The cambrian explosion resulted in the evolution of more than 17,000 species of an animal known as the trilobite. the shear number of trilobite fossils found in modern times suggests that trilobites were very abundant, perhaps the rulers of the seas. today, no living descendants of this group exist. what happened?

Trilobites were the early group of marine arthropods and survived on earth more than dinosaurs. The Cambrian explosion resulted in the evolution of more than 17,000 species of an animal known as the trilobite.

Today there are no descendants of this group exists because they got extinct along with other marine species 252 million ago due to mass extinction called Permian extinction.  

This mass extinction occurred due to the massive volcanic eruption one by one which makes the ocean warmer and depleted almost all the oxygen from their environment. Acidity and toxicity in water also reached a very high level. So due to all these factors almost 95 % percent of marine species along with trilobites gone extinct.