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Elephant Evolution
Enter the world of the most majestic and inspiring of all animals, the elephants.
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Elephants, as commonly known, are the largest of all existing land animals. And if this isn't enough of a distinction, this amazing species is one of the most intelligent, sensitive, and compassionate of all creatures. Currently, there are only two existing species of elephants, the African elephant and the Asian elephant. These are the sole remaining descendents of a long line of elephant-related species. Nature has taken a long and remarkable journey in the course of evolving the elephants that we know today. However, as a species that is increasingly threatened with extinction, there lies the question of whether elelphants have the time to evolve any further.
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Order Proboscidea
Elephants and their ancestors belong to the order Proboscidea. Proboscidea means having a proboscis, or trunk. Over the course of evolutionary history, it has been estimated that there have been about 352 species of Probscideans. The creatures of this order have inhabitated every single continent except Australia and Antarctica. All but two (the African and Asian elephants ) have died. It has been hypothesized that Proboscideans were able to exist in so many environments because they were capable of specializing to particular habitats. This enabled them to disperse across the continents. However, this very advantage became a disadvantage in the face of radical changes in their habitats. Because of their specialization, they were unable to adapt and survive. Their general large sizes and the other problems associated with their enormous structure, proved to hinder their adaptive abilities.
The trend in the evolution of Proboscidea, has generally been an increase in size, relected in longer limb bones and larger skulls and teeth. As Proboscideans have grown taller, their trunks have grown longer. Because their heads are farther from the ground, nature has compenstated for this height by developing the trunk as a necessary tool. For such large animals, the trunk has provided a fast and convenient way of reaching food and water on the ground, instead of having to bend down and put themselves in a vulnerable position. A long trunk has enabled Proboscideans to investigate the ground and eat and drink, while still watching and listening for approaching danger. As a result, nature has selected in favor of longer trunks.
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Moeritherium
The earliest relatives of elephants, were the Moeritheriums. They lived about 50 million years ago. Moeritheriums were about the size of pigs and are supposedly best described as pygmy hippopotamuses. They didn't have trunks, but snouts that were probably the very beginnings of trunks. Another key feature that ties them to elephants, is their enlarged upper-jaw incisors. Elephants' tusks are massively enlarged incisors too. Fossils of Moeritherium were found at the El Faiyum oasis located near the Nile, which suggests that the roots of elephants began in Africa.
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Family Elephantidae
Out of the order Proboscidea, developed the family Elephantidae. Within this family, are the Asian elephant, African elephant, and the mammoth. Previous to these species however, were other closely related ancestors.
Trilophodon
This species lived about 26 million years ago and it was characterized by its four tusks. Two tusks curved upward out of the upper jaw, and two tusks curved downward out of the lower jaw.
Deinotherium
This creature had two downward curving tusks that were probably used in a shovel-like manner to scoop vegetation out of the watery swamps where it lived. It existed approximately 25 million years ago. They had no tusks in their upper jaw, making them somewhat unusal.
Platybelodon
This creature also had two lower flattened tusks again used for digging and scooping vegetation.
Mastadons
More correctly classified as part of the family Mammutidae, the remains of the first Mammutidae, descended from the paleomastodon, were found in 25 milllion-year-old Oligocene strata in Africa and Eurasia. These animals were about the size of today's elephants, but more solidly built with a hairy body.
Mammoth
Of the proper Elephantidae family, the mammoths were the first. An important evolutionary step was made in the creation of this family. This involved a change in the chewing teeth. The grinding surfaces of the molars formed into transverse ridges of dentine covered with hard enamel. The dips in between contained tooth cement, which was a softer material. This formation of the teeth, caused the parts to wear down at different rates, resulting in a constantly rough surface. This unevenness in the teeth, enabled the animals to eat tougher foods and thereby inhabit more barren habitats. The first mammoths lived in Africa about three million years ago. It wasn't until 120,000 years ago that the mammoths spread to cold regions too. The evolutionary development of the the woolly coat of the woolly mammoth, enabled it to live in the cold and snow.
Asian Elephant
At about the same time that the mammoth was coming into existence, so was the Asian elephant, under the genus Elephas. The proper name of the Asian elephant, is Elephas maximus. It also originated in Africa, and it is believed to have a stronger evolutionary tie to mammoths, than it has with African elephants, or that African elephants have with mammoths. Asian elephants spread throughout Eurasia, and they now exist in India, Sri Lanka, China, and South East Asia. Elephas maximus indicus is the Indian subspecies. Elephas maximus sumatranus is the subspecies of Sumatra. On the island of Sri Lanka, there is also a subspecies called Elephas maximus maximus. The isolation that the island has provided, has allowed a sort of divergent evolution to occur. Most of the bulls there are tuskless, though they are not a separate species. This may be the result of a selection process in which, over a period of centuries, bull wiht particularilylarge tusks were shot by ivory hunters, and had fewer offspring as a result. This is a sad, but interesting example of the role that humans can play in the evolution of other species.
African Elephant
The African elephant, Loxodonta africana, appeared about one and a half million years ago in Africa, making it the most recent elephant species. It differs from the Asian elephant in its larger size, larger ears, two-fingered trunk (as opposed to the Asian's one-fingered trunk), and the fact that both males and females have tusks (male Asian elephants have tusks but female's are very small if they have any at all). The largest of all elephants, is the the savanna or bush elephant, Loxodonta africana africana. There is also a much smaller forest elephant called Loxodonta african cyclotis. It inhabits the equatorial rain forests of West and Central Africa. They tend to have small, rounded ears and darker skin. Interbreeding occurs between the savanna and forest elephants in areas where the two habitats meet. At one time African elephants inhabited the whole of the African continent. Now they are found only south of the Sahara, due to shrinking habitat and the effects of man's presence (namely the ivory trade). Another interesting evolutionary feature of elephants that is particularily relevant to African elephants, is their infrasonic hearing and moaning. This ability to hear sound waves below our own hearing level, is a crucial means of communication for elephants out on the wide open plains. In this way, they can talk to each other without alerting predators to their position (the predators can't hear their communication). This convenient ability was naturally selected for because of the advantage it gave elephants.
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Pygmy Elephants
Despite the overall trend for elephants and their ancestors to have increased in size over time, there have been exceptions as demonstrated by the existence of pygmy elephants. Fossil evidence has been found that supports the belief that pygmy forms did exist in many parts of the world, especially islands (in the Mediterranean, Sicily, Malta, Crete, Cyprus, and Tilos).These creatures may have been isolated on island habitats and would have had to adapt to a restricted food supply and would have been subject to inbreeding. The last of these small pygmy elpephants died about 4,000 years ago, probably in response to climate changes, disease, and possibly human acts of extermination.
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The Zoo Generation
The recent International Convention on Species Protection, bans capture of elephants living in the wild and any trade in such animals. Therefore, it has become inherent that zoos establish their own breeding programs, as the wild animals will no longer be a source. Over the past few decades, elephant breeding has become decidedly more successful and has led to the development of a zoo generation of elephants. These elelphants are essentially pets, dependent upon human care. They grow up in captivity and are not considered wild animals. Because zoologist and keepers have a significant hand in determining which pairs of elephants breed, it will be interesting to see whether a zoo subspecies of elephant will develop. Because of the limited selection of captive elephants, inbreeding and other weaknesses are definite factors.
*For pictures on the evolution of the elephant and a comparison of the African and Asian elephant, click here.
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