Trilobites are primitive arthropods that lived from the Cambrian (521 mya, possibly earlier due to ghost lineages) to the end of the Permian (250 mya). Their size ranges from smaller then your hand to being as long as a normal human height, and in the entire class (Trilobita) there was 11 clades in total, ranging from the eyeless Agnostida to the late surviving Proetida. In this documentary, they appear in Death rays, Hell on earth and The Great Dying.
Once the gamma ray burst hits, trilobites (possibly Isotelus) struggle to survive due to radiation and lack of oxygen. They are some of the organisms that survived the extinction, despite some blows. They still are being fed on by Eurypterids and Straight-shelled nautiloids.
Hell on earthEdit
The trilobites (presumed Leonaspis) face extinction again, except now their not big as they used to be. Yet however they survived this extinction, but this causes a long-term decline in species count before their inevitable extinction in the Permian/Triassic event.
The great dyingEdit
The trilobites (likely a proetid) face extinction again, this time the biggest mass extinction on earth. This time, the trilobites weren't so lucky; they went extinct primarily due to the fact that they were already declining; by the time the Permian extinction happened, there was only a few species left.