Chris McGowan
IIIkk
!
Series Learn & Try
PalaeONTOlogY idea: Ljiljana Marinkovi} author: Chris McGowan • illustration and design: Du{an Pavli} editor: Slavica Markovi} • lecteur: Violeta Babi} editor in chief: Ljiljana Marinkovi}, general manager publisher: KREATIVNI CENTAR, Gradi{tanska 8, Belgrade tel: +381 11/ 38 20 483, 38 20 464, 244 06 59 www.kreativnicentar.rs • info@kreativnicentar.rs print: Publikum Copyright©KREATIVNI CENTAR 2007
Chris McGowan
PalaeONTOlogY Illustrated by
Dušan Pavlić
CONTENTS 5 ... What is palaeontology?
20 ... The dinosaur preparation lab
6 ... What are fossils?
22 ... Mould and cast a chicken bone
7 ... Experimenting with fresh bones
23 ... Great Palaeontologists
8 ... Fossilization
26 ... (local palaeontology)
10 ... Discovering what happens to bones in nature 11 ... Faking a fossil footprint 12 ... What are dinosaurs? 14 ... When did dinosaurs live? 15 ... Make your own geological time scale
27 ... How to become a palaeontologist 27 ... The good things about palaeontology 27 ... The not so good things about palaeontology 28 ... Are dinosaurs really extinct?
16 ... Try being a bipedal (two-legged) dinosaur
28 ... Flying feathers
17 ... Collecting dinosaurs
30 ... Glossary
18 ... Unearthing and collecting your own dinosaur bone
32 ... Index
19 ... Experimenting with sediments
29 ... The future of palaeontology
... i vra}am ti ovog tvog la`nog DINOSAURUSA!
What
P
is palaeontology?
eople often get archaeology and palaeontology confused because both involve digging up old things. However, while archaeologists study ancient peoples, and the way they lived, by unearthing human remains, buildings, utensils, tools, furniture, art, and all the other objects of human civilizations, palaeontologists study extinct animals and plants. Also, the fossils palaeontologists study are often many millions of years old, whereas archaeologists’ treasures are usually aged only a few thousand years. Many geologists study fossils too—mostly small ones like shells—but their main interests are rocks, not animals and plants. Palaeontology, like any other branch of science, is partly detective work. It involves being observant, discovering new information, testing ideas with experiments, and keeping good notes. The last point is really important because it allows you, and others, to repeat your work. So get yourself a notebook and get into the habit! Scientists are inquisitive and want to learn new things. The best way to learn is through your own hands-on experience, which is why there are so many activities in this book. Scientists are also cautious, and don’t accept anything as a fact unless there is good evidence. So don’t be afraid to ask questions—it’s part of being a scientist.
1. Palaeontologists who study animals with backbones (vertebral columns)—fishes, amphibians, reptiles, birds and mammals—are called vertebrate palaeontologists.
2. Those interested in all the other animal kinds, which includes insects, snails, worms, spiders, sponges and corals, are called invertebrate palaeontologists.
3. People who study plant fossils are called palaeobotanists.
5
Suppose I put a dinosaur bone into your right hand and a similarly-sized cow bone into the other. You’d notice the dinosaur bone was much heavier, and was brown or black rather than white. It might feel cold, like stone, and if you dropped it the fossil might shatter. Looking at a broken piece could reveal a mass of crystals, glinting like glass beads.
Znao sam da ovako ne{to mora da postoji!
6
What are fossils? Fossils are the remains of animals and plants, usually hard parts like bones, teeth, shells and wood. There are also trace fossils, which are not parts of the actual plants or animals themselves. These include footprints, leaf and skin impressions, pollen grains, and even animal burrows. The word fossil comes from a Latin word meaning “dug up.� So if your dog dug up a bone in your garden, you could say he had found a fossil. However, palaeontologists use the word only for things that are thousands or millions of years old, like mammoth tusks and dinosaur bones. As this book is about vertebrate palaeontology (see box on page 5), mostly dinosaurs, our focus will be on fossil bones and skeletons. How do bones become fossils? Before we can understand this process, called fossilization, we need to know about modern bones. And the best place to start is in the kitchen.
