V >> Glossary Index
|F|| An audio file is available.|
| View printable page version.|
Theropods had feet with three toes and a dew-claw although segnosaurs had
four big toes on each foot. Each toe had talons or claws that might have
been used to catch and kill prey. Fossilized theropod tracks resemble those
of modern birds. Sauropods had huge feet that resembled those of the modern-day
elephant. Ornithopods had thick toes with hoof-like nails.
A fossil is a part of a plant or animal that has been preserved in stone.
Over millions of years, the animal or plant tissue is replaced with minerals
dissolved in water, until the original organic form is recreated in stone.
Fossils form when a dead animal is covered with layers of mud or sand.
Much of the skeleton can be transformed to stone, although the smaller,
lighter bones are often lost. Under the right conditions, the skin itself
may leave an impression, and sometimes even the food the dinosaur consumed
just before it died may be fossilized. By using the carbon 14 process and
other dating methods, scientists can determine the age of a fossil and
thus tell when the dinosaur lived. From fossils, scientists learn enough
to reconstruct a model of the dinosaur.
Frills, like large shields, protected the necks of ceratopsians. There
is a correlation between shield and horn size. Those ceratopsians that
had small heads and small frills had small or non-existent horns. In turn,
the large-frilled ceratopsians, such as Triceratops, had large horns. The
largest known frill is that of Torosaurus, whose frill was 5 feet (1.6
meters) long. Its head was a massive 8 feet (2.4 meters) long.