Biology:Megacerops

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Megacerops ("large-horned face", from méga- "large" + kéras "horn" + ōps "face") is an extinct genus of odd-toed ungulate (hoofed mammal) belonging to the family Brontotheriidae, an extinct group of rhinoceros-like browsers related to horses. It was endemic to North America during the Late Eocene epoch (38–33.9 mya), existing for approximately 4.1 million years.[1]

Taxonomy

Megacerops was named by Leidy (1870). Its type species is Megacerops coloradensis. It was synonymized subjectively with Menodus by Clark and Beerbower (1967). It was assigned to Brontotheriidae by Leidy (1870), Carroll (1988), Mader (1989), and Mader (1998).[2][3]

According to Mihlbachler and others,[4][5] Megacerops includes the species of the genera Menodus, Brontotherium, Brontops, Menops, Ateleodon, and Oreinotherium.

Description

Restoration of M. coloradensis
Megacerops head reconstruction at the American Museum of Natural History

All of the species had a pair of blunt horns on their snout (the size varying between species), with the horns of males being much longer than those of the females. This could indicate that they were social animals which butted heads for breeding privileges.

Despite resembling the rhinoceros, it was larger than any living rhinoceros: the living animal easily approached the size of the African forest elephant, the third-largest land animal today. It stood about 2.5 m (8 ft 2 in) tall at the shoulders with an overall length (including tail) of 4.63 m (15.2 ft).[6]: 666  Its skull reached 89.5 cm (35.2 in) in greatest length, with some specimens possessing substantial canines, up to 70 mm long.[6]: 494, 523  Megacerops resembled a large rhinoceros, possessing blunt Y-shaped horn-like protrusions on its nose up to 43 cm in length.[6]: 553  Its mass is estimated to be in the range of 3.3–3.8 t (3.6–4.2 short tons) [7][8]

The dorsal vertebrae above the shoulders had extra long spines to support the huge neck muscles needed to carry the heavy skull. The shape of its teeth suggests that it preferred food such as soft stems and leaves, rather than tough vegetation. It may have had fleshy lips and a long tongue for carefully selecting food.

Paleobiology

AMNH 518, from South Dakota. This M. coloradensis specimen has a healed broken rib, not pictured here.

The skeleton of an adult male was found with partially healed rib fractures, which supports the theory that males used their 'horns' to fight each other. No creature living in Megacerops' time and area except another Megacerops could have inflicted such an injury.[9] The breathing movements prevented the fractures from completely healing. The adults may have also used their horns to defend themselves and their calves from predators, such as hyaenodonts, entelodonts, Bathornis or nimravids.

Oxygen isotope analysis of Megacerops tooth enamel from the White River assemblage has found them to have low δ18O values, which likely reflects the preference of the genus for moist environments.[10]

Distribution

Fossils were uncovered in the northern plains states. Life-sized models of Megacerops families (a male, female, and juvenile) are displayed at the James E. Martin Paleontological Research Laboratory, South Dakota School of Mines & Technology, and a different set at the Canadian Museum of Nature.

Many remains have been found in South Dakota and Nebraska. In the past, specimens exposed by severe rainstorms were found by Native Americans of the Sioux tribes. The Sioux called them "thunder beasts", a name preserved in the ancient Greek translation (bronto-, thunder; therion, beast).[11] Many of the skeletons found by the Sioux belonged to herds which were killed by volcanic eruptions of the Rocky Mountains, which were volcanically active at the time.

See also

References

  1. ↑ "PBDB Taxon". https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=43043. 
  2. ↑ J. Clark and J. R. Beerbower. 1967. Geology, paleoecology, and paleoclimatology of the Chadron Formation. Fieldiana
  3. ↑ Carroll, Robert L. (1988). Vertebrate Paleontology and Evolution. Freeman. ISBN 978-0-7167-1822-2. 
  4. ↑ Mihlbachler, M.C., Lucas, S.G., and Emry, R.J. (2004). "The holotype specimen of Menodus giganteus, and the "insoluble" problem of Chadronian brontothere taxonomy". New Mexico Museum of Natural History and Science Bulletin 26: 129–136. https://books.google.com/books?id=fJivCQAAQBAJ&pg=PA129. 
  5. ↑ Mihlbachler, Matthew Christian (2005). Phylogenetic systematics of the Brontotheriidae (Mammalia, Perissodactyla) (Thesis). OCLC 79487069. ProQuest 305015315.
  6. ↑ 6.0 6.1 6.2 Osborn, Henry F. (1929). The titanotheres of ancient Wyoming, Dakota, and Nebraska. Dept. of the Interior, U.S. Geological Survey. https://archive.org/details/titanotheresofan01osbo/. 
  7. ↑ Gregory S., Paul. "Mass estimate table". http://www.gspauldino.com/data.html. 
  8. ↑ Bales, Gerald S. (1996). "Heterochrony in Brontothere Horn Evolution: Allometric Interpretations and the Effect of Life History Scaling". Paleobiology 22 (4): 481–495. doi:10.1017/S009483730001647X. Bibcode: 1996Pbio...22..481B. https://www.cambridge.org/core/journals/paleobiology/article/abs/heterochrony-in-brontothere-horn-evolution-allometric-interpretations-and-the-effect-of-life-history-scaling/3E46D81D1562F29022571A657955382A. Retrieved September 26, 2022. 
  9. ↑ Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 258–259. ISBN 978-1-84028-152-1. 
  10. ↑ Zanazzi, Alessandro; Kohn, Matthew J. (7 January 2008). "Ecology and physiology of White River mammals based on stable isotope ratios of teeth" (in en). Palaeogeography, Palaeoclimatology, Palaeoecology 257 (1-2): 22–37. doi:10.1016/j.palaeo.2007.08.007. https://www.sciencedirect.com/science/article/abs/pii/S003101820700449X. Retrieved 27 September 2025. 
  11. ↑ Mayor, Adrienne. "Placenames Describing Fossils in Oral Traditions". https://web.stanford.edu/dept/HPS/MayorPlacenames.pdf. 

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