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18.12.2015 17:55 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch.17 Brontotheriidae and Dinoceratans
Автор: valentint Категория: Забавление   
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Brontotheriidae
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Brontotheriidae, also called Titanotheriidae, is a family of extinct mammals belonging to the order Perissodactyla,the order that includes horses, rhinoceroses, and tapirs.They lived around 56–34 million years ago, until the very close of the Eocene.
Brontotheres retain four toes on their front feet and three toes on their hind feet. Their teeth are adapted to shearing (cutting) relatively nonabrasive vegetation. Their molars have a characteristic W-shaped ectoloph (outer shearing blade).
The evolutionary history of this group is well known, due to an excellent fossil record in North America.The earliest brontotheres, such as Eotitanops, were rather small, no more than a meter in height, and were hornless.
Brontotheres, over time, evolved massive body sizes, although some small species, such as Nanotitanops, did persist through the Eocene. Some genera, such as Dolichorhinus, evolved highly elongated skulls. Later brontotheres were massive in size, up to 2.5 m (8.2 ft) in height with bizarre horn-like skull appendages. For instance the North American brontothere Megacerops evolved large sexually dimorphic paired horns above their noses. The sexually dimorphic horns suggest that brontotheres were highly gregarious (social) and males may have performed some sort of head-clashing behavior in competition for mates. However, unlike rhinos, the horns of brontotheres are composed of bone, the frontal bone and nasal bone, and were placed side-to-side rather than front-to-back.

Megacerops
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Megacerops is an extinct genus of the prehistoric odd-toed ungulate (hoofed mammal) 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.
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 larger than those of the females. This could indicate that they were social animals which butted heads for breeding privileges.
Despite resembling a 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 (8.2 ft)tall at the shoulders and the body, including the head, could measure 5 m (16 ft) in length.It resembled a large rhinoceros, possessing a Y-shaped horn-like protrusion on its nose, with blunt ends. One specimen is estimated to have weighed 3.3 t (3.6 short tons) by Gregory S. Paul
The dorsal vertebrae above the shoulders had extra long spines to support the huge neck muscles needed to carry the heavy skull. Possibly, it had fleshy lips and a long tongue, perfect for carefully selecting food. The shape of its teeth suggests that it preferred food such as soft stems and leaves, rather than tough vegetation.
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.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 creodonts or nimravids.


Embolotherium
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As an Asian brontothere, Embolotherium rivals large North American species like Megacerops in terms of size. However a full skeleton of Embolotherium remains unknown to science and this conclusion is based upon comparison of the known parts of Embolotherium with the more complete remains of other brontotheres.

Whereas many brontotheres have ornamentation on top of their heads, Embolotherium did not have individual horns but a single plate that rose up from the tip of the snout, the inspiration for the battering ram part of its name. Interestingly there does not seem to be any difference between males and females on the basis that all known skulls, even those of juveniles have this feature. This plate has a lightweight construction which pretty much rules out the possibility that it was a weapon used in dominance contests. More likely the plate was a display device that allowed Embolotherium individuals to signal to one another, as well as identify members of their own species from other similar species and animals. Another product of this nasal feature however is that the nasal cavity shows considerable enlargement which has led to the suggestion that Embolotherium may have had a resonating chamber for amplyfying the sound of its calls.

Embolotherium seems to have been better adapted to eating softer vegetation since overall the teeth are better adapted for sheering rather than grinding plants. The forward incisor teeth are not especially well developed which further suggests that Embolotherium fed upon plant parts that would not require a great deal of effort (and hence less strain on teeth) to pull free. Much of Asia during the early Eocene was at a lower elevation than it is today which resulted in more extensive areas of wetland. It is likely that Embolotherium roamed around these habitats browsing from the soft vegetation that would grow here.
By the end of the Eocene the climate of Asia was becoming drier, a process that was the result of the rising Himalaya Mountains elevating the land and draining the low lying areas. This saw an environmental shift towards a plains environment with different types of plants that Embolotherium was less suited to. On top of this new herbivores were adapting to take advantage of these new plants which resulted in additional competition which saw Embolotherium edged into extinction.


Aktautitan
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Dimensions: length – 4.5-5 m, height - 250 сm, weight - 4200 - 5000 kg

Aktautitan is an extinct animal from equines Brontotheriidae family, who lived in the middle Eocene. This animal got its generic name is in honor of Aktau mountains in Kazakhstan, where its fossils were found. They are found far to the west of the Gobi Desert, where most of the detected Asian brontotheres. There are three known Aktautitan"s skull with small fronto-nasal appendages and individual bones of the body. Probably it was one of the major representatives of Brontotheriidae: its height at the withers could reach 2.5 m. Were also found trace track of the large equines that could belong to this species. Judging by the structure of the teeth, Aktautitan fed soft vegetation - leaves and young shoots of trees. Based on the fact that Aktautitan had short legs, and its fossils are found in the lake sediments, this may be evidence of semi-aquatic way of life.



Dinoceratans (Dinocerata)
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1. Gobiatherium  2. Uintatherium  3. Eobasileus  4. Dinoceras 5. Tetheopsis
Among the most impressive looking of all Tertiary animals, the Dinocerata ("terrible horns") were a disitinctive group of rhinoceros-like hoofed herbivores of uncertain phylogenetic relationships. Neither long lived nor particularilyu diverse or widespread, their claim to fame rests on the fact that not only were they the first giant animals to appear since the extinction of the dinosaurs, but they were also equipped with an array of awesome acutriments, fearsome-looking tusks and - in advanced forms, three pairs of knobby horns, and the smallest brain to body-weight ration of any mammal living or extinct.
Interestingly the Dinocerata, or Uintatheres as they are also called (the group contains a single family - Uintatheriidae - with less than a dozen, mostly monospecific, genera) were the first of a number of rhinoceras morphotypes. They were succeeded in the late Eocene by the even larger Brontotheres (Titanotheres) which in turn were replaced by true rhonos and, in Africa for a short period during the early Oligocene, the bizarre, twin-horned Arsinotheres. In each case we are looking at animals of several tonnes in weight, who when fully grown been large and powerful enough to easily resist any contemporary predator. Indeed, for many of these animals the horns were actually small and blunt; only the arsinotheres and several rhino lineages had horns that could have been used as weapons. As with sauropods and elephants, size alone offers a great selective advantage.
But despite their commanding presence, the uintatheres did not survive the end mid Eocene (at one time believed to be the end Eocene, until the stratigraphy was corrected) turnover. ,Perhaps they were too specialised as regards diet or behavior. Their sudden disappearance paved the way for the next radiation of giant herbivores, the brontotheres, who, despite their rhino-like appearance, were actually the overgrown cousins of early horses.



The largest dinoceratan was
Eobasileus
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Eobasileus cornutus ("crowned dawn-king") was a prehistoric species of dinocerate mammal.
Eobasileus was 4 metres (13 ft) long and stood 2.1 metres (6.9 ft) tall at the shoulder; and with a weight up to 4000 kg (8818 lbs) it was the largest uintathere. With three pairs of short blunt horns on top its skull and two tusks that pointed down from the upper jaw, Eobasileus looked remarkably similar to its close relative Uintatherium (which is why unsurprisingly it is a member of the Uintatheriidae).  Eobasileus was one of the largest animals in its habitat and when fully grown and probably did not have to worry too much about being attacked by the much smaller creodont predators of the time. Like Uintatherium, it had three pairs of blunt horns on its skull, possibly covered with skin like the ossicones of a giraffe. The frontal pair may have been composed of keratin, like the horn(s) of a rhinoceros. Eobasileus also had a pair of tusks which were shielded by bony protrusions of the lower jaw.


Uintatherium
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It was about the size of a rhinoceros. Despite its large size, it had a brain only about as large as an orange. Uintatherium ("Beast of the Uinta Mountains") is an extinct genus of herbivorous mammal that lived during the Eocene epoch; two species are currently recognized, U. anceps from the United States during the Early to Middle Eocene, and U. insperatus of Middle to Late Eocene China.Uintatherium went extinct about 37 million years ago, presumably due to climate change and competition with
perissodactyls, such as brontotheres and rhinos.
Uintatherium was a large browsing animal. With a length of about 4 m (13 ft), a height of 1.70 m (5.6 ft), and a weight up to 2.25 tons, they were similar to today"s rhinoceros both in size and in shape, although they are not closely related. Its legs were robust to sustain the weight of the animal and were equipped with claws. Moreover, unlike the rhinos today , the sternum was made up of segments of Uintatheres horizontal planes, and compressed and vertical segments.
As with other early mammals of the Eocene epoch, Uintatherium didn"t exactly excel in the intelligence department, with an unusually small brain compared to the rest of its bulky body.
Its most unusual feature was the skull, which is both large and strongly built, but simultaneously flat and concave: this feature is rare and not regularly characteristic of any other known mammal except in some brontotheres. Its cranial cavity was exceptionally small due the walls of the cranium being exceedingly thick. The weight of the skull was mitigated by numerous sinuses permeating the walls of the cranium, like those in an elephant"s skull.
The large upper canine teeth might have served as formidable defensive weapons, and superficially resembled those of saber-toothed cats.
Sexually dimorphic, the teeth were larger in males than in females. However, they also might have used them to pluck the aquatic plants from marshes that seem to have comprised their diet.
The skulls of the males bore six prominent knob-like ossicones that grew from the frontal region of the skull. The function of these structures is unknown. They may have been of use in defense and/or sexual display.
Their fossils are the largest and most impressive of the finds at the excavation of Fort Bridger in Wyoming, and were a focal point of the Bone Wars between Othniel Charles Marsh and Edward Drinker Cope.
Fossils of U. anceps have been found in the Bridger and Wakashie rock formations, in the states of Wyoming and Utah near the Uinta Mountains, which are commemorated in the generic name. An almost intact skull of U. insperatus was found in the lower part of the Lushi Formation of the Lushi Basin in Henan Province, China.
A cast of a Uintatherium skeleton is on display at the Utah Field House of Natural History State Park. The skeleton of Uintatherium is also on display at the Smithsonian National Museum of Natural History in Washington, DC.
As the Eocene period continued, large brontotheres such as Megacerops and primitive rhinos like Metamynodon began to appear on the landscape. In time these similar herbivores seem to have displaced dinoceratans like Uintatherium from their ecological niche, as so far no remains of Uintatherium have been found in late Eocene deposits.














 




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Автор: valentint
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