© Stephen Gatesy, Brown University
A theropod foot at three stages in creation of a deep track.
In general, the bigger the animal, the less its footprint resembles the bony structure of its foot. The reason? Large animals need a lot of built-in foot padding to absorb the impact of their great weight.
Judging from their huge footprints, the immense feet of the plant-eating dinosaurs called sauropods were fleshy, covered with tough skin and cushioned by thick pads--like those of modern elephants. As a result, some sauropod prints are almost as featureless as a toddler's backyard wading pool--in stone.
© Mark Hallett
Consider the right rear foot of the sauropod dinosaur Diplodocus. Three of its toes end in claws, which may be visible in footprints. The rounded bone is the animal's heel, which was cushioned by a thick heel pad the size of a basketball. Diplodocus walked on its toes, rather as if it were wearing a giant wedge-heeled shoe.
AMNH SPECIAL COLLECTIONS.A young footprint enthusiast demonstrates the size of one of the sauropod footprints discovered in Texas in the 1930s and 40s.
Fast Facts: Diplodocus longus
- Pronunciation: "Di-PLOD-oh-kus LONG-us"
- LENGTH: about 25 meters (82 feet)
- WEIGHT: 9-18,000 kilograms (20-40,000 pounds)
- Food: plants
- When it lived: about 150 million years ago
Footprints may record not just the shape of an animal's foot but the consistency of the ground on which it walked. The appearance of a single animal's footprints may vary greatly depending on whether the soil was dry or sticky. This can make identification of the trackmaker a challenge.
But the print left when a walking animal sank deep into the mud can be informative too. Because the sediment surrounded the foot, it may preserve more details about movement and anatomy than a print on the surface.
Fast Facts: Coelophysis bauri
© J. Sibbick
- Pronunciation: "seal-o-FYE-sis BORE-eye"
- LENGTH: between two and three meters (about 6-10 feet)
- WEIGHT: about 45 kilos (100 pounds)
- Food: small reptiles and fish
- When it lived: about 215 million years ago
- Fun fact: In Coelophysis trackways the prints are often widely spaced. Perhaps these animals were often in a hurry.