Dinosaurs under the big sky

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So, what killed the dinosaurs? That’s probably the most frequently asked question from visitors to the Museum of the Rockies dinosaur halls.

THE EXTINCTION HYPOTHESIS: Controversy surrounds the cause of the demise of the non-avian dinosaurs (all dinosaurs except birds). Some people think a giant meteor struck the earth blasting dirt, rock and water into the high atmosphere. The dust and debris blocked out the rays of the sun causing darkness. The plants died, and the plant eating dinosaurs died, and soon after, the meat-eating dinosaurs also died.
There have been hundreds of explanations suggested for the cause of the dinosaur extinction including: Climate deterioration (too wet, too dry, too hot, too cold); poisons in the air, or water, or plants; heat sterilization; dwindling brains; disease; parasites; wars; anatomical disorders; old age; comets; egg-eating mammals; floods; psychotic suicidal factors; entropy; cosmic radiation; mountain building; sunspots; and little green men from Mars!

THE NON-EXTINCTION HYPOTHESIS: 64.5 million years ago, a few groups of non-avian dinosaurs became extinct at the Cretaceous-Tertiary boundary. In the panel images, you can see the dark layer of coal known as the Z-coal, the Cretaceous-Tertiary boundary. Non-avian dinosaurs are found below the Z-coal, but not above it. The group of theropod dinosaurs that did not experience extinction are the avian dinosaurs, better known as birds. Because birds survived, it is clear that dinosaurs have not yet gone extinct. As long as birds exist, theropod dinosaurs exist.


Updated as of 09/05/2015

Paleontologists use the scientific process, including physical evidence (e.g. fossils) to develop scientific theories about dinosaurs.
Different dinosaurs lived at different times in the Mesozoic Era.
Fossil evidence can tell us about dinosaur growth and behavior.
Dinosaurs are the ancestors of birds.
The science presented within the Dinosaurs under the Big Sky exhibit was accomplished by students, former students and staff of Montana State University.

How does the Science of Paleontology works? How do we know what we think we know about Dinosaurs?
- Physical evidence (fossils)
- Science- observation of physical evidence, hypothesis, attempt to falsify (not verify)
hypothesis, scientific theories
- Serendipity
How do we learn from fossils?
- Ontogeny- study of growth
- Taphonomy- study of fossil burial
- Paleohistology- study of fossil bone structure
- Comparative anatomy- similarities/differences between modern and ancient animals
- Paleotechnology- LIDAR, CAT scanning, SEM, etc
What is a dinosaur?
- Dinosaurs were a special kind of reptile that walked with their legs directly underneath

their bodies

- Avian/non-avian dinosaurs
- Reptiles
Geologic Time: Where do dinosaurs fit in?
- Dinosaurs existed for a long time (~165 million years) – different kinds of dinosaurs

lived at different times during that period

- Plate tectonics/climate changes over time
- Rocks form layers
Relatedness (evolution)
- Change occurs from one generation to the next (you are different from your parents)
- Changes add up over generations (many, many generations in geologic time)
- The mechanism for evolution is debated (Darwin)
- Organisms with more similarities are more closely related (cladistics)
- Raptor dinosaurs gave rise to avian dinosaurs (birds) during the Jurassic period. Birds

survived the extinction that killed the non-avian dinosaurs, have diversified

and still exist today.
- Rare
- Quality of preservation
- Permineralization/petrification
- Advancing Science
The Big Picture
- Ecosystems
- Biodiversity
- Recorded in fossil record


Science as Inquiry—How do we know what we think we know about dinosaurs?

  • Science is a cycle—

  • Science advances as we learn more and modify our current understandings

  • Physical evidence is the most important clue scientists can use to learn about dinosaurs

  • In the science of paleontology, the physical evidence is fossils

  • Paleontologists observe and compare fossils from extinct life to learn new information—you will see many examples of this in DuBS

  • A hypothesis is a scientific idea supported by physical evidence

  • Scientists come up with hypotheses based on what they think the fossils are telling them, then they try to find ways to test those hypotheses and prove they are wrong by using the physical evidence

  • If after exhaustive testing a hypothesis has not been proven wrong, it can be called a scientific theory

  • The Theory of Gravity is an example of a scientific theory that has not yet been proven wrong

What is a dinosaur?

