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18.12.2015 16:55 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.16 Notoungulates,Chalicotheriidae,or what happens when nature play
Автор: valentint Категория: Забавление   
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Notoungulates (Notoungulata)
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Notoungulates –  literally “southern ungulates.” – may be the most emblematic of all extinct South American mammals. Notoungulates were the most abundant of the native South American ungulates, and probably more species of notoungulates have been named than all other groups of endemic ungulates combined. The group includes more than 150 extinct genera in around a dozen families. Notoungulates lived throughout most of South America for nearly the entire Cenozoic, but only the toxodontid Mixotoxodon ever expanded its range into another continent; in the Pleistocene, this animal lived in Central America and the extreme southern United States. Unlike litopterns, notoungulates have not yet been found in Eocene deposits of Antarctica. This is surprising considering the abundance of notoungulates at many South American fossil sites of this age.
Notoungulates are united by characters of their ear region and their teeth, including the presence of a loph on their upper molars known as the “crochet”. A group of Paleogene mammals from the Northern Hemisphere known as arctostylopids were once thought to be closely related to notoungulates, but it now appears that dental similarities evolved independently in the two groups. Thus, with the exception of Mixotoxodon, the notoungulate radiation was exclusively a South American phenomenon.
Cifelli’s (1993) analysis of notoungulate relationships suggested that notoungulates can be divided into two main groups (suborders), Toxodontia and Typotheria, plus two early-diverging notoungulate families. By and large this arrangement  has been supported by more recent studies of notoungulate evolutionary relationships such as that of Billet (2011). However, this and other studies have highlighted the fact that several traditionally-recognized families probably are not natural (monophyletic) groups. In other words, some of their species appear to be more closely related to those in other families than other species in their own family. These families of more questionable status include Henricosborniidae, Isotemnidae, Notohippidae, Oldfieldthomasiidae, and Archaeohyracidae. With the exception of Notohippidae, remains of these families are only found at sites older than Miocene in age (23 million years old).
The suborder Toxodontia mostly includes large (sheep-sized) to very large (hippopotamus-sized) species. It is named for the family Toxodontidae, which itself is named for Toxodon, a genus of mammals that  survived until the Pleistocene megafaunal extinction some 12,000 years ago. This genus, family, and suborder were all named by the great English anatomist Richard Owen based on fossils collected by none other than Charles Darwin. Three toxodont families survived well into the Miocene: Homalodotheriidae, Leontiniidae, and Toxodontidae. Among these, only the toxodontids were widespread, abundant, and diverse during this interval. They were also the only toxodonts still living in South America during the Great American Biotic Interchange.
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The suborder Typotheria mainly includes small (rabbit-sized) to medium (dog-sized) species, many of which have rodent or rabbit-like cranial and/or skeletal features. This group was also named for one of its most recent and largest members, Typotherium, which is now known as Mesotherium. Ancestrally, typotheres are characterized by a  “face” pattern of enamel-lined fossettes in their upper teeth (see below). As is true of toxodonts, three typothere families persisted well into the Miocene: Interatheriidae, Mesotheriidae, and Hegetotheriidae. However, all three of these were rather widespread and abundant during this interval, and the latter two survived into the Pleistocene.
The four major families of Miocene notoungulates (Toxodontidae, Interatheriidae, Mesotheriidae, and Hegetotheriidae) all independently evolved simplified, ever-growing (hypselodont) cheek teeth. They are the only ungulates other than certain giant rhinoceroses (Elasmotherium spp.) to do so. Early members of these groups, as well as other hypsodont  notoungulates, can often be distinguished by the pattern of enamel-lined structures on their molars. When a mammal tooth erupts, it has a continuous covering of enamel. However, in many herbivores that eat abrasive foods, the enamel covering on the surface wears away, exposing the dentine underneath. (Humans and other mammals that eat relatively soft foods generally maintain the enamel covering throughout their lifetime.) If the enamel on the surface of a tooth extends downward into the tooth crown during development to form a pit, the pits are left behind as enamel “islands” once the remaining enamel on the surface of the tooth wears away. These islands of enamel that are surrounded by dentine are known as fossae (singular: fossa) or fossettes in upper teeth and fossettids in lower teeth. Ancestrally, a slightly worn typothere tooth has a characteristic pattern of fossettes that resembles a face; the large, central fossa is the “mouth,” and the two labial or buccal fossettes are the “eyes.” This pattern is not usually visible in unworn teeth, nor can it be seen in heavily worn teeth. In later-diverging typotheres, this ancestral condition has been modified to such a degree that it is no longer recognizable at all. Very hypsodont (or hypselodont) species have lost all enamel islands due to developmental constraints; the only similar structures are folds of enamel that extend inward from the lingual and/or buccal surface of their tooth.



