Hemiauchenia

Hemiauchenia; Temporal range: Mid Miocene-Late Pleistocene; ~10.3–0.012 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Fossil maxilla of Hemiauchenia cf. paradoxa
Scientific classification
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

Hemiauchenia,[1] synonym Tanupolama, is a genus of lamine camelids that evolved in North America in the Miocene period about 10 million years ago. This genus diversified and moved to South America in the Early Pleistocene, as part of the Great American Biotic Interchange, giving rise to modern lamines. The genus became extinct at the end of the Pleistocene.

Broad features of genus Hemiauchenia

The genus name is derived from the Ancient Greek: ἡμι- (hēmi-, "half"-)[2] and αὐχήν (auchēn, "neck").[3][nb 1] 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, 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.[5]

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.[6]

Distinguishing characteristics of members of Hemiauchenia

H. vera ( "true hemiauchenia")

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 ("Blancan hemiauchenia")

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 ("great-headed hemiauchenia")

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

H. minima ("least hemiauchenia")

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. According to 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.[7] 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.

Notes

These are used to form a feminine noun to mean "half-neckedness" or "half-carrying the neck"; cf. ὑψηλαυχενία, (hypsēlauchenía, "carrying the neck high").[4]

References

Paleobiology Database - Hemiauchenia basic info
ἡμι-. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
αὐχήν. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
ὑψηλαυχενία. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project
Ruez, D. R. (2005-09-30). "Earliest Record of Palaeolama (Mammalia, Camelidae) with Comments on "Palaeolama" guanajuatensis". Journal of Vertebrate Paleontology. Society of Vertebrate Paleontology. 25 (3): 741–744. doi:10.1671/0272-4634(2005)025[0741:eropmc]2.0.co;2. JSTOR 4524496.
Hemiauchenia at Fossilworks.org
"Hemiauchenia macrocephala". University of Florida, Florida Museum of Natural History. Retrieved 23 May 2016.