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 (, "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.

Distinguishing characteristics of members of Hemiauchenia

H. vera

H. blancoensis

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

H. minima

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.