  • A group of reptiles that lived 230-65 million years ago during the Mesozoic Era

  • The only reptiles to walk with their legs right under their bodies, not sprawled to the sides

  • Scientists have found many lines of evidence supporting the idea that birds evolved from dinosaurs

  • Dinosaurs that lived in the past and that are extinct are called non-avian dinosaurs and dinosaurs that live now are called avian dinosaurs, or birds

  • In DuBS, we focus on non-avian extinct dinosaurs, but we will look at evidence that supports the idea that birds are dinosaurs

  • There are many extinct animals that are not dinosaurs—wooly mammoth, saber-toothed tiger, Dimetrodon, swimming reptiles, flying reptiles

  • Humans lived long after the dinosaurs—humans and non-avian dinosaurs never lived at the same time

Different dinosaurs, different times, different places in Montana

  • The Mesozoic Era (the time when non-avian dinosaurs lived) is divided into three parts—the Triassic, Jurassic and Cretaceous periods

  • DuBS focuses on the Late Jurassic through the end of the Cretaceous period--about 90 million years of that time

  • Different dinosaurs lived in different times and places in Montana—we find their fossils in different layers of rocks, called formations

  • In DuBS, you will see what kinds of dinosaurs lived together at different times in Montana

  • Scientists also find fossil evidence of plants and other animals in each formation—this helps them piece together what each environment might have been like

How do we know where to find dinosaurs?

  • Geologists (scientists who study Earth’s processes) make maps that show where different age and types of rocks are exposed at the Earth’s surface

  • Paleontologists look on geologic maps to find areas where the right age and type of rocks are exposed

  • They get permission to “prospect” in those areas for dinosaur bones

  • In DuBS, you will visit areas that show what kinds of dinosaurs were found in different rock formations of different ages


  • The dinosaurs in this part of the exhibit come from the Late Jurassic period—about 150 million years ago

  • The fossils from these dinosaurs were found in the Morrison Formation

  • These are some of the earliest dinosaur fossils found in Montana—we don’t have fossils from the Triassic and Early Jurassic because those earlier formations have few exposed rocks in Montana

  • The main dinosaur fossils we find from this time period include sauropods (Diplodocus/Apatosaurus—previously Brontosaurus), Allosaurus and Stegosaurus

Sauropod Growth Series

What we think we know: It took about 20 years for a baby sauropod to grow to adult size.

How we know what we think we know:

  • A growth series is a series of the same bone from more than one individual dinosaur of the same type at different ages

  • Scientists learn the most about a certain type of dinosaur by finding many individual specimens of various ages—then they can see how the animal changed throughout its life

  • Sauropod growth series—comparison of hind legs from a baby (out of egg for two weeks, less than 20 lbs.), juvenile (25 feet long, 2 tons), and adult (70 feet long, 20 tons—at least three elephants)

  • Ontogeny is the development of an organism from embryo to adult

  • Scientists can study the inside of bones using histology—cutting thin sections of bones and studying them under a microscope—the bones have rings kind of like tree rings

  • By comparing histological data from different aged dinosaurs of the same type, scientists can begin to understand how old an animal could live and how fast it grew

  • It took about 20 years for the adult to grow from a baby

Mother’s Day site

What we think we know: Juvenile Diplodocus travelled in groups, some died when they got

stuck in mud and couldn’t get out, and Allosaurus fed on the dead or dying Diplodocus

How we know what we think we know:

  • Scientists can learn a lot from the arrangement of fossils in the ground—this is called taphonomy

  • Scientists make detailed maps of dig sites before and during the excavation

  • These bones may appear to be randomly arranged, but careful observation reveals lower legs and feet from juvenile Diplodocus are intact in the jumble of bones

  • The kind of rock in which these bones are found is mudstone which forms where there is slow moving or still water—like on a floodplain

