Потребителски вход

Запомни ме | Регистрация
Постинг
18.12.2015 16:39 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part1 Mammals ch. ch.14 Giraffids,Tapirids and Equines
Автор: valentint Категория: Забавление   
Прочетен: 3376 Коментари: 0 Гласове:
0

Последна промяна: 02.03.2019 18:30


Giraffids (Giraffidae) image

The giraffids evolved from a group of even-toed ungulates in the early Miocene almost 25 million years ago. They formed part of a relatively late mammal diversification that also produced cattle, antelopes, and deer following a climate change that transformed subtropical woodlands into open savannah grasslands. The giraffids diversified into many now extinct forms that inhabited large parts of Eurasia and eventually spread into Africa, where the only still extant forms persist. The most primitive forms had short necks and were about the size of a modern red deer, somewhat similar to the modern okapi.
The two main groups of extinct giraffids are: one group with robust limb bones, the Sivatheriinae, represented by Sivatherium during the Plio-Pleistocene, and another with long, slender limb bones classified in different subfamilies; either Giraffinae and Palaeotraginae or just Giraffinae (with the two tribes, Giraffini and Palaeotragini). While Giraffa and Palaeotragus can be easily attributed to the latter group, the placement of Okapia and Mitilanotherium remains disputed.Their closest fossil relatives include the deer-like palaeomerycids and the climacocerids, many genera of the latter having once been identified as giraffes themselves.
image

Fossil records indicate that many other giraffids thrived between the Miocene era (around 20 million years ago) and the recent past. One major group of extinct giraffids, the sivatheres, had enormous, branching ossicones, and would have looked more like massive deer than giraffes.



Sivatherium giganteum

image
Sivatherium giganteum is an extinct giraffid from the Plio–Pleistocene boundary of the Himalayan foothills. To date, there has been no rigorous skeletal reconstruction of this unusual mammal. Historical and contemporary accounts anecdotally state that Sivatherium rivalled the African elephant in terms of its body mass, but this statement has never been tested. Here, we present a three-dimensional composite skeletal reconstruction and calculate a representative body mass estimate for this species using a volumetric method. We find that the estimated adult body mass of 1246 kg (900—1912 kg range) does not approach that of an African elephant, but confirms that Sivatherium was certainly a large giraffid, and may have been the largest ruminant mammal that has ever existed. We contrast this volumetric estimate with a bivariate scaling estimate derived from Sivatherium"s humeral circumference and find that there is a discrepancy between the two. The difference implies that the humeral circumference of Sivatherium is greater than expected for an animal of this size, and we speculate this may be linked to a cranial shift in centre of mass.

image
Initially thought to be some form of elephant and later an antelope, the correct identification of Sivatherium as a giraffe did not come about until Geoffroy Saint-Hilaire identified it as one. However this theory was not universally accepted until close analysis found that the skull horns would have been covered by skin like in giraffes, and not keratin like in antelopes. The skull ornamentation of Sivatherium is composed of two small ossicones (similar to those of a giraffe) that are above the eyes, and two larger horns that rise up from the back of the skull. It is these two horns that have given rise to the term ‘moose-like’ which is often applied to Sivatherium.
Moose-like has also sometimes been used to describe the general build of Sivatherium which has also has a strong build around the shoulders on a body that is supported by long relatively thin legs. Sivatherium likely had powerful neck muscles that supported and stabilised the head from the additional weight to the horns on top of it. This form may seem bizarre to us today, but many prehistoric giraffes had similar body proportions to Sivatherium and today the closest living animal in form is the okapi (Okapia johnstoni), another conservatively proportioned giraffe from central Africa.
Back in the early days of is discovery Sivatherium was once considered to have had a specialised soft tissue development around the mouth like a trunk or extended movable lip that would help it to reach and scoop up food from the ground. Today in light of the fact that we know Sivatherium to have been a giraffe this is highly unlikely for two reasons. First is that giraffes carry their heads high so that they can reach to feed from trees, something that reduces competition between them and other herbivores that can only feed from lower down. Second is that giraffes today have long prehensile tongues that they can wrap around branches to strip off surprisingly large amounts of vegetation. Although so far not known for certain, it would be reasonable to think that Sivatherium as well as many other prehistoric giraffes had similar tongues adapted for this way of feeding.


Equines (Equidae)
image

Equidae is a family of odd-toed ungulate mammals of horses and horse-like animals. It is sometimes known as the horse family. All extant equids are in the genus Equus and include the three basic groups of horses, asses, and zebras. There are eight to ten extant species in Equidae, depending on the taxonomic scheme.
The oldest known equid fossils date from the early Eocene, 54 to 55 million years ago. This species, Hyracotherium (formerly known as Eohippus) but the type species of that genus now is regarded to be not a member of this family. The other species have been split off into different genera. These early Equidae were fox-sized animal with three toes on its hind feet, and four on the front feet. It was herbivorous browser on relatively soft plants, and already adapted for running. The complexity of its brain suggests that it was already an alert and intelligent animal (Palmer 1999). Later species had less toes and teeth more suited for grinding up grasses and other tough plant food.
The genus Equus, which includes all extant equines, is believed to have evolved from Dinohippus, via the intermediate form Plesippus. One of the oldest species is Equus simplicidens, described as zebra-like with a donkey-like head shape. The oldest material to date was found in Idaho, USA. The genus appears to have spread quickly into the Old World, with the similarly aged E. livenzovensis documented from western Europe and Russia.
image
Molecular phylogenies indicate that the most recent common ancestor of all modern equines (members of the genus Equus) lived ~5.6 (3.9-7.8) Mya. Direct paleogenomic sequencing of a 700,000-year-old middle Pleistocene horse metapodial bone from Canada implies a more recent 4.07 Mya for the most recent common ancestor within the range of 4.0 to 4.5 Mya.

