Top Left: Llama - Lama glama
Top Right: Vicugna - Lama guanicoe
Center: Alpaca - Vicugna pacos (previously categorized in genus Lama)
Bottom: Bactrian camel - Camelus bactrianus
The Camelids are Artiodactyla (even-toed ungulates) that first evolved in North America during the Eocene epoch (55.8 MYA - 33.9 MYA). Like horses, this group of animals evolved here for millions of years, but went extinct in North America after populations crossed the Bering land bridge.
Unlike horses, however, the Camelids not only crossed over into Asia, but they also went south, into South America, during the Great American Exchange.
The camelids which moved south evolved into what we now know as the tribe Lamini - the llama and guanaco (genus Lama), and alpaca and vicugna (genus Vicugna). The camelids which traveled into Asia, the Middle East, and North Africa, evolved into the tribe Camelini - the Bactrian and dromedary camels (genus Camelus).
The Animal Kingdom, based on the writings of Eminent Naturalists: Vol 2. Hugh Craig, 1902.