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Molting
As with modern day arthropods, trilobites occasionally shed their exoskeleton (molted). During early stages in the trilobite's life cycle, molting often increased the amount of the animals thoracic segments as well as it's size, although unlike butterflies, the general form stayed relatively unchanged. Exoskeletons shed while the trilobite was still alive had the opportunity of being fossilized similar to the animal itself, hence, a fair share of trilobite fossils in collections today are actually fossilized molts. Additionally, recent research on trilobite mass burial sites suggests that some species may have simultaneously molted together as a group. Although a final conclusion as to why this happened may never be found, it is speculated that trilobite mating behavior took place when in their soft-shelled form during molting.
Tracks and Trails
In addition to having the fossilized remains of trilobites and their molts, the tracks and trails they made while living in their environments were also sometimes preserved. Although it's hard to find direct evidence of mobility markings with the associated organism that made them (i.e., fossilized trilobites next to their trails), a few intact trilobite specimens have surprisingly been found near preserved sediment markings. Studies have been conducted on what probable markings would look like from trilobite limbs, and based on the finds of this research , a wide variety of markings have been identified to be from trilobites, which include walking tracks, burrows, feeding trails and resting locations. These fossiled tracks and trails help to shed important light on the life activities of trilobites.
Extinction
Trilobites were extremely successful animals for some 521 million years of Earth history. From their yet unknown earliest ancestors in the Cambrian or PreCambrian, to the first fossilized specimens from the Lower Cambrian, through their radiation and diversification in the Middle Paleozoic, to their eventual decline and extinction at the end of the Permian, they continue to excite the imaginations of amateur geologists as well as professional scientists worldwide. Most of us have at least a few trilobite specimens in our collections, with more on the way in the future. Hopefully this brief review on the world of trilobites helps shed some light on these important creatures from the past.
Trilobite Tracks - Bisher Formation, Lower Silurian,
Adams County, Ohio
Morphology: The study of the form of living organisms including plants and animals, and the relationship between their structures.
Ecological Niche: Term referring to an environment, and the role and interactions that an organism has within it, both with the biotic (living) elements also inhabiting the same environment as well as the abiotic (physical) factors. Includes the abundance of food, shelter, how an organism survives and reproduces, deals with competitors, life history, place in the food chain and other conditions.
Definitions
Phacops sp. - Devonian, Morocco