Although is not complete, the preserved fossils suggests that Mixotoxodon were the most massive member of the group, with a weight about 3.8 tonnes
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Mixotoxodon is known by fragmentary remains, usually mandible fragments and teeth. Although the general appearance probably was very similar to the another toxodontid from the Pleistocene, the better known Toxodon, their fossils shown that the outer borders of the symphysis in the lower jaw don"t diverge anteriorly, and the incisors form a semicircular structure that protrude less than the incisives of Toxodon; the snout was cylindrical, instead of the broad hippo-like muzzle of Toxodon. The straight snout and the narrow lower incisors closely packed, suggest that this animal had a different feeding strategy compared to their southern relative, although the teeth of both genera was adapted to deal with abrasive food.It was a rhino-sized animal, with a weight of up to 3.8 tonnes, which make it the largest member of Notoungulata.
Mixotoxodon is known from a single species M. larensis. Mixotoxodon is the only notoungulate known to have migrated out of South America during the Great American Interchange. Its fossils have been found in northern South America, in Central America, in Veracruz and Michoacбn, Mexico (with a possible find in Tamaulipas), and eastern Texas, USA.
The genus was also one of the last surviving notoungulates, along with related genera such as the better-known Toxodon. The name refers to the fact that Mixotoxodon combines characteristics typical of different toxodontid subfamilies.


The largest notoungulate known of complete remains is Toxodon.
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1. Homalodotherium cunninghanni 2. Rhynchippus equinus 3. Toxodon platensis
It was about 2.7 metres (8.9 feet) in body length, and about 1.5 metres (4.9 feet) high at the shoulder and resembled a heavy rhinoceros. Toxodon (meaning "bow tooth") is an extinct mammal of the late Pliocene and Pleistocene epochs from about 2.6 million to 16,500 years ago.It is a member of Notoungulata, one of several now extinct orders of hoofed mammals indigenous to South America. It was among the largest and last members of its order, and was probably the most common large-hoofed South American mammal of its time.

Charles Darwin
was one of the first to collect Toxodon fossils, after paying 18 pence for a T. platensis skull from a farmer in Uruguay. In The Voyage of the Beagle Darwin wrote "November 26th - I set out on my return in a direct line for Monte Video. Having heard of some giant"s bones at a neighbouring farm-house on the Sarandis, a small stream entering the Rio Negro, I rode there accompanied by my host, and purchased for the value of eighteen pence the head of the Toxodon." Since Darwin discovered that the fossils of similar mammals of South America were different from those in Europe, he invoked many debates about the evolution and natural selection of animals.

Analysis of collagen sequences obtained from Toxodon as well as from Macrauchenia found that South America"s native notoungulates and litopterns form a sister group to perissodactyls, making them true ungulates.
Toxodon was about 2.7 m (8 ft 10 in) in body length, with an estimated weight up to 1,500 kg (3,300 lb) and about 1.5 m (4 ft 11 in) high at the shoulder and resembled a heavy rhinoceros, with a short and vaguely hippopotamus-like head. Because of the position of its nasal openings, it is believed that Toxodon had a well-developed snout. It had a massive skeleton, which suggests that it supported a large muscular body. It had short stout legs with three functional toes, with most of the body weight being borne by the central toe.
The vertebrae were equipped with high apophyses, which most likely supported the massive weight and muscles as well as its powerful head. Toxodon had broad jaws which were filled with bow shaped teeth and incisors. These teeth would have allowed the animal to tear through and bite off the plants and leaves.
It was initially believed to have been amphibious, but after examining the proportions of the femur and tibia, as well as the position of its head, below the top of the spinal column, palaeontologists realized that it had features similar to terrestrial animals such as elephants or rhinoceroses. The fossils are also usually found in arid and semi-arid areas, typically an indication of a primarily terrestrial life.
Toxodon would have had a very unusual gait, due to its peculiar proportions. It may have galloped to escape predators, but like a rhino, it probably relied more on its size as protection against predators.


