The theory of evolution states that individuals within a species show wide degrees of variation, and those individuals with characteristics best suited to their environment are more likely to survive and reproduce. This theory grew from studying the variations and similarities in living animals and plants, but also, very importantly, by studying fossils.
The study of the number and placement of fossils within certain types and areas of rock is known as the fossil record. This record gives us an indication of the types of animals and plants that existed in the past, from many millions of years ago, right up until around 10 000 years ago.
Fossils of single celled organisms such as cyanobacteria from Australia have been found in rocks that are more than 3.5 billion years old! Palaeontologists are people who study fossils. By comparing fossilised body structures and fossilised tracks of movement, they painstakingly piece together the story of how animals and plants have changed and evolved over time.
Importantly, by comparing fossils from different species, palaeontologists can look for similarities in structure, to try and work out which species are related to which others. This work has enabled scientists to visualise how some species have evolved from others.
The discovery of “transitional” fossils has greatly assisted palaeontologists’ understanding of how evolutionary processes occur. For example, in 1998 scientists found a 370 million year old fossilised fish with a hand-like fin, suggesting a transition from sea dwelling creatures to land. Meanwhile the discovery of transitional reptile fossils with mammal-like jaw bones has enabled palaeontologists to date the emergence of early mammals to about 245 million years ago. Mammals did therefore live alongside the dinosaurs.
Fossil evidence even has allowed us to identify where humans and chimpanzees went their separate ways. Our last common ancestor lived about 5-7 million years ago. Since that time fossils of over 20 hominid species have been discovered!
Tracing the lineage of plant and animal species using the fossil record is not an exact science. The lack of transitional fossils makes this all the harder, leading to significant “gaps” in the fossil record. Because the formation of fossils is a rare event, many transitional species have just not formed fossils. However, as new fossils are being discovered all the time, we can expect at least some of these gaps to be eventually filled.
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