From shrews that walked with dinosaurs…
The mammal fossils in our collections include huge tusks, teeth and bones of elephants and hippos. Most date back to the Ice Age, but mammals did exist millions of years before this, beginning with tiny shrew-like creatures that lived at the time of the dinosaurs.
Hippos and hyenas in Honiton!
The Ice Age started about two million years ago but within it there have been many warm periods or ‘interglacials’. Most of our mammal fossils date back to one of these interglacial periods, about 125,000 years ago. During this time, it was so warm in Britain that elephants, hippos and hyenas wandered along the banks of the River Otter, in the place we now call Honiton.
The first mammals include shrew-like creatures that lived over 150 million years ago, when dinosaurs first walked the earth. Their fossils have been found within a layer of rocks around Swanage called the Purbeck Beds. Much has happened since the arrival of those tiny mammals. Dinosaurs became extinct, allowing mammals to explode into the myriad of forms we see today. Spectacular animals such as the giant sloth and woolly mammoth appeared – then disappeared forever.
Boiling for bones
Along the Jurassic Coast there are only two locations where mammal fossils have been found – Watton Cliff, near West Bay and the Purbeck Beds, Swanage. Usually all that remains are teeth and scattered bones. These fossils are recovered by collecting mud, boiling and sieving it, then searching through the fine residue with a microscope.
Our ancient ancestors
Mammals evolved from ‘synapsids’. This group of creatures is characterised by having a single opening in the skull behind the eye. The opening, called the ‘temporal fenestra’ or ‘window in the skull’, provided space for the muscles that worked the jaws. Find out more on the reptiles and amphibians page.
Mammals and reptiles go separate ways
The evolutionary split between mammals and reptiles took place during the Jurassic period. As mammals evolved, the hole in their skull became closed, whereas crocodiles, ichthyosaurs, plesiosaurs and dinosaurs have two openings in the skull.
But the simplest way to tell the difference between mammals and reptiles is in the teeth. Mammals’ teeth evolved into canines, incisors and molars, each serving a different function. But reptiles retained their rows of identical or similarly-shaped teeth.
The other remarkable adaptation was in the evolution of mammals’ ears, which allowed far more sensitive hearing.