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Trilobites-Paleozoic Arthropods

The Trilobite was an early arthropod. It came into existence approximately 540 million years ago at the beginning of the Paleozoic Era in the Cambrian Period. It flourished in the ancient seas for close to 300 million years.


Trilobites were among those animals that seemed to burst on the scene at the beginning of the Cambrian Period. The number of species increased rapidly through out the Cambrian and into the Ordovician period, but suffered a steep decline at the end of that period. Their numbers never recovered.  The last trilobites died of at the end od the Permian Period about 250 million years ago.

The trilobite’s hard exoskeleton, segmented body and jointed legs are the characteristics that place it in the Phylum Arthropoda. It sets itself apart as a class from the other arthropods by the three lobes that run the length of the animal’s body. In addition to the three lobes, the body plan had three distinct parts: the head, called a cephalon, a tail called a pygidium, and a flexible middle section called a thorax. Trilobites put this flexibility to good use. They could roll up into a ball for protection.

Like other arthropods, trilobites had to molt in order to grow. They split the exoskeleton at the front of the head and crawled out. The new exoskeleton slowly hardened as it became mineralized. 

Trilobites lived in a wide range of climates, from warm shallow seas to deep icy ocean shelves. The wide variation of more than 25,000 species is often characterized by different body structures and eating habits, including predatory, filtering, and scavenging. They filled every marine habitat, some swimming freely in the water column, while others crawled along the ocean floor. Some even burrowed into the sediments.

flexi-calimene Trilobite

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