaters. Troodon remains are often found on Maiasaura nesting grounds, which suggests that they might have preyed upon nestlings.

Painting on Panel: Troodon taking a baby Maiasaura from its nest.
Case Contents: Reconstructed skeleton of Saurornitholestes

THE BEARPAW SEA (73-67 million years ago)
Throughout the Cretaceous Period, at least some part of Montana was submerged under a portion of the Intercontinental Seaway. During most of this time, the eastern shoreline existed somewhere east of present-day Billings. About 73 million years ago, the sea level rose again and inundated much of the land east of the Rockies. This insurgence is called the Bearpaw Sea, and it was inhabited by numerous sea creatures including invertebrates and marine reptiles.
InvertebrateS: The Bearpaw Sea hosted a variety of interesting invertebrate creatures. Shelled, tentacled relatives of squids and octopi—called ammonites—were among the most prolific, although giant clams, nautiloids, and even small versions of lobsters were also common. The largest of the invertebrates were gigantic ammonites called Placenticeras, some of whose shells exceeded four feet in diameter.
Case Contents: Placenticeras from Bearpaw Shale, Garfield County MT

marine reptiles: Mosasaurs and plesiosaurs were the most common of the marine reptiles to inhabit the Bearpaw Sea. The two marine reptiles exhibited here include the long-snouted, short-necked Mosasaurus, and the short-snouted, long-necked Elasmosaurus. Scientists think that plesiosaurs such as Elasmosaurus fed primarily on fish, and that mosasaurs fed on fish, ammonites, and plesiosaurs.
Note: Mosasaurus was a carnivorous swimming lizard that could reach lengths up to 30 feet. The Mosasaurus was shaped like an eel with the addition of four broad paddles used to steer. It had a huge laterally flattened tail, almost half the entire length of the animal. The head tapered to a point, and the mouth contained large sharp teeth. The Mosasaurus specimen MOR 006 was discovered in 1979 in the river breaks 60 miles south of Malta. It was found lying on its back in the soft shale of the Bearpaw Formation. Originally, this animal was over 20 feet long but only 15 feet was recovered including the skull, front paddles, and backbone.

Case Contents: Eslasmosauridae indet., collected in 2006, Fergus County MT

Mosasaurus (MOR 006), collected in 1980, Phillips County MT


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