10 Terrific Facts About Trilobites
For nearly 300 million years, these ancient mariners dotted our ocean floors—surviving, thriving, and fossilizing beneath the waves.
1. OVER 20,000 SPECIES ARE CURRENTLY KNOWN.
Every single continent has yielded trilobite remains. The biggest species (Isotelus rex) was some 28 inches long, while the smallest measured less than a millimeter from end to end. Some sported defensive spines, while others had smooth, rounded shells. And whereas certain trilobites came with disproportionately large eyes, many deep-sea species were blind.
2. TRILOBITES FIRST APPEARED AROUND 540 MILLION YEARS AGO.
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.
3. MANY WOULD CURL UP INTO LITTLE BALLS FOR PROTECTION.
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.
4. AT FIRST, SCIENTISTS DIDN’T KNOW WHAT TO MAKE OF THEM.