How do dinosaur fossils form? | Natural History Museum

How do dinosaur fossils form? | Natural History Museum


Millions of years ago, this dinosaur was going
about his normal daily life. But his day went from good to bad. REALLY
bad. After he died, other dinosaurs ate him. And the rest of his skin and muscles rotted
away, leaving just his bones. These were quickly buried by mud. Over millions of years, more layers landed on top – mud, sand and even volcanic ash. This added up to a lot of weight on top of
the skeleton. Some parts got crushed. The layers of mud, sand and ash turned into
hard sedimentary rocks. While this was happening, water seeped into
the bones. It left behind minerals, turning the bones to stone and creating a fossil. Earth changed a lot over millions of years. Rocks that were once deep underground rose
to the surface, a process called uplift. Very slowly, wind, water and ice wore away
the rock. Eventually, bits of the fossil skeleton were
exposed and became visible on the surface. Fossils are constantly getting eroded out
of rock. Most are lost. But if we’re very lucky, someone will find
one. Nearly all of all of the fossils we find – around 99% are from marine animals, such as shellfish
and sharks. This is because they lived in the sea, where
sand or mud could bury their remains quickly after they died.
But dinosaurs live on land, so how do they get buried so quickly?
Most dinosaur fossils we find belong to animals that were living near to a lake or a river.
They died and a short while later the area flooded, covering their remains in mud and
silt. Occasionally, something more dramatic happened. In one example, two dinosaurs – Protoceratops
and Velociraptor – were fighting in the desert. They were mid-battle when, suddenly, a sand
dune collapsed on top of them. Their fossils show them frozen in their fighting
poses. In another tragic example, the feathered
dinosaur Citipati was sitting on its nest of eggs when a sandstorm blew in and covered
it. Fossils like this – from animals that were
alive when they were buried – are really rare. It’s not just bones that turn into fossils.
Dinosaurs can also leave behind footprints and impressions of skin and feathers. So next time you’re near some sandstone or mudstone, think of what fossils could be hiding,
just waiting to be discovered. It probably won’t be a dinosaur fossil, as
they’re so rare. But it could be a prehistoric sea creature like an ammonite, which went extinct at the same time as dinosaurs, many millions of years ago.

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