As we’ve said previously, the AMNH has an awesome Trilobite website.  Today, we want to highlight the one about Trilobite Enrollment.  It is generally accepted that trilobites enrolled to protect themselves from predators and other potentially other events in the surrounding environment.  This page has a good discussion about the history and the usefulness of enrollment.

There is a story that has become part of trilobite folklore. It tells of how back in the early 1970s, a Berber tribesman living on the edge of Morocco’s Sahara Desert was walking near the mountains that encircled his home. As he was strolling past one, he heard the distressing sound of falling rocks and noticed a particular fist-sized piece that was cascading in his direction down the mountainous slope. 

Out of curiosity, he bent to investigate what the mountain had yielded, and much to his surprise, he found a perfectly enrolled Drotops trilobite lying at his feet. The unexpected discovery intrigued the Berber and empowered him to seek the spot from which this “strange rock” had originated. For weeks he searched, climbing and exploring, until finally he found the fossil-bearing layer upon the Magic Mountain that would soon ignite the entire Moroccan trilobite explosion.

This tale serves as a somewhat roundabout means for us to broach the subject of trilobite enrollment and ask some very basic questions… why did these primitive arthropods enroll… and when did they begin to do so? Of course, many modern creatures from isopods to armadillos enroll for safety, and it can be logically surmised that trilobites assumed such a defensive position for much the same reason. With their thick calcite shells, an enrolled trilobite could present quite the daunting challenge for any predator seeking an easy meal. In addition, the compact shape provided by enrolling may have also aided them in battling unfavorable conditions during the heights of oceanic storms.