Dinosaurs: Inference and evidence What do we REALLY know?
How does a fossil form? 1- Death 2- Rapid burial (usually near water) 3- mineralization (water with sediments seeps through and bone parts are replaced with minerals) 4- erosion exposes fossils
Types of fossils • Fossil types include: • Cast/mold • Petrification • Trace fossils • Carbonized film • Amber
Fossils are Information…But they are incomplete information
Fossils are Evidence, but many inferences can be made from looking at fossils
So… Inferences are what gets us from the fossil evidence to the whole dinosaur.
In order to make inferences about dinosaurs, we use the law of uniformitarianism
Dinos today • Most dinosaurs went extinct, but scientists now believe that they didn’t all go extinct. • Modern day birds may have come from the dinosaurs that survived. • We can use modern day birds and crocodiles to help us make inferences about dinosaurs.
A few Dino sized questions • How did they move? • What did they eat? • Did they care for their young? • Were they warm or cold blooded?
1- How did they move? • Comparing dinosaur bones to modern day bones, we can see where muscles and tendons attached. • These reconstructions of muscles and tendons can give us a good idea about how dinosaurs were able to move.
Dino track clues • Dinosaur tracks can be used as evidence to infer how fast certain dinosaurs were able to move, but sometimes it can be difficult to tell who made the tracks.
Dino Speed • Today, we can predict how fast an animal is by comparing the size of its femur to its tibia. • Faster animals tend to have shorter femurs and longer tibias. • Femer = • Tibia =
2- What did they Eat? • Today, Carnivores tend to have sharp teeth for ripping and tearing meat. • Today, Herbivores tend to have flat teeth for grinding plant material.
Dino teeth • Along with sharp or smooth, the serrations, and curvature of teeth can help us infer what they were used for.
Dino jaw muscles • Jaw muscles can tell us a lot about what a dinosaur may have eaten. • Large area of attachment for jaw muscles indicates chewing or grinding (by herbivores)
Diet Gut size • Today, carnivores tend to have small guts because meat has a lot of easy to get nutrients • Today, herbivores tend to have large guts or multiple guts because plants are much harder to get nutrients from • Wide pelvic bones, expanded rib cages, and pelvic girdles pulled back indicate a large gut.
Did dinosaurs have cheeks? • Today, carnivores don’t tend to have much “cheek” tissue. • Today, herbivores tend to have lots of “cheek” tissue.
Gizzards or gizzard stones? • Today, some plant eaters that can’t chew their food well (like birds) have gizzards to help grind up their food. • Ancient gizzard stones (called gastroliths) have been found in some fossil dinosaurs.
Dino stomach content • Some fossils were preserved in such a way that we can infer what they ate right before they died. • We have evidence that supports dinos eating birds, dinos eating mammals, and mammals eating dinos
Dino diet - Coprolites • Fossil dinosaur poo, called coprolites, can teach us about what dinosaurs ate. • To use this evidence, you would need to infer which dinosaur made the coprolite.
3- Did Dinos care for their young? • Most birds today care for their young, but did dinosaurs?
Neoteny • Today, animals that care for their young tend to have young with neotenous (cute) features that are different from adults. • Neotenous features include big eyes, shortened snouts, retrognathia (lower jaw pulled in), etc…
Did dinosaurs care for their young? • Fossils can also provide evidence that supports parental care. Nesting Oviraptor Psittacosaurus adult with 34 young
Were dinosaurs warm-blooded? • Today, terrestrial warm-blooded organisms share some common characteristics: • Fully upright posture • Bipedallity • Long distance migration • Herd behavior • Insulation (hair or feathers) • Extreme body sizes (Blue whales and elephants are bigger than crocodiles) • Rapid growth rates
Were dinosaurs warm-blooded? • Fossil evidence can be used to infer that dinosaurs may have been warm blooded. Track evidence interpreted as 3 theropods following a herd of 12 sauropods
Modern day birds are warm-blooded (although they are cold-blooded at hatch), and some dinosaurs seem like good canidates for warm-bloodedness.
Were dinosaurs colorful? • Today, some herbivores are drab colored to blend in to their environments, and some carnivores are more brightly colored. • Today, birds tend to be brightly colored, and reptiles tend to be more drab colored.
How did dinosaurs interact? • Sometimes, interactions between species can be preserved in the fossil record.
Dino Skin Fossils • In some cases, dinosaur skin has been preserved.
How can we tell if a bone broke before or after death? • Bones that are broken while alive, or shortly after death are angular, while brittle bones that break long after death are more flat, straight, breaks This bone probably broke by being trampled on by other dinosaurs shortly after the dinosaur died. This bone probably broke long after the dinosaur had died
Fossil evidence about the world • Fossils from many things that lived before the triassic period are found all over the world, but fossils from many things that lived after the triassic period are found only on certain continents. • This evidence supports the inference that the continents were once connected. Allosaurus Fossils