Trilobite

Trilobites swarmed through the ancient seas 500 million years ago. These arthropods (age group that includes modern crabs and lobsters) were the first animals known to have eyes; this enabled them to see their surroundings and hunt the way modern sea creatures do now. Trilobites survived in the oceans for 300 million years, making them one of the longest surviving species in history.

Bottom Feeder:
The trilobite's body was divided into as many as 44 segments. Under each segment was a pair of legs. These jointed limbs helped the creature scurry quickly along the seabed where it found its food.

Call Him Gill:
Also attached to the leg were threadlike filaments that acted as gills. They were not very efficient, so the trilboite needed a great number of these 'gills' to absorb the oxygen it needed from the water.

Creature Features

 * Species: Various
 * Size: Length up to 2.5 ft.
 * Prey: Plankton, worms and other trilobites
 * Where? Fossils have been found everywhere a sea once existed
 * Sound Off: TRY-low-bite

Did You Know?
The closest living relative of the trilobite is the horseshoe crab.

Crystal Clear
Trilobites are belieed to be the first creatures to develop eyes. Their complex eyes were made of crystals of a mineral called calcite. Clear calcite lets plenty of light through, so the trilobite had good vision to look for prey. Many rows of these crystals lined up to form any-where from 100 to 15,000 lenses in each eye. Sme trilobites had eyes on the top of tall stalks s they could stay buried in the sand and watch prey or

The Spice of Life:
Trilobites came in all shapes and sizes, ranging from 1 millimeter to 2.5 feet in length. Scientists know of more than 15,000 species of trilobite, and the list is still growing.

Change is Good:
Jawed fishes, including early sharks, appeared in the seas about 400 million years ago. Masters of adaptation, some species of trilobite developed sharp spines on their backs to combat these new predators.

Timeline:
Trilobites lived 550 to 250 million years ago, throughout most of the Paleozoic Era.