  • Allosaurus teeth and Diplodocus bones with teeth marks were found here, too

  • It is important to be patient and map a dig site to get the most information

  • It is important to bring in a paleontologist to dig up fossils correctly so that we don’t lose scientific information

Warm bloodedness

What we think we know: Dinosaurs were warm blooded

How we know what we think we know:

  • Warm blooded means an animal keeps a steady, high internal temperature regardless of the outside temperature

  • Endothermy—means “inside heat”—an endotherm maintains temp. at constant level

  • Ectothermy—means “outside heat”—an ectotherm responds directly to outside temps.

  • Homeothermy—maintenance of constant body temp.

  • Heterothermy—body temperatures vary, but not to the extreme of the environment

  • Poikilothermy—wide temperature variation

  • Endotherms—high metabolism (fast cellular and chemical activity in body)

  • Ectotherms—lower resting metabolism

  • Evidence shows that dinosaurs were endothermic heterotherms—warm blooded, body temp. does vary, but not by too much—allowed them to maintain large body sizes by requiring less food

  • Histological evidence—open spaces in dinosaur bones indicate presence of many blood vessels and quick growth

  • Egg evidence—birds are endothermic and brood (sit on eggs) and scientists have found fossil evidence of some dinosaurs brooding

  • Feather evidence—feathers on birds insulate to retain heat and scientists have found fossil evidence of feathered dinosaurs

  • Heterothermy—dinosaurs gave rise to birds and birds are heterothermic so we hypothesize that dinosaurs were, too

Dinosaurs didn’t drag their tails

What we think we know: Dinosaurs didn’t drag their tails

How we know what we think we know:

  • Scientists used to compare dinosaurs to living reptiles and so thought they dragged their tails

  • John Ostrom (1970) discovered Deinonychus and Tenontosaurus with structural extensions of bones and muscle, called zygapophyses (ZIG-uh-POF-uh-sees) which prevented their tails from dragging

  • Functional anatomical studies have shown that all dinosaurs did not drag their tails

Bird/dinosaur relatedness (Display case/panel and Deinonychus mount with feathers)

What we think we know: Birds are dinosaurs, or birds evolved from Dromaeosaurid and/or

Troodontid dinosaurs

How we know what we think we know:

  • Animals with the most shared characteristics are the most closely related to one another (based on our understanding of evolution and extinction)

  • Birds share more characteristics with certain groups of dinosaurs (Dromaeosaurid and Troodontid dinosaurs) than with any other group of animals

  • Fossil evidence indicates the following shared characteristics between birds and dinosaurs (there are many more): wishbone, hollow bones, extra-long digit II of the hand, oblong hard-shelled eggs, semilunate carpal bone, three-toed foot, egg brooding

  • Birds are living dinosaurs

Raptors hunted in packs

What we think we know: Raptors, specifically Deinonychus, hunted in packs

How we know what we think we know:

  • The arrangement (taphonomy) of this fossil provides information about the dinosaurs

  • Eleven Deinonychus teeth (too many to have come from one Deinonychus) were found around one Tenonotosaurus skeleton

  • Dinosaurs, like modern reptiles, lost their teeth throughout their lives and lost them regularly while feeding

Some dinosaurs dug burrows

What we think we know: A new species of dinosaur, Oryctodromeus cubicularis, dug burrows.

How we know what we think we know:

  • Oryctodromeus fossils of an adult and two juveniles were found within a chamber at the end of a burrow nearly seven feet long

  • Dimensions of burrow fit the body size of Oryctodromeus

  • Orcyctodromeus shows shoulder, arm and hip structure similar to modern animals that dig burrows

Montana had oceans in the past

What we think we know: Montana was partially covered by shallow seas at times in the past How we know what we think we know:

  • We find sedimentary marine deposit rocks (sandstone, siltstone) that formed in shallow seas and contain fossil evidence of marine reptiles and other sea creatures

  • This transgression of the Western Interior Seaway cut North America into two pieces (East and West America) about 90-100 mya

