Extinct Animals

An animal is considered extinct when the last remaining member of its species dies out and there is not a single individual left on Earth.

Extinct animals are species that don't have a single living member left, either in the wild or in captivity.

When a large number of species goes out of existence in some major calamity, it is called an extinction event.

                     CAUSES OF EXTINCTION

                            Asteroid Strikes

This is the first thing most people associate with the word "extinction," and not without reason, since we all know that a meteor impact on the Yucatán Peninsula in Mexico caused the disappearance of the dinosaurs 65 million years ago. 

                            Climate Change

Even in the absence of major asteroid or comet impacts—which can potentially lower worldwide temperatures by 20 or 30 degrees Fahrenheit—climate change poses a constant danger to terrestrial animals. You need to look no further than the end of the last Ice Age, about 11,000 years ago, when various megafauna mammals were unable to adapt to quickly warming temperatures.

                                    Disease

While it's unusual for disease alone to wipe out a given species—the groundwork has to be laid first by starvation, loss of habitat, and/or lack of genetic diversity—the introduction of a particularly lethal virus or bacterium at an inopportune moment can wreak havoc. 

Witness the crisis currently facing the world's amphibians, which are falling prey to chytridiomycosis, a fungal infection that ravages the skin of frogs, toads, and salamanders, and causes death within a few weeks, not to mention the Black Death that wiped out a third of Europe's population during the Middle Ages.

                                Pollution

Marine life such as fish, seals, coral, and crustaceans can be exquisitely sensitive to traces of toxic chemicals in lakes, oceans, and rivers—and drastic changes in oxygen levels, caused by industrial pollution, can suffocate entire populations.

                            Loss of Habitat

Most animals require a certain amount of territory in which they can hunt and forage, breed, and raise their young, and (when necessary) expand their population. A single bird may be content with the high branch of a tree, while large predatory mammals (like Bengal tigers) measure their domains in square miles. As human civilization expands relentlessly into the wild, these natural habitats diminish in scope—and their restricted and dwindling populations are more susceptible to other extinction pressures.

                    Lack of Genetic Diversity

If genetic diversity gets too low, species can go extinct and be lost forever. This is due to the combined effects of inbreeding depression and failure to adapt to change. In such cases, the introduction of new alleles can save a population. This is called genetic rescue.