Experimenting with fresh bones Next time you eat chicken save three of the bones. You can use the femur (thighbone), tibia (shinbone), or humerus (upper arm bone). Ask an adult to boil them for about thirty minutes. Then rinse them in cold water, removing the meat and gristle by scrubbing—an old toothbrush is good for this. There may be thick caps of cartilage (gristle) at either end of the bones. This shows that the chicken was young and still growing. Don’t worry if the cartilage comes off, you don’t need it. Leave the bones to dry overnight. How strong are bones? Can you break one in your hands? No, but you might feel it “give” a little—bone is elastic (springy), as well as stiff. Drop one onto a hard floor. It doesn’t shatter—bone is tough, not brittle like glass. Bone is made of two main substances: a mineral, called apatite, which makes it hard and stiff, and a protein, called collagen, which makes it elastic and tough. You can test this for yourself with some experiments. Put one of the bones into a small container, cover it with vinegar and leave for at least ten days. This will dissolve the apatite. Ask an adult to put a second bone into an oven, set at 150° C (300° F), for two hours—this breaks down the collagen. Leave the third bone untreated, for comparison. The first bone, now mostly collagen, feels soft and rubbery, and easily pulls apart. The second bone is still hard and stiff, but it’s brittle, and no longer tough. It’ll snap like a biscuit, shatter if dropped, and can be scratched with a fingernail. If you looked carefully at a broken piece of the bone you would see it was spongy, with masses of tiny pores or spaces.
A
B
C
A) HUMERUS
B) FEMUR
C) TIBIA
Bones are living parts of the body and some of the spaces contained blood vessels and nerves—this explains why breaking a bone is so painful. The microscopic spaces contained living bone cells, which maintain and build new bone material. Your bone cells are actively forming new bone as you continue to grow.
7
Fossilization
Scientists studying dead bodies in Africa were surprised at how quickly an animal as big as an elephant was destroyed, even without the help of large scavengers like hyaenas. Within two weeks, insects and bacteria had demolished all the elephant’s soft parts (internal organs and muscles), leaving the skeleton encased in the sun-baked skin. A year later, all that remained of the elephant were some scattered bones, many of which had been broken.
8
How many birds can you see in your neighbourhood? If you kept score, you’d probably see hundreds during a week (try counting them for ten minutes). If birds are so numerous, why do we seldom see dead ones? When animals die their bodies are quickly broken down and destroyed by scavengers. Local cats, dogs and foxes do most of the scavenging where you live. Anything left behind gets eaten by invertebrates, especially beetles, and the last remnants are broken down by bacteria. To stand any chance of fossilization, then, an animal must be buried quickly, probably within weeks of death. The most likely place for this to happen is in water—rivers, lakes and seas— where the fine sediments that settle on the bottom rapidly cover the carcass. This explains why marine fossils, like shells, are so common, and why most dinosaur have been found in rocks that were formed in rivers and lakes.
After death, the soft parts of a body, including the ligaments (p.30), break down, leaving just the bones. If the carcass had been completely buried before this happened, the skeleton would be intact. However, parts of the body are often scavenged before the body is covered, which is why complete dinosaur skeletons are so uncommon. Over time, the collagen breaks down, so the bones become brittle, like the one you baked in the oven. Depending on the composition of the sediments covering the skeleton, minerals dissolved in the water may seep into the pores of the bone. These minerals may then form crystals, sometimes filling all the spaces.
A
AAAAAA! krdo mamuta iza mene!
A PIECE OF ALLOSAURUS BONE
A 100-YEAR OLD PIECE OF HORSE BONE
The bones of an Allosaurus skeleton I examined had all its marrow cavities filled with amethyst crystals. This magnificent purple mineral, a variety of quartz, is used in jewellery. The microscopic spaces in the bone were filled too, making the bone as heavy as stone.
MICROSCOPIC APPEARANCE OF THE ALLOSAURUS BONE
9