  • Animals that lived in the seas were not called dinosaurs even though many lived at the same time dinosaurs lived on land

  • Montana’s prehistoric sea creatures include: plesiosaurs (short- and long-necked), ichthyosaurs, marine crocodiles, sharks, belemnites

Dinosaurs cared for their young

What we think we know: Maiasaura cared for its young

How we know what we think we know:

  • Scientists have found evidence of nesting grounds

  • Tiny size of babies compared to adults

  • Evidence that leg bones of nestlings not strong enough for walking or running—fragile cartilage ends of leg bones (similar to baby birds in nests)

Maiasaura Growth Series

What we think we know: Maiasaura grew quickly to adulthood

How we know what we think we know:

  • Maiasaura grew from 11-inch babies to 30-foot long adults

  • Comparison of Maiasaura fossil femurs (thigh bones) shows changes from a 2-inch baby femur to the adult’s nearly 3-foot femur.

  • Histology microscopic studies of the adult femur showed the Maiasaura rapidly grew to adult size in only seven years

Adult Pachycephalosaurus did not butt heads

What we think we know: Adult Pachycephalosaurus did not butt heads

How we know what we think we know:

  • Scientists used to think Pachycephalosaurus butted heads like modern big horn sheep due to bony skull domes

  • Big horn sheep have spongy skull domes that allow for the impact of head butting

  • Jack Horner and Mark Goodwin (Berkeley) made histological thin sections of skull domes—found adults were solid and juveniles were spongy

  • Spongy bone structure indicates quick growing bone in juveniles

  • Only juveniles could have head butted

  • Adult skull domes may have been for species recognition

Triceratops Growth Series

What we think we know: Triceratops probably used its horns for species recognition

How we know what we think we know:

  • The Triceratops growth series shows evidence that Triceratops horns changed from pointing back to pointing forward as the Triceratops reached adult size

  • Scientists used to think that Triceratops used its horns and shield for defense

  • MOR scientists find this highly unlikely due to evidence

  • Horns were hollow at the base and could have broken

  • Shield full of blood vessels and puncture would have resulted in massive blood loss

  • What were horns/shield for?

  • Attracting mates?—not likely because both males and females had them

  • Species recognition?—likely because many ceratopsians (Triceratops) had similar body plans

Tyrannosaurus rex Growth Series

What we think we know: Dinosaurs changed as they grew up

How we know what we think we know:

  • Baby animals change in appearance as they grow up

  • As T.rex grew up, the skull got larger and heavier

  • Young T.rex had larger eyes than adults

  • The younger T.rex had more teeth (60 teeth) than adults (48-50 teeth)

  • Young T.rex had small, sharp, blade-shaped teeth to cut flesh while adults had large, blunt, rounded teeth for crushing bone.

Tyrannosaurus rex was a scavenger

What we think we know: T.rex was a scavenger instead of a predator

How we know what we think we know:

  • Some scientists think T-rex was a predator

  • Jack Horner has found evidence suggesting that T-rex was a scavenger

  • T-rex was a common meat-eater in the Hell Creek Formation, nearly as common as the plant-eating, duck-billed Edmontosaurus. In any ecosystem, predators are extremely rare compared to the plant-eaters, but scavengers are common.

  • T-rex had powerful teeth and jaws that could crush bone (bite force measured at 2,900 pounds, similar to the hyena which is a scavenger)

  • T-rex bite marks have been discovered in fossils of Triceratops, Edmontosaurus, Tyrannosaurus rex, duck-bills and other dinosaurs with no evidence of healing

  • Evidence from T-rex coprolite (fossilized dung) showed T-rex had fed on a Pachycephalosaurus

  • T-rex bite marks and coprolite contents do not provide evidence that a T-rex killed an animal – only that it ate it!

  • Large olfactory lobes – good for long-distance smelling abilities, similar to turkey vultures (scavengers)

  • Small optic lobes – poor eyesight for hunting

It’s a Girl!

