Camelids are even-toed ungulates classified in the order Artiodactyla, along with species including whales, pigs, deer, cattle, and antelopes.

As in ruminants, the upper incisors are largely absent and are replaced by a dental pad consisting of connective tissue covered with epithelium.

[1] They have three-chambered stomachs, rather than four-chambered ones; their upper lips are split in two, with each part separately mobile; and, uniquely among mammals, their red blood cells are elliptical.

Camelids first appeared very early in the evolution of the even-toed ungulates, around 50 to 40 million years ago during the middle Eocene,[citation needed] in present-day North America.

By the late Eocene, around 35 million years ago, camelids such as Poebrotherium had lost the two lateral toes, and were about the size of a modern goat.

[6][11] The family diversified and prospered, with the two living tribes, the Camelini and Lamini, diverging in the late early Miocene, about 17 million years ago, but remained restricted to North America until about 6 million years ago, when Paracamelus crossed the Bering land bridge into Eurasia, giving rise to the modern camels, and about 3-2 million years ago, when Hemiauchenia emigrated into South America (as part of the Great American Interchange), giving rise to the modern llamas.

[citation needed] A population of Paracamelus continued living in North America and evolved into the high arctic camel, which survived until the middle Pleistocene.

Finally, a number of very tall, giraffe-like camelids were adapted to feeding on leaves from high trees, including such genera as Aepycamelus and Oxydactylus.