''Megacerops'' ("large-horned face", from '' méga-'' "large" + '' kéras'' "horn" + '' ōps'' "face") 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 the prehistoric

odd-toed ungulate Perissodactyla (, ), or odd-toed ungulates, is an order of ungulates. The order includes about 17 living species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They t ...

(hoofed mammal)

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Brontotheriidae Brontotheriidae is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially, they looked rather like rhinos with some developing bony nose horns, and were some of ...

, an extinct group of

rhinoceros 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 ...

-like browsers related to

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...

s. It was endemic to

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

Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...

epoch (38–33.9 mya), existing for approximately .

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). According to Mihlbachler and others, ''Megacerops'' includes the species of the genera ''Menodus'', ''Brontotherium'', ''Brontops'', ''Menops'', ''Ateleodon'', and ''Oreinotherium''.

Description

All of the species had a pair of blunt

horn Horn may refer to: Common uses * Horn (acoustic), a tapered sound guide ** Horn antenna ** Horn loudspeaker ** Vehicle horn ** Train horn *Horn (anatomy), a pointed, bony projection on the head of various animals * Horn (instrument), a family ...

s 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 African forest elephant (''Loxodonta cyclotis'') is one of the two living species of African elephant, along with the African bush elephant. It is native to humid tropical forests in West Africa and the Congo Basin. It is the smallest of the ...

, the third-largest land animal today. It stood about tall at the shoulders with an overall length (including tail) of . Its skull reached in greatest length, with some specimens possessing substantial canines, up to 70 mm long. ''Megacerops'' resembled a large rhinoceros, possessing blunt Y-shaped horn-like protrusions on its nose up to 43 cm in length. Its mass is estimated to be in the range of The dorsal

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e above the shoulders had extra long spines to support the huge neck muscles needed to carry the heavy

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

. 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

The skeleton of an adult male was found with partially healed

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

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. 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 Hyaenodontidae ("hyena teeth") is a family of placental mammals in the extinct superfamily Hyaenodontoidea. Hyaenodontids arose during the early Eocene and persisted well into the early Miocene. Fossils of this group have been found in Asia, Nor ...

entelodonts Entelodontidae is an extinct family of pig-like artiodactyls (even-toed ungulates) which inhabited the Northern Hemisphere (Asia, Europe, and North America) from the late Eocene to the early Miocene epochs, about 38-19 million years ago. Their la ...

, ''

Bathornis ''Bathornis'' ("tall bird") is an extinct genus of birds related to modern day seriemas, that lived in North America about 37–20 million years ago. Like the closely related and also extinct phorusrhacids, it was a flightless predator, occupying ...

'' or nimravids.

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 The Canadian Museum of Nature (; CMN) is a national museums of Canada, national natural history museum based in Canada's National Capital Region (Canada), National Capital Region. The museum's exhibitions and public programs are housed in the Vi ...

. Many remains have been found in

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state, state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota people, Dakota Sioux ...

and

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 ...

. In the past, specimens exposed by severe

rain Rain is a form of precipitation where water drop (liquid), droplets that have condensation, condensed from Water vapor#In Earth's atmosphere, atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is res ...

storms were found by Native Americans of the

Sioux The Sioux or Oceti Sakowin ( ; Dakota/ Lakota: ) are groups of Native American tribes and First Nations people from the Great Plains of North America. The Sioux have two major linguistic divisions: the Dakota and Lakota peoples (translati ...

tribes. The Sioux called them "thunder beasts", a name preserved in the ancient Greek translation (bronto-, ''thunder;'' therion, ''beast''). Many of the

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

s found by the Sioux belonged to

herd A herd is a social group of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is called '' herding''. These animals are known as gregarious animals. The term ''herd'' ...

s which were killed by

volcanic eruptions A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...

of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

, which were volcanically active at the time.

References

External links

Fast evolution of Megacerops after the end-Cretaceous mass extinction
12 May 2023,

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