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Evolution And Present Situation Of The South American Ccamelidae

The South American camelids are classified together with the Old World camels in the order Artiodactyla, suborder Tylopoda, and family Camelidae, but subdivided into Lamini and Camelini at the tribe level.  Two New World genera, Lama and Vicugna, and one Old World genus, Camelus, are recognized.  Ruminant digestion in the Tylopoda evolved independently of, and parallel to, ruminant digestion in the suborder Pecora (Bohlken, 1960).  The Camelidae are distinguished by: absence of horns or antlers, presence of true canines separated from the premolars by a diastema in both the upper and lower jaws, position of the vertebral artery confluent to the neural canal in the cervical vertebrae, anatomy of the rear limbs which permits the animal to bend its legs beneath the body and rest on its stomach, and the presence of a nail covered digital pad rather than a hoof.

In 1758, Linnaeus described the two domestic New World camelids as Camelus lama "Camelus peruvianus Glama dictus" (llama) and Camelus pacos "Camelus peruvianus laniger Pacos dictus" (alpaca), placing them together in a single genus with the Old World dromedary and bactrian camels, Camelus dromedarius and Camelus bactrianus.  The two remaining New World species, the wild guanaco and vicuña, were subsequently designated Camelus guanicoe by Miiller in 1776 and Camelus vicuña by Molina in 1782.  As early as 1775, Frisch proposed that the four New World species be placed in the genus Lama, but this work is not accepted by the International Commission on Zoological Nomenclature (Hemming, 1985a) and authorship of Lama is credited to Cuvier, 1800 (Hemming, 1958b).  According to the accepted nomenclature as listed in Cabrera (1961), the vicuña was assigned to a separate genus, VicuLna, in 1872 by Gray.  None the less, the citation of Gray, 1872 is in error as this author described the vicufia as Llama vicugna (1872: 1 0 1).  The earliest reference to Vicugna is by Miller, who in 1924 proposed the generic separation based upon the vicufia's unique hypselodont incisors. 

Although this designation has not been universally recognized, recent molecular analysis based on mtDNA sequence data suggests that classification into two genera could be appropriate (Stanley, Kadwell & Wheeler, 1994).  Four species of New World camelids survive today: the llama, L. glama (Linnaeus, 1758), alpaca L. pacos (Linnaeus, 1758), guanaco L. guanicoe (Mijller, 1776) and vicuna VicuL'na vicugna (Molina, 1782)(Figure 1); together with the Old World domestic dromedary Camelus dromedarius Linnaeus, 1758 and domestic and wild Bactrian camels C. bactrianus Linnaeus, 1758.

The tribe Larnini, represented by fossils of the genus Pliauchenia, originated in the Great Plains of western North America between 9 and I I million years ago (Myr)(Harrison, 1985) (Figure 2).  Two genera, Alfori as (I 0-4.5 Myr)(Harrison, 1979) and Hemiauchenia (I 0-0.  I Myr)(Webb, 1965, 1974) evolved from Pliauchenia approximately 10 Myr.  The first of these, Alforjas, and its descendant CamelWs (4.5-0.1 Myr) remained in North America (Harrison, 1979; Webb, 1965, 1974), while some species of Hemiauchenia migrated to South America during the Pliocene/Pleistocene transition approximately 3 Myr.  It is from the latter genus that Lama and VicuLyna evolved in South America approximately 2 Myr (L6pez Aranguren, 1930; Cabrera, 1932; Webb, 1972; Harrison, 1985).  Palaeolama (1.5-0.1 Myr), the other descendant of Hemiauchena, is no longer considered to be an ancestor of Lama and Vicugna.  Only Lama and Vicugna survived the end of the Pleistocene period some 10,000 years ago.

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