Temporal range: Middle Ordovician–Late Ordovician
Isotelus brachycephalus as it appeared in Sea Monsters
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita
Family: Asaphidae
Genus: Isotelus
  • Isotelus brachycephalus

Isotelus is a genus already known for its abnormally large trilobites. However, one species, Isotelus rex, is known to be the largest trilobite ever discovered, reaching the insane length of 28 in.


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The largest species, Isoletus Rex has been found in states in Western North America, and probably lived in lakes, ponds, or other sources of stable water. Trilobites might've lived with other fishes, ammonites, and amphibians. They likely lived in oceans and large open bodies of water however.