Eocene (Pt 4): Ancient Beasts of the European Archipelago

Propalaeotherium

The story of the evolution of the horse is one of the most commonly cited examples of evolutionary trends, often illustrated by a series of increasingly horse-like animals with an ever-reducing number of toes. The animal typically shown at the start of that series is, depending partly on the age of the picture, either Hyracotherium or Eohippus.

Hyracotherium was long regarded as the earliest known member of the horse family. In recent decades, it has become apparent that it wasn't really a horse, in the sense that modern horses don't descend from it or its relatives, and today we call the family it belonged to the palaeotheres. The North American Eohippus, on the other hand, despite long being thought to be identical to Hyracotherium, probably is a horse. The confusion between the two means that it's often difficult to tell which is being referred to in older sources.