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]
Proboscidea is a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. Three species of elephant are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant.
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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Platybelodon is an extinct genus of large herbivorous proboscidean mammals related to modern-day elephants, placed in the "shovel tusker" family Amebelodontidae. Species lived during the middle Miocene Epoch in Africa, Asia and the Caucasus.
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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.
Gomphotheres are an extinct group of proboscideans related to modern elephants. First appearing in Africa during the Oligocene, they dispersed into Eurasia and North America during the Miocene and arrived in South America during the Pleistocene as part of the Great American Interchange. Gomphotheres are a paraphyletic group ancestral to Elephantidae, which contains modern elephants, as well as Stegodontidae.
Marginocephalia is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. There are two clades included in Marginocephalia: the thick-skulled Pachycephalosauria and the horned Ceratopsia. All members of Marginocephalia were primarily herbivores. They basally used gastroliths to aid in digestion of tough plant matter until they convergently evolved tooth batteries in Neoceratopsia and Pachycephalosauria. Marginocephalia first evolved in the Jurassic Period and became more common in the Cretaceous. They are basally small facultative quadrupeds while derived members of the group are large obligate quadrupeds. Primitive marginocephalians are found in Asia, but the group migrated upwards into North America.
Paraceratherium is an extinct genus of hornless rhinocerotoids belonging to the family Paraceratheriidae. It is one of the largest terrestrial mammals that has ever existed and lived from the early to late Oligocene epoch. The first fossils were discovered in what is now Pakistan, and remains have been found across Eurasia between China and the Balkans. Paraceratherium means "near the hornless beast", in reference to Aceratherium, the genus in which the type species P. bugtiense was originally placed.
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 haydeni 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.
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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Aceratherium is an extinct genus of rhinocerotid of the subfamily Aceratheriinae that lived in Eurasia during the Miocene.
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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