What Is a Fossil Record?
The fossil record is a chronologically ordered history of life on Earth based on fossil finds and scientific study. It has particular importance in the study of how plants and animals evolved and how they may be related to each other.
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Fossils
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Fossils are physical evidence of organisms that lived long ago, sometimes preserved as skeletons, such as dinosaurs. Others are found as impressions, such as footprints in sandstone, or whole organisms frozen in time, such as insects in amber.
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Evolution
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Evolution is the study of how organisms have changed over time. These changes are in the form of DNA changes or mutations. These mutations, if they enhance survival, occasionally develop into a new species.
From Sea to Land
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The fossil record shows that fossilized remains of land-based organisms can be found in rock up to 370 million years old. Fossils of sea creatures are older. Proof of the transition from sea to land was found in 1998 by the discovery of a fossil fin dating from 370 million years ago showing a hand-like skeletal structure.
Reptiles to Mammals
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The fossil record also shows mammals appearing 230 million years ago. Reptiles appeared 70 million years earlier. The cynodonts were reptiles dating from 260 million years ago, believed to be the ancestors of mammals based on their ear bone structure. When the mammals appeared, the cynodonts died off.
Whales
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The fossil time line also shows the more recent history of the whale's move from land back to the sea. Pakicetus is a 52 million-year-old fossil of a wolf-sized whale that had terrestrial-style teeth. It also lacked the structure that allows whales to hear using vibration. Further discoveries, particularly in Pakistan, show the gradual evolution of the whale into a true marine mammal.
Incomplete Record
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The fossil record is incomplete. There is no better example of this than in the debate over whether birds evolved from dinosaurs. The first feathered dinosaur-bird fossil, Archaeopteryx, was dated at 145 million years old. More recent fossil discoveries have found feathered dinosaurs and bird-like creatures dating both before and after Archaeopteryx.
References
- Photo Credit "fossil frog" is Copyrighted by Flickr user: kevinzim (Kevin Walsh) under the Creative Commons Attribution license.
