The origin and evolution of elephants
In taxonomy, elephants belong to the class Mammalia, order Proboscidea, and family Elephantidae. They are native to Africa and their ancestors range from approximately 55 million to 36 million people. In the late Eocene 2000 years ago, ancestral elephants appeared in Egypt, Sudan and other places. Its body size is about the same as that of a domestic pig, and its living habits are similar to those of a hippopotamus. The body structure is relatively primitive and not specialized. Large tusks and long trunks have not yet appeared. However, the second pair of incisors are already larger than the teeth on both sides, and there is a tendency to develop into large tusks. The trunk is also slightly longer than other animals. . About 30 million years ago in the late Oligocene Epoch, the ancestors of elephants developed along three directions, one was Deinophorus, the other was brachyjawed mastodon, and the third branch passed through long-jawed mastodon, saber-toothed elephant, etc. stages, and finally evolved into modern elephants.
Dinoxus did not have huge tusks, but its mandible had a pair of large downward-curved teeth. The crowns of the cheek teeth were composed of two pointed ridges. It is a special branch that differentiated from the original type of elephant. It once lived in Eurasia and Africa, emerged in the early Miocene, and continued until its extinction in the Pleistocene.
Mastodons are the direct descendants of the ancestral elephants. The first one to appear was the ancient mastodon distributed in Africa in the early Oligocene Epoch. Its body was twice as large as the ancestor of the elephant, and its upper incisors further developed into continuously growing, downward-curving tusks. The enamel layer is limited to the outside of the tooth. Molars have three transverse ridges, and all molars are used simultaneously, rather than growing and being used one after another.
Mastodonts include long-jawed mastodon and brachyjawed mastodon. The jaws of the long-jawed mastodon represented by the codon and the sertodon, especially the mandible, were relatively long, and the tips of the cheek teeth became blunt and mastodon-like. The jaws of the brachygnathic mastodon represented by the yokedont were short, and the cusps on the cheek teeth did not form obvious papillae shapes, but many small cusps were connected together to form "ridge-shaped teeth."
The proboscis was a proboscis between the long-jawed mastodon and primitive elephants. It was further developed from the mastodon. The number of deciduous teeth on the molars increased, and the number of deciduous teeth on the same horizontal row was increased. The mastoid processes are connected and develop into transverse ridges. Later, saber-toothed elephants appeared in the Pliocene and Pleistocene. Its body was huge, its limbs were very long, its skull was tall, its upper jaw had long and curved teeth, its lower jaw was short and toothless, and its molars were greatly elongated. There are many low transverse ridges on the crown of the tooth. my country's saber-toothed elephants appeared in the early Pliocene and were still widely distributed in the middle of the Pleistocene. Eight species have been discovered so far, including the famous early Pleistocene Stegodon sangii in Yushe, Shanxi, the Early Pleistocene Pre-Oriental Stegodon in Liucheng, Guangxi, the Middle Pleistocene Oriental Stegodon in the provinces south of the Yangtze River, and the The early Pleistocene Yellow River ancient elephant discovered in Heshui County, etc.
There are only two species of proboscis in existence, the African elephant and the Asian elephant, which inhabit the tropical areas of Asia and Africa respectively. They are the largest living animals on land and have very similar appearances, but there are also many differences in morphology, mainly in the following aspects: 1. African elephants are larger than Asian elephants; 2. African elephants have smaller triangular ears. It is more than twice as big as the square ears of Asian elephants, like two huge cattail fans; 3. The tusks of African elephants are also much longer than those of Asian elephants, and both male and female animals have tusks, while only male animals have tusks of Asian elephants. Ivory; 4. The African elephant's trunk has many and deep wrinkles, like a hose with sections, and there are two fingers on the end of the nose. The Asian elephant's nose is smoother and has a smooth nose. There is only one finger on the end; 5. The African elephant’s back collapses downward, while the Asian elephant’s back is slightly arched upward; 6. The African elephant’s head is flat, while the Asian elephant’s forehead has two raised bumps. , commonly known as wisdom tumor, with a concave middle; 7. The African elephant has 4 toes on its forelimbs and 3 hooves on its hind limbs, while the Asian elephant has 5 toes on its forelimbs and 4 toes on its hind limbs; 8. The position of the shoulders and hips of the African elephant The highest, while the head of the Asian elephant is the highest. Anatomically, the African elephant has 21 ribs and 26 tail vertebrae, while the Asian elephant has 19 ribs and 33 tail vertebrae. In terms of ecological habits, Asian elephants mainly live in forests or jungle environments, while African elephants mainly live in grasslands or savannas. In terms of evolution, African elephants are relatively primitive.