Lifestyles
During the long evolutionary history of the trilobites, taxa evolved to inhabit a wide variety of ecological niches within the ocean habitat. Some were pelagic and lived within the water column, while others were benthic and lived on the ocean floor where they walked around the surface or burrowed beneath the substrait. During the Late Cambrian, some trilobites made use of a newly-evolved environment and became reef-dwelling. Some studies also suggest that a few trilobite species were even parasitic and lived off of a host organism. Trilobites were extremely successful in utilizing the environment that they inhabited, and as time progressed, many acquired specialized adaptations to further aide in survival. Larger eyes and a more sleek body plan helped the pelagic forms to move throughout the water column with more ease. Elaborate spines may have aided benthic forms to spread their weight over a greater area while at rest on the sea floor bottom, while also possibly giving protection against predators. As what is generally the case in the fossil record though, the more specialized an organism is to a particular environment, the more it is in peril of extinction. As such, highly specialized trilobites inevitably didn't last very long and tended to go extinct much faster than more generalized species.
In addition to the wide variety of locomotion methods trilobites used to maneuver through their various niches, they also utilized a number of feeding habits. Some were filter-feeders while other were planktivores, although the majority of trilobites were most likely predators and scavengers...or a combination of the two. Species with an inflated / enlarged glabella ( a large central plate on the cephalon) are generally considered to be predatory. The larger trilobite species are also very-likely to be predatory. Smaller Middle Cambrian species (namely Agnostid) are considered to be examples of the filter-feeding habit.
Many trilobites were able to roll their bodies much like some current crustaceans or "pill bugs" that we find in the garden. This ability to form a body into a ball shape is called spheroidal enrollment. Early Cambrian trilobites had poor enrollment abilities. Proper enrollment was fully achieved in Late Cambrian species, while Ordovician and later groups expanded the ability and developed intricate enrollment patterns. Some trilobites are commonly found fossilized while enrolled, most notably the order Phacopida.
Phacops (enrolled) -
Devonian, Morocco
Comura bultyncki - Devonian, Morocco
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