Tigers, elephants, rhinos.
What is the first thing that comes to our mind when we think of these animals?
Yes, all these are near to extinction.
Now, what is this 'extinction'?
When there are no more animals of a particular species left alive,that species is said to be extinct. In the distant past, several species of animals became extinct due to natural causes.
Change in the climate of a particular region, and the plants or animals on which the species lived could have died out because of the change in the weather.
One animal might have been destroyed by another that was stronger or faster.
Now, we can only find their fossils and bones in the museums.
But nowadays, the culprit is man.
Man kills animals for his own selfish purposes without giving a second thought on what he will have to face later. 
Some Extinct Animals

A mammoth is any of a number of an extinct genus of elephant, often with long curved tusks and, in northern species, a covering of long hair.
 Mammoths lived during the Pleistocene epoch from 1.6 million to about 10,000 years ago. The word mammoth comes from the Russian mamont.They dissapeared after the end of the last Ice Age.

The dodo (Raphus cucullatus) was a flightless bird endemic to the Indian Ocean island of
Mauritius.
As with many animals that have evolved in isolation from significant predators, the dodo was entirely fearless of people, and this, in combination with its flightlessness, made it easy prey for humans.

The last confirmed sighting of a dodo was in 1662, but there were contested sightings as late as 1674.

Dinosaurs are a diverse group of animals that were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period (about 230 million years ago) until the end of the Cretaceous (about 65 million years ago).

The extinction of most dinosaur species occurred during the Cretaceous-Tertiary extinction event. 

The fossil record indicates that birds evolved within theropod dinosaurs during the Jurrasic period. Some of them survived the Cretaceous–Tertiary extinction event, including the ancestors of all modern birds.

Consequently, in modern classification systems, birds are considered a type of dinosaur—the only group of which that has survived to the present day.

Some Animals With a Possibility of being Extinct

The tiger (Panthera tigris), a member of the Felidae family, is the largest of the four "big cats" in the genus Panthera Native to much of eastern and southern Asia, the tiger is an apex predator and an obligate carnivore.

 Aside from their great bulk and power, their most recognisable feature is a pattern of dark vertical stripes that overlays near-white to reddish-orange fur, with lighter underparts.

The most numerous tiger subspecies is the Bengal Tiger while the largest is the Siberian Tiger.

India is home to the world's largest population of tigers in the wild.

According to the World Wildlife Fund of the 3,500 tigers around the world, 1,400 are found in India.

However, a tiger census carried out in 2007, whose report was published on February 12, 2008, stated that the wild tiger population in India declined by 60% to approximately 1,411.

 It is noted in the report that the decrease of tiger population can be attributed directly to poaching.

 

The giant panda, or panda (Ailuropoda melanoleuca, literally meaning "black and white cat-foot") is a bear native to central-western and south western China.

It is easily recognized by its large, distinctive black patches around the eyes, over the ears, and across its round body. Though it belongs to the order Carnivora, the panda's diet is 99% bamboo.

The panda is a conservation reliant endangered species.

 A 2007 report shows 239 pandas living in captivity inside China and another 27 outside the country.Wild population estimates vary; one estimate shows that there are about 1,590 individuals living in the wild.

 

Dolphins are marine animals  that are closely related to whales and porpoises.There are almost forty species of dolphin in seventeen genera.

Dolphins are among the most intelligent animals, and their often friendly appearance and seemingly playful attitude have made them popular in human culture.

Some dolphin species face an uncertain future, especially some river dolphin species such as the Amazon river dolphin, and the Ganges and Yangtze river dolphin, which are critically or seriously endangered.

 A 2006 survey found no individuals of the Yangtze river dolphin , which now appears to be functionaly extinct.

Pesticides, heavy metal waste, fishing using drift and gill nets, offshore construction projects like wind farms, loud underwater noises are some reasons that contibute to the future extinction of the dolphin.

 

Personally,I feel that Wild Animals belong to the wild and not our homes. I hope we all and our future generation will be lucky enough to experience the thrill of seeing wildlife in its natural habitat and not through books, movies or museums.