Elephant Evolution

Introduction to Elephant Evolution:

African and Indian Elephants are the only proboscideans (Order Proboscidea) alive today, but there is a vast number of different species in the order that are now extinct. There are also many cases of parallel and convergent evolution. The closest living relatives of the modern-day elephant are in fact the dassie, or hyrax, and sea cows: manatees and dugongs. Sea cows and dassies are thought to have evolved from a common ancestor to the Proboscidae.

The earliest known ancestors to the elephant were herbivores that lived about 40 million years ago, and were roughly the sizes of pigs and cows. The direct ancestor to the modern-day elephant is unknown, but fossils of numerous evolutionary off-shoots, such as the moerithenes (40 million years ago), the barythenes (40 to 35 million years ago), paleomastodons (40 million years ago), gomphotheres such as the mastodon, the stegodon, and the mammoth have all been found and studied.

Gomphothere

There is still debate about which groups were early proboscideans, as other groups such as anthracobunids (55 million years ago) are considered by some to be the ancestors of moeritheres and sirenians (sea cows), but fossils are being discovered on an on-going basis, and the search for the proboscidian ancestor continues.

Most of our knowledge of these animals is based on the teeth, as these are not only durable, but very characteristic in these particular animals. (Elephant have unique teeth, and are known as 'lophodont': their teeth are huge, made up of a stack of enamel ridges, and move forward in the mouth like a conveyor belt as others are worn away.) Information has also been derived from skulls, entire skeletons, and, occasionally, a complete body preserved in ice.

The moerithenes were an evolutionary side-branch, were about 1 m tall, and were probably amphibious, eating aquatic plants. Small tusks were present in the lower jaw. Barytheres are also thought to be a side-branch: they had two pairs of tusks in both the upper and lower jaw, were lophodont (had the ridges on their teeth which form grinding surfaces), and had other similarities to modern-day elephants.

The deinotheres were undoubtedly proboscideans, and were a very successful group, as they lasted from about 24 million years ago to just 2 million years ago, and were widespread in Europe, Asia and Africa. They had lophodont teeth and large downwardly curved tusks in the lower jaws; the skulls found also indicate that it is likely that they had a trunk, although it may have been shorter than that of elephants. The name deinothere is based on the greek for 'terrible beast', as 19th century naturalists believed that it was a sea monster.

Paleomastodons lived about 40 million years ago in north Africa, and had many dental similarities with modern elephants. There were also other groups of ancient proboscideans that evolved and radiated out during the same time period, all with slightly different dental arrangements, including that of the tusks: a lot of these divergent forms have been labelled 'gomphotheres'. These animals evolved in different directions: some had elongated lower jaws while others had shortened lower jaws: it is thought that they inhabited different habitats, and that some forms were specialised for living and eating in swampy regions.

One of the more well-known members of the short-jawed gomphotheres is the mastodon, Mammut americanum. The mastodon had very long, strongly curved upper tusks, many of which have been found carefully preserved, along with entire skeletons. Mastodons were prehistoric elephant-like mammals, but are not part of the same family as elephants and the mammoth, as they are an earlier off-shoot of the evolutionary tree. Another well-known gomphothere is Platybelodon, which had broad, flattened shovel-like tusks protruding from its lower jaw.

Another off-shoot of the elephant evolutionary tree are the stegodontids, as they were also too highly specialised to be the ancestors of elephants. Many transitional forms have been discovered between early gomphothere species and elephants, which points to gamphotheres, and not stegodontids as was originally thought, as holding the key to elephant evolution.

Throughout the confusion of all these various forms and species, certain general trends in elephant evolution are apparent. There has been a general increase in size throughout, as well as a lengthening of the limb bones, the development of short, broad feet, an increase in skull size, elongation of the lower jaw, the development of the proboscis, or trunk, the reduction in the number of teeth (virtually every form has less and less teeth), and the excess growth of the second incisors to form tusks. The teeth have also become increasingly specialised to better enable the chewing and grinding of plants.

When the family Elephantidae was established, there were only three elephant species known: the African elephant, the Indian elephant, and the mammoth. After further fossils were found, and as more detailed investigation of fossils is now possible due to modern technology, this family is now known to include six genera and 26 elephant species, of which the African elephant and the Indian elephant are the only living representatives: these two species are the end result of over 50 million years of evolution. The African elephant is the largest living land mammal: some advantages of its great size are a lack of predators, as well as reduced heat loss. The African elephant is believed to have migrated throughout Africa, but remained on the continent, whereas the Indian elephant evolved in Africa and then later migrated to Eurasia.

The Indian elephant is actually more closely related to the now-extinct mammoth, genus Mammuthus, than it is to the African elephant. An interesting question is why the two elephant species are extant (ie: survived to the present day) while all the others become extinct. One reason is that they possessed both specialised and general characteristics, which enabled their lineages to adapt to an ever-changing environment, unlike the mammoth which was too highly specialised. One of the more commonly known mammoths, the woolly mammoth, survived until the end of the Ice Age, about 10 000 years ago, and was known to primitive man, as evidenced by the many drawings on caves and walls in Europe. It is unknown what caused the extinction of mammoths, mastodons and others at the end of the Ice Age, but climatic changes are likely to have played a part, as well as competition from species with similar ecological niches, and hunting by man: they were a source of food, clothing and dwelling material, and many bones have been found with charring, embedded projectile objects, and butcher marks. In spite of this, it is likely that man's influence was relatively small, and that the major cause of extinction was overspecialization.

• Introduction to Elephants • The African Elephant •

Best places to see the African Elephant in Southern Africa: