The common belief is that extinction is a rare event, and the word brings dinosaurs to mind. But many animals around us are disappearing without our knowing.

According to an estimate by the World Wide Fund for Nature, a non-governmental organisation that works to protect wildlife, about 10,000 species become extinct every year. The organisation says, however, that people have no clear idea how many species are alive in nature today, which makes it hard to give an exact count of how many are going extinct.

Lost and extinct animals will be remembered around the world on 30 November. Before that, the report introduces some of the species that it describes as having vanished and come back.

This red-headed monkey went extinct around 2000. It lived on the border of Ghana and Ivory Coast. A feature of Miss Waldron's red colobus is that it has no thumbs.

It usually lived in groups in dense forest, so as the forests shrank its numbers began to fall. Because its breeding and reproduction were slower than those of other animals, it eventually disappeared.

This dolphin was declared extinct in 2006. The Yangtze river dolphin was pale and ash-grey, and not as striking to look at as other dolphins.

Source: BBC Bangla. First published in Bengali on The Agro News.