''Teleoceras'' (Greek: "perfect" (teleos), "horn" (keratos)) is an
extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
rhinocerotid
A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...
. It lived in
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
during the
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
and
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58epochs during the
Hemingfordian
The Hemingfordian on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 20,600,000 to 16,300,000 years BP. It is usually considered to overlap the lates ...
to the end of
Hemphillian
The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered t ...
from around 17.5 to 4.9 million years ago. It grew up to lengths of long.
''Teleoceras'' went extinct in North America alongside '' Aphelops'' at the end of the
Hemphillian
The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered t ...
, most likely due to rapid climate cooling, increased seasonality and expansion of C4 grasses, as isotopic evidence suggests that the uptake of C4 plants was far less than that in contemporary horses. The Gray Fossil Site in northeast
Tennessee
Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...
, dated to 4.5-5 million years ago, hosts one of the latest-known populations of ''Teleoceras,'' ''Teleoceras aepysoma.''
Description
''Teleoceras'' had much shorter legs than modern rhinos, and a barrel chest, making its build more like that of a
hippopotamus
The hippopotamus (''Hippopotamus amphibius;'' ; : hippopotamuses), often shortened to hippo (: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Sahar ...
than a modern rhino. Based on this description, Henry Fairfield Osborn suggested in 1898 that it was semi-aquatic and hippo-like in habits. This idea persisted for about a century, but has recently been discounted by isotopic evidence.
Some species of ''Teleoceras'' have a small nasal horn, but this appears to be absent in other species such as ''T. aepysoma''. ''Teleoceras'' has high crowned ( hypsodont) molar teeth, which has historically led to suggestions that the species were grazers. Dental microwear and mesowear analysis alternatively suggest a
browsing
Browsing is a kind of orienting strategy. It is supposed to identify something of relevance for the browsing organism. In context of humans, it is a metaphor taken from the animal kingdom. It is used, for example, about people browsing open sh ...
or mixed feeding (both browsing and grazing) diet. Carbon and oxygen isotope analysis of tooth enamel suggests hippo-like grazing habits, but not aquatic. However, δ18O measurements from Ashfall suggest that the species ''T. major'' was semi-aquatic.
Sexual dimorphism
''Teleoceras'' was sexually dimorphic. Males were larger, with larger tusks (lower incisors), a more massive head and neck, and significantly larger forelimbs. As a result of bimaturism, females matured and stopped growing before males, which is often seen in extant polygynous mammals. Males may have fought for mating rights; healed wounds on skulls have been observed, and healed broken ribs are not uncommon (although not all have their sexes determined). This is further supported by the breeding age female-to-male ratio in the Ashfall Fossil Beds being 4.25:1. There is also a rarity of young adult males preserved at Ashfall, which may be accounted for if they formed bachelor herds away from females and dominant bulls.
Discovery
Ashfall Fossil Beds
''Teleoceras major'' is the most common fossil in the Ashfall Fossil Beds of
Nebraska
Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...
. Over 100 intact ''T. major'' skeletons are preserved in ash from the Bruneau-Jarbidgesupervolcanic eruption. Of the 20+ taxa present, ''T. major'' was buried above the rest, being the last of the animals to succumb (small animals died faster), several weeks or months after the pyroclastic airfall event. Their skeletons show evidence of bone disease, ie hypertrophic pulmonary osteodystrophy (HPOD), as a result of lung failure from the fine volcanic ash.
Most of the skeletons are adult females and young, the breeding age female-to-male ratio being 4.25:1. There is also a rarity of young adult males. If the rhinos at Ashfall represent a herd, this may be accounted for if young adult males formed bachelor herds away from females and dominant bulls. The age demographic is very similar to that of modern
hippo
The hippopotamus (''Hippopotamus amphibius;'' ; : hippopotamuses), often shortened to hippo (: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic Mammal, mammal native to su ...
herds, as amongst the skeletons, 54% are immature, 30% are young adults, and 16% are older adults.
The greatest concentration of Ashfall fossils is housed in a building called the "Rhino Barn", due to the prevalence of ''T. major'' skeletons at the site, of which most were preserved in a nearly complete state. One extraordinary specimen includes the remains of a ''Teleoceras'' calf trying to suckle from its mother.
References
Bibliography
* McKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York, 631 pp.
* Prothero, Donald R. 2005. ''The Evolution of North American Rhinoceroses.'' Cambridge University Press, Cambridge, 218 pp.