But R. rex was not the largest trilobite. That goes to Isotelus rex, which measures nearly 30 inches long. But R. rex emerged far earlier on in the Cambrian Period.

The "Puzzling the Past" exhibit showcases collections of these unique specimens to explore Earth's geologic history.

The reconstructed fossil claw of ancient sea scorpion, Jaekelopterus rhenaniae (e) and its size relative to a human male and to the sea scorpion (a), the trilobite Isotelus rex (b), the dragonfly ...