The fossils of Stonesfield

A Spotlight Specimens special for Oxford Festival of Nature

By Eliza Howlett, Earth Collections manager

There was a time, more than 160 million years ago, when most of Oxfordshire was covered by a warm, clear, shallow sea. Offshore, the waters were agitated by waves and storms, but closer to land these forces were buffered by a submerged sandbank, and calm lagoons developed.

The area that is now Stonesfield was part of this lagoonal environment, and the fossils that have been found there provide a wonderful window into the living world of this Middle Jurassic sea.

So how would these sea creatures compare with British marine life today? Some things would have been very familiar. On the sea bed you would have found a huge variety of bivalves, or clams, along with lobsters, crabs and sea urchins; the waters above would have been full of fish, including several different types of shark.

But there would have been other things too: squid-like belemnites, and nautiloids and ammonites with coiled shells, and tentacles like an octopus. Instead of dolphins and porpoises there would have been sea crocodiles and sea turtles, and in the skies above, flying reptiles known as pterosaurs rather than the usual sea birds.

And there’s more. Stonesfield fossils also include plants and animals washed in from nearby land: the leaves and seeds of conifers and cycads, beetle wing cases, reptile eggs, and the remains of both dinosaurs and mammals.

One particularly spectacular find was the lower jaw of the carnivorous dinosaur Megalosaurus, nine metres long in life and weighing about a tonne. Megalosaurus became the first creature to be named a ‘dinosaur’, in 1824. Less obvious, but equally significant, are the tiny jaws of some of the shrew-like mammals that would have lived alongside the dinosaurs: Phascolotherium, Amphitherium, Amphilestes and Stereognathus – the first Jurassic mammals known to science.

Along with the preservation of delicate items such as dragonfly wings and the leg of a cricket, and the original colour patterns on some sea snails, limpets and barnacles, the fossil material from Stonesfield is really quite special.