What are the ancestors of the trilobites?
Ancestors of trilobites would be arthropods in the same broad group to which trilobites belong (the Arachnomorpha) but lacking one or more of the characteristics that distinguish trilobites. Perhaps one of the most important trilobite characteristic feature is exoskeleton calcification. Without a calcified skeleton, the chances of fossilization are extremely low. This may explain why the ancestors of trilobites are not clearly known. Arachnomorph groups such as the Helmetiidae, Naraoiidae, Tegopeltidae, and Xandarellidae might resemble the ancestors of trilobites. Each of these is uncalcified, and only rarely preserved, as at the Burgess Shale in Canada and Chengjiang, in China.