What we think we know: The Catherine T.rex was a female

How we know what we think we know:

  • Inside the femur of B.rex (now known as Catherine) scientists found a special layer of bone tissue

  • The bone tissue is called “medullary bone” and is only found inside the bones of female birds just prior to and during their egg laying cycles

  • Dr. Mary Schweitzer compared the T.rex medullary bone to ostrich medullary bone—it was very similar

  • Dr. Schweitzer determined that this T.rex was female and in the middle of her egg laying cycle when she died

Soft Tissue—science in progress!

What we think we know: Scientists think they have found preserved blood vessels and cells in

dinosaur bone

How we know what we think we know:

  • Dr. Mary Schweitzer used a new method of removing hard bone matrix from a fossil using acid

  • When the hard material was dissolved, soft, flexible tissue was left behind

  • The tissue very much looks like structures such as blood vessels and cells

  • Scientists didn’t know that tissue could be preserved this way

  • Mary Schweitzer is also trying to determine how this fossilization occurs

  • Her research could change our understanding of the fossilization process

  • We currently think fossilization happens through permineralization or petrification

Bird Video

What we think we know: Dinosaurs are not extinct

How we know what we think we know:

  • Extinction hypothesis vs. non-extinction hypothesis

  • We know most of the non-avian dinosaurs died out around 65 mya

  • We don’t know for sure why but there are many theories—probably a combination of several

  • It is generally accepted in science, due to the evidence that you see in DuBS and more,

that a group of therapod dinosaurs—avian dinosaurs, or birds—lived through the extinction event and live on today.




Note: The Wankel T-rex skeleton is on a 50-year loan to the Smithsonian Institution in Washington, D. C for display at the National Museum of Natural History.

Excavation of the Wankel T-rex: Big Mike, the bronze replica on the Museum’s front lawn, was cast from the bones of the Wankel T-rex. When the Wankel T-rex was taken out of the ground, it was divided into several giant, plaster-wrapped packages and lifted onto trucks with loaders. The largest of the plaster packages weighed about 8000 pounds and required a loader to get it off the ground and onto a flatbed truck. When the plaster jackets were lifted, additional plaster was added to the bottoms to ensure safe travel back to the museum.
The Wankel T-rex was discovered by Kathy Wankel of Angela, Montana, while her husband, Tom, was fishing on Fort Peck Reservoir in McCone County in 1988. On the side of a small knob that would have been an island when the lake was full, Kathy found three bones that she was not able to identify. She brought the specimens to the Museum of the Rockies where Jack Horner and staff identified them as parts of a T-rex arm. They were the first T-rex lower arm bones (ulna and radius) that had ever been found.
During the summer of 1989, a MOR crew went out to search for more bones of Kathy Wankel’s T-rex, but wasn’t able to confirm that a skeleton was preserved in the small hill. The following summer, however, a second team dug a few test pits, found the skeleton, and excavated it. When the Wankel T-rex was excavated in 1990, it was the first specimen to be found with an arm, and at the time it was the largest and the most complete T-rex specimen ever found. A slightly larger and more complete specimen, nicknamed “Sue,” would be found later. The Wankel T-rex was excavated by a team of 12 paleontologists over the course of one month. The excavation was recorded by a great many media organization, including NOVA, Time magazine, and numerous newspapers.
The Wankel T-rex died in a river. This skeleton was found in sandstone originally deposited by a river. Part of the carcass was still articulated, but the right leg, skull and end of the tail were dislodged. The right leg and skull remained close to the skeleton, but some of the tail bones, a few toe bones, the right arm and a jaw washed away. Some of the largest bones of the skeleton, the skull, and leg bones were moved to the tail end of the skeleton indicating that the animal had fallen into a swift, deep river. The neck is pulled backward which is a condition common to warm-blooded animals that are thought to have died slowly.

