Hemiauchenia

Hemiauchenia^[1] is a genus of lamine 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 three to two 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 (llamas and relatives) than to other Hemiauchenia species.^[2][3]

Hemiauchenia Temporal range: Mid Miocene – Late Pleistocene c. 10.3 – 0.012 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Reconstructed H. macrocephala skeleton, Florida Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	Camelidae
Tribe:	Lamini
Genus:	†Hemiauchenia Gervais & Ameghino, 1880
Species
H. macrocephala (Cope, 1893) H. minima (Leidy, 1886) H. blancoensis (Meade,1945) H. vera (Matthew, 1909) H. paradoxa (Gervais & Ameghino, 1880) H. seymourensis H. edensis H. guanajuatensis H. mirim Greco et al., 2022
Synonyms
Tanupolama Stock 1928 Holomeniscus Cope 1884

This genus gave rise to the genus Lama, of which modern lamines belong to.

Broad features of genus Hemiauchenia

The genus name is derived from the Ancient Greek: ἡμι- (hēmi-, "half"-)^[4] and αὐχήν (auchēn, "neck").^{[5][nb 1]} Species are specified using Latin adjectives or Latinised names from other languages.

North American fossils

Restoration of Hemiauchenia (right) and other animals of the Rattlesnake Formation fleeing a volcanic eruption

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.^[7][8]

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.^[9]

H. macrocephala gave rise to modern lamines (guanacos, vicuñas, and their domesticated forms) when a population migrated southward towards South America.^[10][11][12]

South American fossils

Fossil skull of the type species, H. paradoxa

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.^[13] Hemiauchenia paradoxa is suggested to have been a browser.^[14]

Distinguishing characteristics of members of Hemiauchenia

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

Skull of H. macrocephala

• 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

Thought to have been browsers^[15] and mixed feeders.^[16] Suggested to be less closely related to modern Lama and Vicugna than H. paradoxa is.^[3]

Native to the southern United States, spanning from California to Florida,^[17] and as far north as Nebraska.^[16] Also present in Mexico.^[15]

H. minima

Right hind limb of H. minima, Florida Museum of Natural History

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

Other species

Toe bone of H. edensis, Florida Museum of Natural History

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.^{[citation needed]}

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.^[18] 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.^[2]

Diet

Over the Pliocene and Pleistocene, Hemiauchenia was an intermediate feeder that preferred browsing with a hypsodont dentition.^[19] 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.^[20]

See also

• Paleontology portal
• Prehistoric mammals portal

Notes

1. These are used to form a feminine noun to mean "half-neckedness" or "half-carrying the neck"; cf. ὑψηλαυχενία, (hypsēlauchenía, "carrying the neck high").^[6]