What are fossils?
Fossils are the preserved remains of ancient organisms. Animal fossils include:
- actual parts of the body, such as bones or an entire skeleton;
- traces left by the body, such as a trail of footprints.
Harder tissues, such as bones and teeth become preserved as fossils more often than softer tissues. This is because softer tissues such as skin and flesh, are more likely to be eaten by animals or decay before they can be preserved.
Our ancestral fossil record
More than 2000 ancient individuals are now found in our ancestral fossil record. Some of these individuals are represented by reasonably complete fossil skeletons. However, this is relatively rare, particularly for our older ancestors who lived millions of years ago. Generally, individuals who lived more recently tend to have more complete fossil skeletons than those who lived longer ago. Often only a handful of fossil bones or bone fragments are found and sometimes all that remains of a particular individual is a single tooth!
Jaws and teeth
Jaws and teeth are the most commonly found fossils. These are especially hard parts of the skeleton and therefore have a better chance of lasting long enough to become fossilised. The numbers, types and shapes of the teeth tell us much about the diets, lifestyles and relationships of their owners. They can even help indicate an individual’s age at the time of death.
Skulls can provide details about the size and shape of the brain, face and teeth. The base of the skull can also provide information on posture as it shows how the head was supported on the body.
Bone fossils can provide information about some of the soft body tissues that did not become fossilised. Surface markings left on the bones show where muscles, tendons and ligaments used to attach and where blood vessels and nerves used to lie. They can also provide information about how tall and how heavy the individual would have been. The limbs can also tell us how their owners moved about.
Sand and mud can fill a fossil skull and then harden to produce natural fossil endocasts of the brain cavity. This preserves the size, shape and surface features showing different regions of the brain, blood vessels and brain folds.
Finding their fossils
Most of our ancestors’ fossils are found in sites that were once on the margins of ancient lakes and rivers, inside caves or were subject to volcanic eruptions. In some sites, the conditions needed for fossilisation occurred over relatively short time spans. In others, a rich fossil record accumulated over millions of years.
Fossils of our earliest ancestors have only been found in Africa, especially in the Rift Valleys of East Africa and in limestone caves in South Africa. On other continents, our ancestors’ fossils are mostly less than about one million years old. They are especially found in caves in the Middle East, southern Europe, and parts of Asia, including India, China and Indonesia. Remains (often unfossilised) younger than about 40,000 years old are found in Europe, Australia, Flores in Indonesia, and the Americas.