Aphelops | |
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Skeleton in Nebraska State Museum of Natural History | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Perissodactyla |
Family: | Rhinocerotidae |
Subfamily: | † Aceratheriinae |
Genus: | † Aphelops Owen, 1845 |
Type species | |
†Aphelops megalodus Cope, 1873 (as Aceratherium megalodum ) | |
Species | |
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Aphelops (Greek: "smooth" (apheles), "face" (ops), in a reference of lacking a horn [1] ) is an extinct genus of hornless rhinocerotids endemic to North America. It lived from the Middle Miocene to the early Pliocene, during which it was a common component of North American mammalian faunas along with Teleoceras . [2]
On the basis of skull size, the largest species of Aphelops is A. mutilus (which is the largest North American rhinoceros) [3] and the smallest is the type species A. megalodus. [4] A. mutilus has been estimated to have weighed 764–1,762 kilograms (1,684–3,885 lb), [5] and A. malacorhinus has been estimated at 889 kilograms (1,960 lb). [6]
Aphelops can be distinguished by other members of the Aceratheriinae by two traits: the arched top of the skull, and the long diastema (gap) between the second incisor (lower tusk) and first premolar. Many other aspects of its anatomy are typical of aceratheriines, including: the absence of a horn on the broad, unfused nasal bones; the reduced premaxilla and lost first incisor; a nasal incision (or notch below the nasal bones) reaching at least the level of the fourth premolar; a triangular-shaped skull when viewed from the rear; narrow zygomatic arches; brachydont or low-crowned teeth without cement; upper molars bearing a fold of enamel known as an anterocrochet; and lower tusks that are subcircular in cross-section. [4]
More derived (specialized) species have larger teeth and longer, more slender nasal bones (also producing a larger incision). The various species also differ in the depth of the nasal incision: in A. megalodus, it reaches the front of the fourth premolar; in A. malacorhinus, it reaches the rear of that tooth; and in A. mutilus, it reaches the first molar. [4] [3]
The lower tusks of Aphelops are informative about the sex and age of individuals, as in Teleoceras: males have much thicker tusks, [7] [8] while older individuals have more strongly erupted tusks showing more extensive wear patterns. The stages in the eruption of the molar-like cheek teeth were identical to living rhinos. These factors were used by Matthew Mihlbacher in 2003 to analyze a bone bed of Aphelops known as the Love Island bonebed; adults (between 35% and 68% of maximum lifespan) are most common, there appears to be no male bias, and young males are rare. This is unlike Teleoceras, where young males are disproportionately preserved in bone beds. Such a difference may imply different social behaviour: young male Aphelops perhaps died less frequently from fighting, and used different kinds of ritualistic displays. Aphelops were probably not completely monogamous, with the degree of sexual dimorphism being suggestive of polygyny. [7]
Aphelops is thought to have been a browser on C3 plants, like the modern black rhinoceros, with its longer limbs adapted to traversing open, brushy country. Isotopic evidence suggests that, in the late Miocene, Teleoceras had limited intake on newly-emergent C4 grasses, but Aphelops continued to browse. [6] [2] This difference in feeding ecologies explains how they could coexist sympatrically across many environments for 13 million years. Both went extinct at the end of the Hemphillian North American land mammal age, most likely due to rapid climate cooling, increased seasonality and expansion of C4 grasses. [2]
The Desmostylia are an extinct order of aquatic mammals native to the North Pacific from the early Oligocene (Rupelian) to the late Miocene (Tortonian). Desmostylians are the only known extinct order of marine mammals.
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Teleoceras is an extinct genus of rhinocerotid. It lived in North America during the Miocene and Pliocene epochs during the Hemingfordian to the end of Hemphillian from around 17.5 to 4.9 million years ago. It grew up to lengths of 13 feet long).
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Epicyon is a large, extinct, canid genus of the subfamily Borophaginae, native to North America. Epicyon existed for about 15 million years from the Hemingfordian age of the Early Miocene, to the Hemphillian of the Late Miocene. Epicyon is the largest known canid of all time, with the type species reaching 2.4 m (7.9 ft) in length, 90 cm (35 in) in shoulder height and approximately 100–125 kg (220–276 lb) in body mass. The largest known humerus specimen belonged to an individual weighing up to 170 kg (370 lb).
Desmostylus is an extinct genus of herbivorous mammal of the family Desmostylidae living from the Chattian stage of the Late Oligocene subepoch through the Late Miocene subepoch and in existence for approximately 21.2 million years.
Anancus is an extinct genus of "tetralophodont gomphothere" native to Afro-Eurasia, that lived from the Tortonian stage of the late Miocene until its extinction during the Early Pleistocene, roughly from 8.5–2 million years ago.
Cuvieronius is an extinct New World genus of gomphothere which ranged from southern North America to western South America during the Pleistocene epoch. Among the last gomphotheres, it became extinct at the end of the Pleistocene, approximately 12,000 years ago, following the arrival of humans to the Americas.
Protypotherium is an extinct genus of notoungulate mammals native to South America during the Oligocene and Miocene epochs. A number of closely related animals date back further, to the Eocene. Fossils of Protypotherium have been found in the Deseadan Fray Bentos Formation of Uruguay, Muyu Huasi and Nazareno Formations of Bolivia, Cura-Mallín and Río Frías Formations of Chile, and Santa Cruz, Salicas, Ituzaingó, Aisol, Cerro Azul, Cerro Bandera, Cerro Boleadoras, Chichinales, Sarmiento and Collón Curá Formations of Argentina.
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Iranotherium is an extinct genus of large elasmotheriine rhinocerotids, comparable in size to a modern white rhino. It is known from the Late Miocene (Tortonian) of Maragha, Iran and the middle part of the Liushu formation of northwestern China. It was a precursor to the related Sinotherium and may have been ultimately outcompeted by its descendant. This species is most well known for showing unique sexual dimorphism among rhinos.
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Hilarcotherium is an extinct genus of astrapotheriid mammals that lived in South America during the Middle Miocene (Laventan). The type species is H. castanedaii, found in sediments of the La Victoria Formation, part of the Honda Group in the department of Tolima in Colombia. In 2018, Carrillo et al. described a partial skull and mandible of a second species H. miyou from the Castilletes Formation in the Cocinetas Basin of northern Colombia, and estimated the body weight of the animal at 6,465 kilograms (14,253 lb).
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