Hemiauchenia

Hemiauchenia is a genus of laminoid camelids that evolved in North America in the Miocene period about 10 million years ago. This genus diversified and entered South America in the Late Pliocene about 3-2 million years ago, as part of the Great American Biotic Interchange. The genus became extinct at the end of the Pleistocene. The monophyly of the genus has been considered questionable, with phylogenetic analyses finding the genus to paraphyletic or polyphyletic, with some species suggested to be more closely related to living lamines than to other Hemiaucenia species.

Broad features of genus Hemiauchenia
The genus name is derived from the ἡμι- (, "half"-) and αὐχήν (, "neck"). Species are specified using Latin adjectives or Latinised names from other languages.

North American fossils
Remains of these species have been found in assorted locations around North America, including Florida, Texas, Kansas, Nebraska, Arizona, Mexico, California, Oklahoma, New Mexico, Oregon, Colorado, and Washington. The "large-headed llama", H. macrocephala, was widely distributed in North and Central America, with H. vera being known from the western United States and northern Mexico. H. minima has been found in Florida, and H. guanajuatensis in Mexico.

South American fossils
Fossils of Hemiauchenia in South America are restricted to the Pleistocene and have been found in the Luján and Agua Blanca Formations of Buenos Aires Province and Córdoba Province, Argentina, the Tarija Formation of Bolivia, Pilauco of Osorno, Los Lagos, Chile and Paraíba, Ceará, and the Touro Passo Formation of Rio Grande do Sul, Brazil. Hemiauchenia paradoxa is suggested to have been a browser.

H. vera

 * Relatively low-crowned teeth (part of visible teeth ends close to gums)
 * Large caniniform (canine-like) upper first premolar
 * Retention of lower third premolar

H. blancoensis

 * Named for Blancan Age stratum where typically found
 * Shorter mandibular diastema (teeth-spacing between incisors and molars) than H. macrocephala and H. vera
 * Caniniform upper first premolar
 * Absent second premolar
 * Upper third premolar present or absent
 * Lower crowned molars

H. macrocephala
Thought to have been browsers and mixed feeders. Suggested to be less closely related to modern Lama and Vicugna than H. paradoxa is.
 * Possesses a larger skull relative to other species
 * Long, robust limbs
 * Large skeletal size
 * Presence of a deciduous upper second premolar
 * Fully molariform deciduous second premolar (its infant bicuspids were like molars)
 * High-crowned molars
 * Thick layer of cementum on the teeth
 * Broad mandibular symphysis (line where the bones of the jaw join together) with incisors in a vertical fashion

Native to the southern United States, spanning from California to Florida, and as far north as Nebraska. Also present in Mexico.

H. minima

 * Despite being the earliest recognized species, general distinguishing characteristics for H. minima are little known.

Other species
Also, a few lesser known species, such as H. paradoxa, H. seymourensis, H. edensis and H. guanajuatensis, have been found. Depending on which source is consulted, these may or may not be considered legitimate taxa.

Classification history
Prior to 1974, fossil specimens now thought to be Hemiauchenia were classified as Holomeniscus, Lama, and Tanupolama, until S. David Webb proposed that these North and South American fossil species were part of a single genus. This has been accepted by all subsequent researchers, although in 2013, Carolina Saldanha Scherer questioned the inclusion of a certain North American species and suggested that Hemiauchenia is paraphyletic.

Diet
Over the Pliocene and Pleistocene, Hemiauchenia was an intermediate feeder that preferred browsing with a hypsodont dentition. According to δ13C analyses of H. paradoxa teeth from the Touro Passo and Santa Vitória Formations of Brazil, H. paradoxa was primarily a grazer of C3 grasses.