Mitochondrial evidence supports the division of Equus species into noncaballoid (which includes zebras and asses) and caballoids or "true horses" (which includes E. ferus and E. przewalskii).Of the extant equine species, the lineage of the asses may have diverged first,possibly as soon as Equus reached the Old World.Zebras appear to be monophyletic and differentiated in Africa, where they are endemic.
Molecular dating indicates the caballoid lineage diverged from the noncaballoids 4 Mya.Genetic results suggest that all North American fossils of caballine equines, as well as South American fossils traditionally placed in the subgenus E. (Amerhippus), belong to E. ferus.Remains attributed to a variety of species and lumped together as New World stilt-legged horses (including E. francisci, E. tau, and E. quinni) probably all belong to a second species that was endemic to North America.The possible causes of the extinction of horses in the Americas (about 12,000 years ago) have been a matter of debate. Hypotheses include climate change and overexploitation by newly arrived humans.Horses only returned to the American mainland with the arrival of the conquistadores in 1519.
The Equidae group became relatively large during the Miocene, with many new species appearing. By this time, equids were more truly horse-like, having developed the typical body shape of the modern animals. Many of these species bore the main weight of their bodies on their central, third, toe, with the others becoming reduced, and barely touching the ground, if at all. The surviving modern genus, Equus, had arisen by the early Pleistocene, and spread rapidly though the world.


Equus giganteus
image
This giant ice age horse was extremely large and powerful, reaching up to 2 m (6.5") tall at the shoulders. It was possibly the largest species of horse to have existed, comperable to the Percheron and Shire horse, but more agile. The head was proportionally larger than a modern horses. The mouth was endowed with large, strong teeth, capable of chewing tough vegitation or seriously damaging predators. The legs were long, and built for both power and agility with hard hooves. It seems Equus giganteus had a rather thicker coat than a modern horse.
Equus giganteus would have spent a lot of time searching out edible grasses, possibly being nomadic. This species of horse would have shared it"s range with a veriaty of predators, but it would have been quick on the escape, and extremely powerful in a fight, able to generate extreme force with a kick or bite.
This horse"s dentition indicates a diet of grasses, which would seem to indicate a plains dweller. It"s fossils have been found in the eastern United States.

Tapiroidea
image

1. Protapirus 2. Miotapirus  3. Megatapirus  4. Heptodon 5. Amynodon
Tapiroidea is a superfamily of perissodactyls which includes the modern tapir. Members of the superfamily are small to large browsing mammals, roughly pig-like in shape, with short, prehensile snouts. Their closest relatives are the other odd-toed ungulates, including horses and rhinoceroses. Taxonomically, they are placed in suborder Ceratomorpha along with the rhino superfamily, Rhinocerotoidea. The first members of Tapiroidea appeared during the Early Eocene, 55 million years ago.

The first tapirids, such as Heptodon, appeared in the early Eocene.They appeared very similar to modern forms, but were about half the size, and lack the proboscis. The first true tapirs, appeared in the Oligocene, and by the Miocene, such genera as Miotapirus were almost indistinguishable to the extant species. It is believed that Asian and American tapirs diverged around 20 to 30 million years ago, and that tapirs migrated from North America and Central America into South America around 3 million years ago, as part of the Great American Interchange.For much of their history, tapirs were spread across the northern hemisphere, where they became extinct as recently as 10,000 years ago.


Giant tapir (Megatapirus augustus)
image
Giant 
tapir ( Megatapirus augustus) is an extinct tapir that lived in southern China and Vietnam. It appeared during the Middle Pleistocene and survived until about 4,000 years ago in China. It was larger than modern tapirs, being 2.5 metres (7.9 ft) long and 1.20 metres (4.0 ft) tall at the shoulders, and may have weighed up to 600 kilograms (1,400 lb).
Matthew and Granger originally named Megatapirus augustus as a subgenus of Tapirus. Hurlbert synonymized it with Tapirus. Based on these sources,Tapirus augustus is known primarily from Middle-Late Pleistocene Yanjinggou fauna (formerly anglicized as “Yenchingkou”) of Sichuan province, southern China. Additional specimens of T. augustus have been reported from Java, Vietnam, and Laos. All of these localities belong to the Pleistocene “Stegodon-Ailuropoda faunas” of Southeast Asia.







 

 




Гласувай:
0
0



Няма коментари
Търсене

За този блог
Автор: valentint
Категория: Политика
Прочетен: 922435
Постинги: 225
Коментари: 18
Гласове: 16
Календар
«  Юли, 2020  
ПВСЧПСН
12345
6789101112
13141516171819
20212223242526
2728293031