Trilobites

Trilobites are found as extinct fossils of the phylum Arthropoda and class Trilobita. They were the most numerous and successful marine organisms of the early Paleozoic. These segmented, "pill-bug" - like athropods ranged in length from several millimetres to 3 feet. They had many legs, each with a set of gills, and most had sophisticated, multifaceted eyes. Like most arthropods, trilobites could grow only by shedding their old skins. Consequently, many of the trilobite fossils that are found are actually shed external skeletons and not the trilobite animals themselves.

This trilobite was bought at the Fossil Shop, Lyme Regis, Dorset - but originates from Morocco

The name "trilobite" is derived from the three lobes into which each body segment is divided - two lateral pleural lobes and an axial lobe. Most trilobites lived in shallow ocean waters and on reefs. It has been proposed, however, that some of the spiny trilobites may have been cabable of swimming. Trilobites are relatively common in Cambrian, Ordovician, and Silurian rocks throughout the world. By the Devonian, they had declined to the point of being relatively rare finds. In the late Carboniferous and Permian, they are extremely rare. They are most likely to be found in limestones and shales.

When preserved in shales, trilobites are usually flattened, and often the original shell has been destroyed, leaving only an extrenal cast. In some shales, however, entire skeletons are preserved in excellent detail. Specimens in limestone are frequently preserved in three dimensions, with the skeletal material intact. Trilobites were gregarious animals and are frequently found in large numbers, wither in deposits from storm activities or on bedding surfaces. It is not unusual for them to be locally abundant in Cambrian and Ordovician rocks as deposits or debris left by storms. It is also not unusual to find enrolled trilobites, curled up upon themselves, apparently a defensive behaviour.

(The Nature Company Guides: Rocks & Fossils)


This little tiny fellow (much enlarged) is Bettonolithus chamberlaini Ordovician, Llanvim Series, Gilweem Hill near Hundred House, Powys, Mid Wales

A Guide To The Order Of Trilobites