The Middle Jurassic period, roughly 170 million years ago, saw a time when tropical waters made their mark on what is now central England. Shallow, clear seas spread over the region, depositing layers of shell and coral sand, like that of the present-day Bahamas. These sedimentary deposits now form the Cotswold limestones, giving rise to the Cotswold Hills which just impinge on the southernmost parts of Warwickshire.
This sea supported a diversity of marine life, ranging from sea-urchins, to corals, to clams and sea-snails. Some of these were very similar to those of modern tropical and sub-tropical seas; others became extinct millions of years ago.
Amongst the extinct sea-snails, there are the bizarre ‘nerineoids’; a group that flourished in tropical waters during the Jurassic Period between about 200 and 140 million years ago. The outside of their shells tends to look quite normal, but internally their spiral shells bear interesting folds which are beautifully revealed when the fossils are sliced down the middle, as in the photo on the page, or by following this link. Today, these fossils typify Jurassic deposits at lower latitudes, such as the Jurassic limestones of southern Europe. In Britain, they invaded the Middle Jurassic seas, whose favourable, warm and clear conditions allowed them to briefly flourish.
Today, these tropical invaders can still be found in the Cotswold limestones of southernmost Warwickshire and surrounding areas of the North Cotswolds. Warwickshire Museum’s collections also include representative examples – silent witnesses to a warmer world in our distant geological past. One of these is shown in the photograph on this page.