The earliest known camel, called "Protylopus", lived in North America 40 to 50 million years ago (during the Eocene). It was about the size of a rabbit and lived in the open woodlands of what is now South Dakota. By 35 million years ago, the "Poebrotherium" was the size of a goat and had many more traits similar to camels and llamas. The hoofed "Stenomylus", which walked on the tips of its toes, also existed around this time, and the long-necked "Aepycamelus" evolved in the Miocene.