The bones of the Wankel T-rex do not appear to be any better preserved than those of other dinosaur skeletons from the Hell Creek Formation, but microscopic examination revealed extraordinary structures, including blood vessel canals and cell-like objects. MSU Doctoral student Mary Schweitzer (now Dr. Schweitzer at North Carolina State University) carefully examined the internal cavities of the bones which revealed that little replacement of the original bone had taken place. Biological iron (heme) and the protein collagen were successfully extracted from the femur (thigh bone). There were also structures containing the remnants of red blood cells.
How old was the Wankel T-rex when it died? Microscopic studies conducted by Jack Horner (MOR) and Kevin Padian (UC Berkeley) of the tibia (shin) revealed that the Wankel T-rex died at age 14, plus or minus two years. Dinosaur bones have growth lines just like trees. These lines represent annual changes in growth. Counting the lines that are present, and calculating for missing lines due to erosion of the marrow cavity wall, gives the age of the dinosaur. The Wankel T-rex tibia has seven lines, and another seven lines are calculated to have been present.

To discover if T-rex was a predator or a scavenger, paleontologists ask the question, “How did T-rex get its meat?” Then they look for physical evidence because science is all about physical evidence, and not about opinion.
Physical Evidence 1: T-rex ate Triceratops. MOR Research Associate Ken Olson and former graduate student Greg Erickson studied holes in the pelvis of a Triceratops and found that the holes were made by a T-rex. The absence of any healing around the holes indicates that the Triceratops was dead before the punctures were made. There is no evidence to indicate that the T-rex killed the Triceratops – only that the T-rex ate the Triceratops. The bite marks on both the upper and under sides of the pelvis indicate that the body of the Triceratops had been completely torn apart, as the pelvic bone is normally deeply embedded in muscle. Studies of the puncture marks determined that T-rex had bitten the bone with a bite force of 2,900 pounds, a force proportionately similar to the bite of a hyena.
Physical Evidence 2: T-rex had long-distance smelling abilities! T-rex had very large olfactory bulbs, which determine sense of smell. Turkey vultures have exceptionally large olfactory bulbs, but animals like the bloodhound have small olfactory bulbs, and large, sensory filled noses. Bloodhounds’ noses are for smelling tiny amounts of scent on the ground under their noses, while turkey vultures’ noses are for smelling scents over long distances in the air. Turkey vultures can smell carcasses over distances of more than 25 miles. T-rex also had very small optic lobes. The small size of these lobes suggests that T-rex had poor eyesight. (Note: The large olfactory bulbs and small optic lobes can be shown and discussed with the T-rex braincase endocast.)
Physical Evidence 3: Leg bones of T-rex and an ostrich. Studies of Tyrannosaurus rex leg bones, conducted by John Hutchinson of the University of California at Berkeley and Mariano Garcia from Stanford University, determined that T-rex couldn’t run very fast. They revealed that T-rex may not have run at all. To make this hypothesis, they compared the musculature of T-rex with that of a chicken. When the chicken was enlarged proportionally to that of the T-rex, the chicken couldn’t run either. This kind of research is called “biomechanical.” (Note: What would have happened to T-rex if it had tripped and fallen down? Paleontologist Jim Farlow of Indiana University calculated that T-rex would have likely died or have been badly injured).
Physical Evidence 4: T-rex was a common meat-eater! In the Hell Creek Formation where T-rex is found, T-rex is the most common meat-eater, nearly as common as the plant-eating, duck-billed dinosaur Edmontosaurus. The Museum of the Rockies has 12 specimens of Tyrannosaurus rex. In any ecosystem, predators are extremely rare compared to the plant-eaters, but scavengers are common.

REMOVAL OF MODEL DINOSAURS PREVIOUSLY ON DISPLAY IN THE SIEBEL DINOSAUR COMPLEX: The large Triceratops model display in the Hall of Horns and Teeth was removed to make room for the Tyrannosaurus rex display, “The Tyrant Kings.” Display panel information was incorporated into the Triceratops section of the Docent Manual. To make room for the “Burrowing Dinosaur” display, the Museum removed the “Sauropod under Attack” display model dinosaurs (sauropod and pair of Deinonychus) along with the case of claws and the panel on sexual dimorphism. Display panel information is provided below as background information. The model dinosaurs were shipped to Japan for use in dinosaur museum exhibits.

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