Teleoceras

Teleoceras is an extinct genus of rhinocerotid endemic to North America during the Neogene (Miocene and Pliocene).

Taxonomy

Teleoceras is derived from Greek: "perfect" (teleos) & "horn" (keratos).<ref>Template:Cite web</ref>

Description

Template:Multiple image Teleoceras had much shorter legs than modern rhinos, and a barrel chest, making its build more like that of a hippopotamus than a modern rhino. It grew up to lengths of Template:Convert long.<ref>Template:Cite web</ref> T. major was found to have been sexually dimorphic, with males being larger than females. Based on the most reliable method, non-length longbones, males could’ve weighed Template:Convert, while females were estimated to have weighed Template:Convert.<ref name=":0">Template:Cite journal</ref>

Some species of Teleoceras have a small nasal horn, but this appears to be absent in other species such as T. aepysoma.<ref>Template:Cite journal</ref> Template:Multiple image

Behavior and Paleoecology

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 or mixed feeding (both browsing and grazing) diet.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Whether or not Teleoceras was semi-aquatic had been debated by experts. Based on this description, Henry Fairfield Osborn suggested in 1898 that it was semi-aquatic and hippo-like in habits, however and oxygen isotope analysis of tooth enamel suggests hippo-like grazing habits, but not aquatic.<ref name=":0" /><ref>Template:Cite journal</ref> However, δ¹⁸O measurements from Ashfall suggest that the species T. major was semi-aquatic.<ref>Template:Cite journal</ref><ref>Template:Cite web</ref><ref>Template:Cite journal</ref> Further evidence of the dependence on water of T. major comes from combined studies of its enamel ⁸⁷Sr/⁸⁶Sr, δ¹³C, and δ¹⁸O, which show its lifetime movement patterns were mostly restricted to areas with high water availability.<ref>Template:Cite journal</ref>

Social behavior

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.<ref name=":0" />

Paleoenvironment

Teleoceras was endemic to North America during the Miocene during the Hemingfordian faunal stage to the end of Hemphillian faunal stage from around 17.5 to 4.9 million years ago,<ref name="wang2020">Template:Cite journal</ref><ref>Template:Cite web</ref> and is considered an index fauna of the Hemphillian.<ref name=":2" /> However, several boundary / Blancan faunal stage specimens have been recovered from Pliocene era North America, including the Ringold Formation of Washington, the Beck Ranch fauna of Texas, the Pipe Creek sinkhole fauna of Indiana and the Saw Rock Canyon fauna of Kansas.<ref name=":2">Template:Cite journal</ref><ref name=":1">Template:Cite journal</ref>

The presence of Plionarctos and Teleoceras have been used to constrain the temporal ages of the Gray Fossil Site, Palmetto fauna and Pipe Creek Sinkhole to the Hemphillian (between 7Mya and 4.5Mya, late Miocene to early Pliocene),<ref name=":22">Template:Cite journal</ref><ref>Template:Cite journal</ref> however specimens of these index fossils younger than 4.5Mya put this temporal bracketing in doubt.<ref>Template:Cite journal</ref>

Important sites

Ashfall Fossil Beds

Teleoceras major is the most common fossil in the Ashfall Fossil Beds of Nebraska. Over 100 intact T. major skeletons are preserved in ash from the Bruneau-Jarbidge supervolcanic 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, i.e. hypertrophic pulmonary osteodystrophy (HPOD), as a result of lung failure from the fine volcanic ash.<ref>Template:Citation</ref>

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 herds, as amongst the skeletons, 54% are immature, 30% are young adults, and 16% are older adults.<ref name=":0" />

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.<ref>Template:Cite web</ref>

Gray Fossil Site

The Gray Fossil Site in northeast Tennessee, dated to 4.5-5 million years ago, hosts one of the latest-known populations of Teleoceras, Teleoceras aepysoma.<ref>Template:Cite journal</ref>

Extinction

Teleoceras is typically though to have gone extinct in North America (alongside Aphelops) at the end of the Hemphillian, 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.<ref name="wang2020" /> However, Blancan age specimens may be younger than 4.5 million years old, and may be as young as 3.5 million years old (although some sites are disputed).<ref name=":2" /><ref name=":1" />

References

Bibliography

• McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. Template:ISBN
• Prothero, Donald R. 2005. The Evolution of North American Rhinoceroses. Cambridge University Press, Cambridge, 218 pp. Template:ISBN