Dinosaur Definition
Over six hundred types of dinosaurs are known and more are being identified
all the time. Dinosaurs are defined as land-dwelling reptiles living in the
Mesozoic era of Earth history that shared a specific anatomy. The true dinosaurs
had hips, legs, and ankles structured somewhat like a bird’s, so the legs moved
under the body rather than out to the side like modern lizards. Dinosaurs
differed from ancient reptiles because dinosaur skeletons were able to support
large, running bodies. Prehistoric animals such as the flying Pterosaur or the
swimming Plesiosaur were not dinosaurs because their body structure was very
different from dinosaurs, and they did not live on land. Before the dinosaurs,
another group of reptiles lived that had features in common with mammals, so
they are classified with the dinosaurs.
It is difficult to match specific animals to prints, but we can often
determine a group of animals that possibly made the track. Dinosaurs are divided
into two main groups, Saurischia and Ornithischia, according to
the shape of the hip. The Saurischia are more lizard-like and include
Tyrannosaurus rex and Velociraptor. They divide into a meat-eating
group and a plant-eating group. The Ornithischia were more bird-like, and
all plant eaters. They include Stegosaurus and Triceratops.