Page 20 - Dinosaur (DK Eyewitness Books)

Limestone How do we know?

WȦ ȬȯȰȸ ȸȩȢȵ ȭȰȯȨ ȥȦȢȥ ȥȪȯȰȴȢȶȳȴ were like because
paleontologists have dug up their remains. Most of these
belonged to corpses buried under mud, sand, or volcanic ash that
slowly hardened into rock. Minerals filled pores (spaces) in the
bones and hardened them, or replaced them altogether, turning
bone to stone, in a process called permineralization. All that is left DIGGING UP THE PAST
Paleontologist Luis Chiappe
are usually fossilized bones that have been buried in the ground
Sandstone for millions of years. Sometimes, though, the shapes of a body’s at Ukhaa Tolgod in Mongolia’s
excavates a Protoceratops skull
Gobi Desert. Determined
soft parts—skin, tendons, and
dinosaur hunters sometimes
muscles—have survived, travel halfway around the world to
reach the best bone beds. There
giving scientists precious, they must often camp and work
rare glimpses of soft anatomy. in harsh conditions and put up
with scorching heat or bitter cold.
Dinosaur at
riverbank Bones of recently
Shale deceased
dinosaurs

Layers
Volcanic ash up on top
building

Limestone

Volcanic ash

Stack of
layered rocks

Dry riverbed
Shale ROCK LAYERS Dinosaur
Fossils occur in sedimentary rocks. These are formed
when sediment (sand, mud, and gravel) builds up in fossil in rock
layers and is compressed over many million years. A
series of sedimentary layers can be exposed in a cliff
face (as shown here). In an undisturbed set of layers, THE STORY OF A FOSSIL
the oldest rocks lie at the bottom and the youngest From left to right, these block diagrams
at the top. Knowing this, scientists can work out tell the story of dinosaurs that drowned in a
the relative age of each rock layer and the fossils it river. Their flesh rotted away, leaving only bones
contains. Index fossils are fossils that are characteristic in wet mud when the river dried up. Later, the river
of a particular period and help to date the rocks refilled, adding more sediment, and buried the bones
in which they are found and also other fossils in deeper and deeper in mud that slowly turned into rock.
Limestone are index fossils for the Mesozoic Era. Scientists into fossils. Over millions of years, wind and rain wore
Minerals seeping into pores in the bones changed them
neighboring layers of rock. Ammonites, for instance,
also date rocks accurately by measuring the decay
away the rocks, leaving the dinosaur fossils exposed on
the surface. There, dinosaur hunters discovered them.
of radioactive elements in them.
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