Although they were often compared by early writers to sheep and spoken of as such, their affinity to the camel was very soon perceived. They were included in the genus Camelus in the Systema Naturae of Linnaeus. They were, however, separated by Cuvier in 1800 under the name of Lama along with the alpaca and the guanaco. Vicuñas are in genus Vicugna. The animals of the genus Lama are, with the two species of true camels, the sole existing representatives of a very distinct section of the "Artiodactyla" or even-toed ungulates, called Tylopoda, or "bump-footed," from the peculiar bumps on the soles of their feet, on which they tread. This section thus consists of a single family, the Camelidae, the other sections of the same great division being the Suina or pigs, the Tragulina or chevrotains, and the Pecora or true ruminants, to each of which the Tylopoda have more or less affinity, standing in some respects in a central position between them, borrowing as it were some characters from each, but in others showing great special modifications not found in any of the other sections.

The discoveries of a vast and previously unsuspected extinct fauna of the American continent of the Tertiary period, as interpreted by the palaeontologists Leidy, Cope, and Marsh, has thrown a flood of light upon the early history of this family, and upon its relations to other mammals.

It is now known that llamas at one time were not confined to the part of the continent south of the Isthmus of Panama, as at the present day, for their remains have been abundantly found in the Pleistocene deposits of the region of the Rocky Mountains, and in Central America, some attaining a much larger size than those now existing. Some species of llamas did stay in North America during the last ice ages. 25,000 years ago, llamas would have been a common sight in modern-day California, Texas, New Mexico, Utah, Missouri, and Florida. These North American llamas belong to a single genera, Hemiauchenia, which is extinct.

Many camel-like animals exhibiting different genetic modifications and a gradual series of changes, coinciding with the antiquity of the deposits in which they are found, have been traced from the thoroughly differentiated species of the modern epoch down through the Pliocene to the early Miocene beds. Their characters having become more generalized, they have lost all that especially distinguishes them as Camelidae: they are merged into forms common to the ancestral type of all the other sections of the Artiodactyles.

Hitherto none of these annectant forms have been found in any of the fossiliferous strata of the Old World; it may therefore be fairly surmised (according to the evidence at present before us) that the Americas were the original home of the Tylopoda, and that the true camels have passed over into the Old World, probably by way of north Asia. Gradually driven southward, perhaps by changes of climate, and having become isolated, they have undergone further special modifications. Meanwhile, those members of the family that remained in their original birthplace have become, through causes not clearly understood, restricted solely to the southern or most distant part of the continent. There are few groups of mammals for which the palaeontological history has been so satisfactorily demonstrated as the llama.