The ancestors of trilobites may be arthropod-like animals, such as the Preeg worm or other trilobite-like animals of the hidden Ediacaran period. Early trilobites have many similarities with Burgess shale and other CAMBRIAN arthropod fossils, so trilobites and other arthropods may have the same ancestor before the boundary between Ediacaran and CAMBRIAN.
Trilobites developed rapidly and reached the peak of reproduction in the late Cambrian. In order to adapt to different living environments, morphological evolution is varied. Some head, chest and tail are the same size, and the shell is flat, and the head and tail lack obvious decoration, such as megacephaly): some head is wide and big, with a flat and wide edge around the front edge, on which tumor particles are arranged neatly, such as cryptotrichoma; In order to avoid injury, some people decorate their chest and tail with sharp needles, such as schizophrenia (some shells can also be curled into balls, such as cryptocephalus)
The specific reasons for the extinction of trilobites are unknown, but the appearance of early fishes with strong palates such as sharks in Silurian and Devonian seems to be related to the decrease of trilobites in the same period. Trilobites may provide abundant food for these new animals.
In addition, by the late Permian, the number and species of trilobites were quite small, which undoubtedly provided conditions for their extinction in the Permian-Triassic extinction event. Although the previous Ordovician-Silurian extinction event was not as serious as the later Permian-Triassic extinction event, it also greatly reduced the diversity of trilobites.