Produced by the Population Genetics and Evolution class, Furman University

The Cambrian: Trilobites
Trilobites are a very large and diverse group of extinct marine arthropods. They first appeared in the fossil record during the early Cambrian, and go extinct in the Permian at the end of the Paleozoic Era. Due to their wide range of habitats and easily fossilized remains, the fossil record has revealed nine orders of trilobites and somewhere between 10-15,000 species. The large amount of diversity in trilobites is attributed to their biomineralized exoskeletons, made of two layers of low magnesium calcite. The name trilobite means "three-lobed", referring to the division of their bodies into a main axial lobe with a pleural lobe on either side. The exoskeleton is divided into three sections from front to back: a cephalon (head capsule), thorax, and pygidium (tail), all with differing degrees of segmentation. Although some may have been pelagic, most trilobites were benthic bottom feeders living off of detritus. Their distinctive, large, compound eyes gave them a view of approaching predators. Many species have long spines to defend themselves against predators; these spines would have been particularly effective when they rolled into a defensive ball. There is dispute over their placement within the phylum Arthropoda. Much of this is due to the lack of easily traceable ancestors from the Precambrian era. It’s believed that their closest extant relatives are chelicerates like spiders, scorpions, and horseshoe crabs (Virtual fossil Museum 2010). 

Page by Megan Aprill
Trilobite Fossil Photo credit: Gon SM. 2007. Gallery of Proetida.

Hughes, NC. 2007. The evolution of trilobite body patterning. Annu Rev Earth Pl Sc 35: 401-434.

Waggoner B. 1994. Introduction to the Trilobita. University of California Museum of Paleontology (UCMP). Accessed 30 Jan, 2010.

The Virtual Fossil Museum. Trilobita – Trilobites. Accessed January 30, 2010.