Fossils: A Direct Link to Macroevolution
Paleontology is used to study macroevolution, or large evolutionary trends. Fossils give us the only true evidence of the history of evolution. Fossils are bones, shells, or teeth that have been buried in rock but can also be outlines of leaves, footprints, or trails, called trace fossils. Fossils are formed when residue covers some type of material, such as bone. By piecemeal, the bone absorbs chemicals from rocks surrounding it. In the end, all that is left is basically a rock in the shape of the original material.
Fossil records and new radioactive carbon dating both help us determine the age of the fossils and the environment from which a plant or animal lived. Also, we can learn about the balance of gases in the atmosphere from which the fossil originated.
Fossil records provide numerous examples of macroevolution over huge geologic time spans. We know that certain animals roamed the Earth during different time periods and some, though most are not, are still alive today. Trilobites, crinoids and brachiopods ruled over shallow water environments in the Paleozoic era (@540 million years ago to 250 million years ago). Rocks from that era are peppered with fossils of these extinct or less creatures.
There are no trilobites alive today but during the Paleozoic era, these varied arthropods scampered about feasting on food particles from the ocean floor. With more than 15,000 species identified, they are the most variant group in the fossil record.
Crinoids are less plentiful today with only a few hundred species remaining. But during the Paleozoic era, these creatures, known as sea lilies, were very common. So much so that parts of their skeletons make up entire rocks in certain areas of the central United States, which used to be part of the shallow ocean floor. To flee from predators, today’s crinoids find homage in the deep ocean or tucked into cracks in rocks.
Brachiopods are still alive but less common today. With shells like clams for housing, they have little nets made for skimming seawater for food. During the Paleozoic era there were very diverse with sixteen plus orders and thousands of species.
The preservation of the fossils of these Paleozoic creatures enables scientists to visualize what the shallow waters of the oceans were like millions of years ago. The ecosystems and fossils are somewhat of a diary or journal of biological evolution in the shallow ocean waters and other environments as well. Paleontologists study the fossils in sedimentary rocks from various geologic time periods and locations across the globe.