A common find in some gardens are fossils, mostly of shelled sea creatures. Courtesy, I assume, of the worms, they turn up on the soil surface. Many are conglomerations, a fused mass of differing species which are hard to tell apart but others are quite clean and can be identified.
Finding fossils at a height of approximately 225m above sea level seems odd when you first think about it, especially when the area is about as far from the sea as you can get on this island.
How did they get there? Here I turned to geology for answers. At the time these fossils were living, some 170 million years ago, the layout of the continents was very different, much of Europe was under a warm and shallow sea and Britain was farther south than it is now. It was only when the single great continent that was once Pangaea split apart that we begin to see anything recognisable as the planet we live on today.
The fossils I’m looking at today lived, I think, during the middle Jurassic era called the Mesozoic. They are a sea urchin (echinoid) and clams (bivalves or brachiopods). The bivalves interest me – they attached themselves to a surface under water by a stem called a pedicle and thereafter lived their lives in that one place.
Showing how they attached themselves to a surface
Which leads me to the next thing – a curious thing about bivalves from this era is how unsymmetrical and plain lop-sided they can be compared to many we see today. The ‘why’ and ‘how’ of it prompts me to ask a question that the class was asked often when I was studying horticulture – ‘What is the advantage of this adaptation?’. It’s a good question and one to be asked often. In this case, my guess is that these ancient shelled creatures evolved to take advantage of the water current and the food it carried, their shells formed so as to move to and fro smoothly as the water flowed past them.
Alongside them lived sea urchins (echinoids), which differ from the bivalves in that they can move around to hunt their food. The piece of echinoid I found was lying on the soil surface and I believe it is called Clypeus ploti.
I found a little about it in a pdf about the geology of the Cotswolds:
‘This particular species of echinoid lends its name to the uppermost beds of the Inferior Oolite Group (the Clypeus Grit) and has been known locally by various names such as “Chedworth Buns”, “Poundstones” or “Fairy Loaves”. Superstition said that keeping one in your house meant that you would never run out of bread and were protected from witchcraft. They were described by Sir Thomas Plot in the 17th century and in reality are fossilised sea-urchins from the Middle Jurassic and would have lived in the warm, shallow tropical seas at that time’.
I suppose having part of a Chedworth Bun means we may always have a crust to chew on and, given the nature of the soil in this area – pinkish-brown clay full of rubble – we shall need it. Being protected from witchcraft would also be handy.
You could easily keep drilling down through all this material and study it for the rest of your life. I often wish I had the time necessary in order to find out about all the things that interest me, but there are just too many of them, and finding out one thing so often leads to half a dozen other intriguing subjects. With the time I do have, I skim the surface to try and gain a rough awareness, to be added to the ever-growing net of events and species that make up the natural history of this remarkable planet. All this started by looking at the ground beneath my feet.
The book I turned to in attempting to identify these fossils, as well as others, is one of a series on British fossils by the Natural History Museum called ‘British Fossils – Mesozoic‘. They are very useful books with beautifully clear illustrations and it’s worth having them all on the shelf. The Mesozoic is described by the Wiki page as ‘an interval of geological time from about 252 to 66 million years ago. It is also called the Age of Reptiles. The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs and stages’.