Page 20 - DINOSOUR ATLAS

Dinosaur atlas
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.

Live dinosaur is chased into
a slow-flowing river, where it u exposeD fossil
drowns and sinks into the mud
Fossil dinosaur bones are usually surrounded
by rock that must be carefully chipped away
during excavation. Sometimes the rock is softer
soft tissues rot away,
but the skeleton of the than the fossil, and some fossils found in
dinosaur stays more deserts can be exposed by simply brushing
or less intact 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

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

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

, MolD fossil deeper sediMents
may contain the
Most animal and plant remains are completely destroyed fossil remains of
before they can be turned into fossils. But sometimes the mud much earlier
that surrounds a buried organism hardens so quickly that it life forms
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.
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