Trilobite fossil in matrix. Measures 3 1/2 inches by 3 inches. This little guy is in a partial roll, a defensive move common to trilobites.
For nearly 300 million years, these ancient mariners dotted our ocean floors—surviving, thriving, and fossilizing beneath the waves.
Their debut roughly coincided with the dawn of the Cambrian period. During this game-changing chapter in Earth’s history, multi-celled organisms went through an apparent explosion in diversity, or at least an explosion in life forms that leave fossils. New creatures—including a barrage of mollusks and arthropods—seem to have evolved at an unprecedented rate.
The Cambrian also saw trilobites become the most common and diverse animals on the planet. However, trilobites began to decline when the period ended some 500 million years ago. Though the invertebrates stuck around for another 240 million years, they’d never again be so successful.
When danger struck, some trilobites could ball themselves up like underwater pill bugs, with their rear end flexed under their head. Specimens dating as far back as the late Cambrian have been found in this defensive position.
Over the course of its life, a trilobite outgrew many shells. During the molting process, these discarded husks would often get preserved for posterity. One trilobite could therefore leave behind several trilobite-shaped fossils. Specimens that represent the actual creature—as opposed to its shuffled-off shell—are comparatively rare.
Some call it the “Great Dying”—250 million years ago, 90 percent of all species on earth suddenly perished. Possible causes include everything from increased volcanic activity to exploding supernovas. Regardless, the event—also known as the Permian Extinction—killed off a number of insects, sharks, armored fish, mammal-like creatures, and countless other organisms. Trilobites, however, are by far the most famous lineage to have met their end this way.
Long before Europeans first set foot on the continent, the Pahvant Ute people, from what is now called Utah, gathered Cambrian trilobites. Believing that the fossils harbored special powers, the natives carried them around as protective charms. These odd, petrified critters were given the name “Timpe-Konitza-Pachuee,” or “little water bug living in a house of stone.”