Fossils

Crinoids

Crinoids, also known as sea lilies or feather stars can still be found in the oceans today, however were much more abundant in the geological past. When alive crinoids are essentially characterised by having a mouth at the top of a long stem, which is surround by five feeding arms.

Once the crinoids dies the delicate feeding arms usually get destroyed and the stem, which is made up of a series of hard, calcareous "polo" shaped disc, disarticulate (i.e. break apart) and are deposited in the sediment. These are called crinoids ossicles.
 

 

Occasionally, exceptionally well preserved fossils are found which give a complete picture of how these extinct forms of crinoids would have looks.

Brachiopods

Brachiopods are a hard shelled marine animal with an upper and lower "valve" (shell). Most species of brachiopods went extinct in the Permian-Triassic mass extinction, but many forms still survive today. Brachiopods generally have "valves" of different sizes and they have a straight hinge line (where the lower and upper valves join). In life they are attached to the substrate (sediment, rock etc) by a fleshy protrusion known as a pedicle. From a fixed position on the sea floor brachiopods open their shells and filter feed on plankton. Brachiopods are mostly found in fairly high energy environments with fairly strong currents. The shells of brachiopods are made from a mineral called calcite (a form of calcium carbonate).

 

 

Corals

Two main types of corals are evident in the rocks used in the instrument, solitary and colonial corals. Solitary corals from the order Rugosa are the most common found in many of the limestones. They are called solitary corals because they contain just one polyp (the living part of a coral). They also have quite a distinctive horn-like shape viewed from the side and have a rounded cross section with a radial pattern of fine structures called septae.
 

 

The type of colonial corals that might be seen in some of the limestones are known as tabulate corals. These are essentially a mass of individual hexagonal cells, known as corallites, each containing a one polyp. The cells form a network that gives the coral a honeycomb appearance.

Belemnites

Belemnites are an extinct form of cephalopods, similar to modern day squids and closely related to cuttlefish. The only parts of belemnites that survive fossilised are the rostrums or guards. This is hard, mineralised (calcite) part of the animal was used to give the belemnite neutral buoyancy and aid stability within the water.
 

 

All images sourced from Wikipedia Commons