This is part of the fossilised lower jaw of a Straight-tusked elephant. It has one of the molar teeth still in its socket. It was found on East Mersea along with another molar tooth, a fragment of tusk and part of a limb bone.
Straight-tusked elephants are one of the largest land mammals that has ever lived. They roamed Europe in the Pleistocene period, becoming extinct in Britain about 115,000 years ago. Unlike their distant cousin the Woolly mammoth, who lived on the icy tundra, the Straight-tusked elephant lived in wooded areas and preferred the relative warmer conditions of the interglacial periods of the last Ice Age, only reaching Britain in warmer periods.