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What Are the Five Most Common Fossils?

Fossils can be found all over the world, even in your backyard. While enormous dinosaur fossils draw crowds to museums, the fact is most fossils are much simpler and smaller than those large creatures. Because large parts of what is now the United States once lay under the sea, many fossils are of sea creatures.

Trilobites
- Trilobites are an extinct group of organisms distantly related to insects and lobsters that lived under the sea. They were segmented creatures with jointed appendages and an exoskeleton. They had complex eyes and their exoskeletons have three sections. They were bottom feeders who lived from 500 million years ago to 270 million years ago, and over that period developed a variety of different species
Brachiopods
- Brachiopods are a phylum of sea creatures that largely went extinct 250 million years ago, but some species survive today. Shells of unequal size cover brachiopods, making them look similar to clams, although they are not related to mollusks. They feed by filtering food similar to clams, oysters and other shelled creatures. They lived on the sea floor.
Corals
- Rugose corals and tabulate corals are two orders of corals that went extinct around 250 million years ago. Rugose corals are also known as horn corals because of their hornlike shape. They lived on the sea floor or in reef structures and ate microscopic prey by stinging them with special stinging cells. Tabulate corals also lived on the sea floor or on reefs and grew in stacks of large horizontal groups called tabulae, where they get their name. They, too, caught microscopic prey from their stationary position.
Mollusks
- The Mollusca phylum of creatures, which includes clams, snails and squid, make up a large number of fossils. Many mollusks survive in great numbers to this day and are one of the most successful groups of marine invertebrates. Mollusks are unsegmented soft-bodied animals that typically have a shell or shells. Bivalve fossils, a group of mollusks that include clams, are different from brachiopods in that their shells are mirror images of one another rather than uneven. Their shells and the shells of other mollusks often survive in fossil form.
Crinoids
- Crinoids are a class of sea animals related to sea stars and sea urchins. They are also known as sea lilies because of their distinct shape, which consists of a long stalk of tiny calcite plates topped with a head and feathery arms, giving the creature a flower-like shape. While some species of crinoids survive today, they largely went extinct 250 million years ago during the same extinction event as the brachiopods, trilobites, and other creatures mentioned. Crinoids were once so numerous that some limestone beds are composed almost entirely of the fossilized remains of crinoids.

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