Brachiopods (lamp shells) are by far the most common fossils at Arisaig. Like bivalves, they have two shells but the shells are not the same shape. There have been brachiopods in Earth's oceans for more than 400 million years. Today, however, only a few types remain.

Bivalves, such as clams are familiar creatures. The two halves of a clam shell are virtually identical - this is how you can tell them from brachiopods. In the Silurian sea, bivalves were not nearly as common as brachiopods. Look for them as impressions in the rock.

Gastropods from the Silurian sea look generally like modern snails, but some are quite strange. One form had a coiled shell that flared at the bottom, perhaps an adaptation to walking on soft mud. At Arisaig, the best gastropods are found in the limestones.

Nautiloids, or horn shells, were predators closely related to modern day squid. They had a cone-shaped shell with chambers inside. The chambers held air to provide buoyancy so the nautiloid could swim. Some large nautiloid shells up to 30 centimetres (12 inches) long have been found at Arisaig. People once thought that these were the horns of the mythical unicorn. Look for tapered shells with chambers inside to identify them.

Trilobites are an extinct group of arthropods. Modern arthropods are creatures such as insects and crabs, with hard external skeletons and jointed legs. Trilobites had large compound eyes like modern insects and scurried along the sea floor. Usually only broken pieces of trilobites are found at Arisaig, but watch for whole ones or head sections.

Graptolites are extinct also, and nothing exactly like them lives today. Imagine a colony of creatures living in small chambers along something that looks like a tiny hacksaw blade. Gas-filled floats supported the colony. Graptolites had no hard body parts; the long thin colonies are preserved as shiny black carbon film on the rock.

Crinoids, also known as sea lilies, are not plants at all. They are filter-feeding animals that live attached to the sea bottom by a thin stalk. At the top of the stem is a plate-covered body with ten or more feathery tentacles that collect food. Several kinds of crinoids still live today. Whole crinoids are not often fossilised because, unless they were buried quickly and gently by mud soon after death, the plates come apart and scatter. You will probably find sections of stem - they look like stacks of small coins with a star shape in the centre.

Bryozoans, or moss animals, lived as colonies of individuals in a hard, shell-like skeleton. At Arisaig, there are branching, stick-like forms (stony bryozoans) and also encrusting forms (lacy bryozoans). The surface of the bryozoan is covered by tiny pits that once contained the individual soft-bodied creatures. These pits are a good clue for identifying a bryozoan fossil. Bryozoans still live today.

Tentaculites and cornulites are commonly found at Arisaig. We are not exactly sure what sorts of creatures produced these small cone-shaped fossil shells with rings.

Interpreting Arisaig's Fossils	Important Sites Home	Final Note