How Are Imprint Fossils Formed?

Ancient Life

• The first step in making an imprint fossil happened millions of years in the past. An animal or plant makes an imprint in soil during its lifetime, or with its body when it dies. The ideal place for these imprints is in shallow water, where sediment or mud can build up and harden into rock over millions of years.

Imprints to Fossils

• Imprints are best formed in wet soil or mud. Once an imprint has been made the soil is dried out by the sun and turned to rock over millions of years. Fossils formed in mud are much less common than fossils formed by sediment, because of their fragile and exposed nature.

Animals to Fossils

• In the case of fossils formed from entire animals, sediment will cover the animal and slow the natural process of decay. Over thousands of years the sediment covering covering the animal turns to rock and the animal inside decays, forming a mold of its original shape. This space is then filled by minerals to create a shape just like that of the animal, a process known as fossilization. Because the ideal environment for fossil formation is in water, the most common imprint fossils are those of sea creatures.

Types of Rock

• Today imprint fossils are most likely to be discovered in limestone, shale or sandstone rock. These types of stone form from sediment in shallow water where ancient plants and animals are best preserved. Some of the best places to find fossils are riverbeds and beaches near limestone cliffs, because the action of the water is always exposing new areas of rock.

Famous Fossils: Hadrosaurus foulkii

• In 1858 William Parker Foulke discovered the first scientifically recorded dinosaur remains in Haddonfield, New Jersey. He spent an entire summer with hired workers digging in shin-deep gray slime before discovering the remains of an animal, roughly the size of an elephant, with structural features similar to those of lizards and birds. His find, known as Hadrosaurus foulkii, was an example of fossilization as a result of the dinosaur's being buried in sediment. To this day it is the only known hadrosaurus fossil in the world.