Fossil Record

Everything that we know about dinosaurs has been worked out from their fossils. Most fossils are of tough teeth and bones, which have been buried and gradually turned to stone by minerals replacing the once-living tissue. This usually happens under water, so fossils of sea creatures are much more common than fossils of land animals like dinosaurs. Many dinosaur species have left only fragmentary fossils, such as a few teeth or the odd leg bone. It is also very rare for soft tissues like skin to be fossilized. So the "fossil record" is incomplete, and many details of dinosaur anatomy are unknown.

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Live dinosaur is chased into a slow-flowing river, where it . drowns and sinks into the mud

▲ EXPOSED FOSSiL

soft tissues rot away, but the skeleton of the dinosaur stays more or less intact

Fossil dinosaur bones are usually surrounded by rock that must be carefully chipped away during excavation. Sometimes the rock is softer than the fossil, and some fossils found in deserts can be exposed by simply brushing away the sand. But excavating fossils from hard rock takes days of painstaking, detailed work.

Millions of years later, the ancient landscape has been buried, and new types of animals have evolved

SURfACE ERoSioN

exposes the fossilized bones, which can then be excavated by fossil hunters

Live dinosaur is chased into a slow-flowing river, where it . drowns and sinks into the mud

▲ EXPOSED FOSSiL

soft tissues rot away, but the skeleton of the dinosaur stays more or less intact

Millions of years later, the ancient landscape has been buried, and new types of animals have evolved

SURfACE ERoSioN

exposes the fossilized bones, which can then be excavated by fossil hunters

Split rock reveals the empty mold of a Jurassic ammonite, a marine animal related to the cuttlefish

MOLD FOSSIL

- Deeper sediments may contain the fossil remains of much earlier life forms

U WHAT IS A FOSSIL?

A typical dinosaur fossil is the result of the animal's dead body being buried in wet mud before it could be scattered and destroyed by scavengers. The flesh usually decays to nothing, but the skeleton may survive long enough to be preserved. It may harden into stony fossils, or the mud around it may become solid rock that retains an impression of the bones.

Skeleton has fossilized and lies buried beneath more recent sediments

Skeleton has fossilized and lies buried beneath more recent sediments

Split rock reveals the empty mold of a Jurassic ammonite, a marine animal related to the cuttlefish

MOLD FOSSIL

Most animal and plant remains are completely destroyed before they can be turned into fossils. But sometimes the mud that surrounds a buried organism hardens so quickly that it forms a perfect mold of its shape. As the hard mud turns to stone the original organism disappears, leaving a cavity in the rock. This may fill with another material to form a cast.

- Deeper sediments may contain the fossil remains of much earlier life forms

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