The Trilobite
Adapted to Multiple Marine Environments

The Trilobite was a marine animal, meaning that it lived in “salt water,” but certainly Paleozoic Era “salt water” was chemically much different than that of today’s oceans. Fossils have been found in rock formations that indicate a wide range of temperature, from shallow tropical seas to deep, cold ocean shelves.

Most of our ideas about the life of trilobites are based on observations of their body structures. This differs significantly in various species suggesting a variety of locations and eating habits. Some bodies seemed designed for burrowing into the sea bottom or benthos. Others’ bodies appeared to be suited for crawling along the sea floor or coral reefs in search of prey. There are even trace fossils that show tracks left by the trilobite ending at a poor worm’s burrow door! Some species’ body plans made them capable of swimming in the water column and spending little time on the ocean floor.

Perhaps the most interesting ability of the trilobite was enrollment: its capacity for curling itself into a “ball.” It's thoracic exoskeleton is made of sections, like the ridges in an expandable watch band. The flexible material between these ridges allowed the thorax to bend. The cephalon and pygidium then fit together, often perfectly matched so all the legs and antennae would be protected securely inside the exposed exoskeleton. Sometimes this rolling left the sharp points of a specialized cephalon or pygidium exposed to fend off would-be predators. Perhaps enrollment had other purposes, as well. Surely this posture would have allowed a trilobite swimming in the water column to change depths very rapidly. Regardless of the purpose, enrollment is a fascinating ability that we can observe in the many fossils that have been preserved in various stages.

The diets available in these different habitats would have been a reflection not only of the habitat, but also of the body plans of the trilobites that inhabited them: sort of a chicken and egg question. The body types that would have worked best crawling around on the ocean floor would have been particularly suited to scooping up detritus (organic debris), worms, and other small invertebrates.

Some body structures were designed to filter through the sand. Their bodies contained gills that helped gather the food from the filtered water. Often there were specialized bacteria living in these gills to help in the breakdown of the food as it was filtered in. The bacteria was ingested right along with the food particles. This strange-but-true situation is called a symbiotic relationship, where the two organisms depend on each other for sustenance. The bacteria seemed to get the short end of that stick!

While trilobites were prolific, they probably didn’t exactly rule the ancient seas. There must have been some predator who thought they would make a tasty lunch, but who could it have been? Perhaps it was the Orthoceras, a large cephalopod with reaching tentacles that surrounded their mouths. One fossil specimen indicates injury by the Anomalocaris, a large predator whose ring-like mouth probably could have swallowed a trilobite completely in a single gulp.No matter what the particular characteristic that inspires its popularity, this fossil will remain at the top of many collectors’ list. The wide range of availability makes it an affordable beginner’s piece as well as a boon to the paleontologist seeking to more deeply understand the nature of the ancient oceans in which the trilobite existed. For the avid collector there are some rare and unusual specimens to find. Perhaps it is simply that as one holds and turns this ancient creature, a time so long ago connects to the present and comes alive!

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