How many kinds of fossils are there?
Fossils are an important source of information. Whether it is a body fossil, like a shell or bone, or a trace fossil, like a dinosaur footprint or coprolites (petrified animal droppings), each one has a story to tell. ey can tell us a lot about plants and animals that lived a long time ago and the environments in which they lived. Many fossils look a lot like plants and animals with which we are familiar, but some are like no living thing we’ve seen before. There are several ways a fossil is made. Sometimes a bug gets caught in tree sap. e sap covers the bug and preserves it. at’s a fossil. Sometimes an animal may get stuck in tar. Their bones are preserved in the tar. ose are fossils, too. Read on to learn more about other kinds of fossils and how they are formed. Body Fossils Usually, when a plant or animal dies, it rots, leaving no trace that it ever existed. But when conditions are right, a fossil forms. When a plant or animal dies and sinks to the bottom of a body of a large body of water, the soft parts rot away. The skeleton settles on the floor of the body of water. Sand and mud cover it. As time passes, more and more mud and sand build up, putting pressure on the skeleton. This pressure turns the skeleton into a rock. If the rock stays buried long enough, it dissolves and the skeleton leaves a hole shaped like the animals bones. Then, water fills the cavity. Minerals in the water crystallize inside the hole and make a cast. It’s the same shape as the skeleton, but the skeleton isn’t there anymore! Later, as the earth shifts and changes through things like earthquakes, shifting coastlines, mountain building and other events, the fossil is brought to the surface. Trace Fossils Footprints, skin prints, burrows, eggs and even animal waste can sometimes be fossilized. These fossils often tell scientists about the behavior of the animals that made them. Skin prints and footprints become fossils when an animal makes an impression in a muddy area. Then the mud is buried, and the imprint turns into stone. Footprint fossils are useful because they tell scientists about how the animal walked and if it likely lived alone or in a group. It’s not always easy to match a footprint to a particular species of animal though. Coprolites, or fossilized droppings, are especially useful because scientists can learn a lot about what an animal ate. Sometimes the coprolites include things like plants and spores from species that no longer exist. It can also reveal things about the size of the animal that left it.
