Welcome to Vincent’s Cabinet of Curiosities. A fossil is simply the remains of a prehistoric plant or animal, usually preserved in rock. The word derives from the Latin ‘fossilis’, meaning something dug up and their study is called palaeontology. People have been aware of them and their origin hotly debated for centuries. For example, Leonardo da Vinci (1452-1519) was fascinated by them. Most consist of the hard parts of the once living organism, for instance shells, bones and teeth. In a sense they are a ‘back-stage pass’ into the distant past, showcasing the complex succession of plant and animal species that once inhabited this wondrous planet of ours.
I was 10 years old when I found my first fossil, a single shelled mollusc or gastropod, embedded in a piece of Carboniferous limestone which formed on the bed of a sub-tropical sea some 340 million years ago. This is a light grey coloured rock which is readily apparent from the photo. A pivotally important moment in my life, it marked both the beginning of my collecting and my lifelong fascination with limestone! I initially mistook it for an ammonite because of the similar spiral shape. These are however quite different marine invertebrates.
Ammonites belong to a group of molluscs known as cephalopods and are related to present day octopus, squid and cuttlefish. They derive their name from the spiral form reminiscent of the ram horns sometimes depicted on the head of the Egyptian God Ammon. They were well established in the primeval sea by around 380 million years ago. Their hard outer shells were composed of a substance called aragonite and were divided internally into a series of separate chambers. The animal occupied the outer one and as it grew added on a new section toward the front into which it moved, sealing off the back with a thin wall or septa. The disused chambers were filled with a mixture of water and gas, the portions of which could be adjusted by means of a hollow, connecting tube called a siphuncle. This allowed the animal to move up and down in the water column as its buoyancy was changed. The term cephalopod is derived from the Greek meaning ‘head-footed’ and refers to the arrangement of tentacles that radiated from its head. These were used to seize and hold prey which consisted of crustaceans and fish. Now completely extinct as a group, they varied greatly in size with some species growing to over 6 feet in diameter. In 2001 I found a pebble on a beach in Whitby on the Yorkshire coast, a place famous for its Jurassic Period fossils. I cracked it open to reveal the ammonite in the photo. Called Dactylioceras, that was the first time in 185 million years that the sun had shone on it! Known locally as ‘snake-stones’, it was believed at one time that they were snakes petrified by St. Hilda, a personage associated with the town.
The chambered nautilus is the sole living relative of the ammonites. A nocturnal creature by habit, it is found in the Pacific down to depths of 1,800 feet. It possesses a hard beak-like appendage which it uses when feeding. The shell of an adult animal is around 6 inches across and is whitish in colour streaked with reddish serrated stripes to help camouflage it. The specimen I am holding was gifted to me when I was fifteen by my sister Barbara for my collection. I have included photos of a cross-section of an ammonite and a nautilus to show the internal chamber structure of their shells and a model of an ammonite for comparison with a nautilus.
The bullet-shaped object is the tail section of the internal shell of a squid-like cephalopod called a belemnite and was probably used for balance when the creature was swimming. Known as a rostrum, it is composed of calcite, the crystalline form of calcium carbonate. In the past they were named ‘thunderbolts’ based on a belief that they were darts thrown down to earth from the heavens during thunderstorms. The specimen in the photo is around 180 million years old.
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