Chalicotheriidae
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Chalicotheres are an unusual group of extinct fossil perissodactyls that, despite a dentition suited for a herbivorous diet, had claws on their digits instead of hooves. The group first appeared in the Eocene, reached its highest diversity in the Miocene, and went extinct in the Pleistocene. Chalicotheres seem to have undergone much of their diversification in Asia but are also found in Europe, Africa, and North America. Oligocene and later chalicotheres belong to the family, which includes two subfamilies, the Chalicotheriinae and Schizotheriinae.
Unlike modern perissodactyls, chalicotheres had long forelimbs and short hind limbs. Consequently, chalicotheres probably moved with most of their weight on their short, strong hind legs. Their front legs had long, curved claws indicating they knuckle-walked like giant anteaters today. Fossil remains have shown thick, developed front knuckles. It was once thought that the claws were used to dig up roots and tubers, but the wear on the claws and teeth do not suggest that they dug or ate dirt-rich foods such as tubers. The chalicotheres probably used their claws to strip vegetation from trees and to forage for food. Chalicotheres did not have front teeth in their upper jaw, and their back teeth show little wear, suggesting that they probably were selective browsers. It used its long forearms and curved claws to hook down leafy branches in the wooded savannahs in which it lived.
The chalicotheres" lifestyle, anatomical design, posture, and locomotion are very different from those of virtually all quadrupedal ungulates, indicating convergence with other large, partially bipedal mammals such as ground sloths, great apes, and bears (especially giant pandas).
They evolved around 46 million years ago from small forest animals similar to the early horses. Many chalicotheres, including such animals as Moropus and Chalicotherium, reached the size of a horse. By the late Oligocene, they had divided into two groups: one that grazed in open areas and another that was more adapted to woodlands. They died out around 781,000 years ago, with Nestoritherium being the most recently dated chalicothere.Chalicotheres are related to the extinct brontotheres, as well as to modern day horses, rhinoceroses, and tapirs.


Borissiakia
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Borissiakia is an extinct genus of chalicothere, a group of herbivorous, odd-toed ungulate (perissodactyl) mammals.That lived during the late Oligocene and have a very large size - their body length reaches about 4 m, but when they went on the hind legs, then "grows" up to 5 m He is a typical representative of a peculiar superfamily halikoterioidey (Chalicotherioidea) imparidigitate unit , for the representatives of which is characterized by the formation of large claws , especially on the front legs instead of hooves . In addition , the hind legs of these massive mammals were shorter than the front . Borissyakiya as other halikoteriya , it feeds on the leaves and young shoots of trees , standing on hind legs and leaning on tree trunks forelegs. The general structure of the skull close borissyakiya largest horses in the structure of the teeth - brontoteriidam . The representatives of the superfamily have been widely distributed throughout the Oligocene and Miocene in Mongolia , Kazakhstan, Europe, North Africa and North America . Borissiakia betpakdalensis lived in the Late Oligocene in the territory of Central Kazakhstan.


Moropus

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1. Chalicotherium goldfussi 2. Moropus distans 3. Ancylotherium hennigi
Moropus  is an extinct genus of mammal, belonging to a group called chalicotheres, which were perissodactyl ("odd-toed") mammals, endemic to North America during the Miocene, existing for approximately 9.4 million years.
Size: 3,3 m in length, 240 cm in height, 1000kg of weight.
Moropus is related to the modern horse, rhino, and tapir. Like other chalicotheres, they differed from their modern relatives in having large claws, rather than hooves, on the front feet; these claws may have been used for defense or digging for food. Moropus stood about (2.4 m tall at the shoulder. The three highly compressed claw-like hooves on each foot were split down the middle. These claws actually gave Moropus its name: " slow "or "sloth foot". This name implies that because of the claws, Moropus was a clumsy mover. But the articulation of the phalangeal (finger) bones, in addition to probable large foot and toe pads, shows that Moropus probably could raise the claws slightly to enable it to move about quite smoothly. Because the hooves curve inward, it probably had a pigeon-toed gait.

 

Anisodon grande (Chalicotherium grande )
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Anisodon, formerly known as Chalicotherium grande, lived in Europe during the Miocene. It was a king-size animal: the growth in the shoulders - 180 cm, weight is about 600 kg. Relatively short hind legs with hooves and long front legs with huge claws makes him not very harmonious outwardly, but quite adapted to life at that time. His clawed forepaws allowed to reach high branches, and claws can dig up the roots and tubers of plants. These legs also allows very effectively defend themselves from predators. Anatomically Chalicotheriidae closest to rhinos and horses, and the combination of more elongated forelimbs, compared with the hind legs, and the presence of claws presuppose that these animals were not fast runners. Some scientists consider the possibility of Chalicotheriidae even sitting position at rest. Chalicotheriidae occupying a unique ecological niches, morphologically divided into two types.The first type - Schizotheriinae with more high-coronal teeth and looks similar to horses (Moropus  and Tylocephalonyx, who had a strange dome-shaped thickening of the skull). By the beginning of the Pliocene they became extinct except surviving in Africa Ancylotherium.
The second group - the Chalicotheriinae to which belonged Anisodon. Their body proportions were like a gorilla or giant ground sloth. Their greatest diversity is observed in the late Miocene.

 














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