Propalaeotherium

Two species of Propalaeotherium, tiny forest-living horses are known from Eocene sites in Germany. The fossils have preserved an exact body outline.

Even the stomach contents of Propalaeotherium were preserved, so we know exactly what they ate. Preservation was so good that when leaves from their stomachs were put under a microscope and shown to a botanist, they couldn't tell that the leaves were 50 million years old.

Traits & Evidence
The Propalaeotherium shown in program one are reconstructed from fossils found in Germany. Two species are found in the Messel shales, and other early horses are found in North America and throughout Europe. The remarkable fossils have preserved an exact body outline, allowing us to reconstruct them very accurately. One of the fossils even showed a pregnant mare with a foal inside.

Amazingly, some of the fossil Propalaeotherium are so well preserved that we can see their stomach contents and so we know exactly what they ate. In fact when some of the leaves found in their stomachs were put under a microscope and shown to a botanist they couldn't tell that the leaves were 50 million years old as they were so well preserved. These are mostly leaves picked up from the forest floor. One specimen, though, had been gorging itself on fallen grapes - the same kind as we make wine from (Vitis species). Obviously a vine had been fruiting and dropping grapes onto the forest floor just before this animal died.

All the early mammals around this time (50 million years ago) were small - the largest being about the size of a pig. This is because the World was covered in thick tropical forest - there simply wasn't room to get big! Being small and nimble, the little horses could browse the fallen fruit and leaves, and make quick dodges into the undergrowth to hide from predators such as Gastornis.

Appearance
Just about the only information we were missing to recreate Propalaeotherium for the program was its natural colours. Some of the fossil beetles from the same place are coloured, but this is because their colour is caused by the very fine structure of their shells diffracting the light. This structure can be preserved by such exquisite fossilisation (although their colours may change slightly). However, most mammals use pigment molecules in their skin and hair to create their colours, and these molecules degrade as the body decays. So, to design a colour scheme for the animals we looked at that of small forest deer, which live in a similar habitat. They need to avoid predators, and in the dappled forest light, dark brown with paler spots seemed to be the most common colours for camouflage.

The early horses were quite similar to their relatives the tapirs (which have changed little in the last 50 million years), and had feet with several nail-like hooflets. These gave them a good grip for fast acceleration into undergrowth on the forest floor. Modern horses have only one toe on the ground, whose nail has expanded into a hoof to bear the weight. These single toes are designed for speed over a long distance on the plains.