Los Angeles, Preventing extinction of large mammals, including gorillas, rhinoceroses, elephants, lions, tigers, wolves and bears, will require bold political action and financial commitments from nations worldwide, researchers have warned.

"The loss of these magnificent animals would be a tremendous tragedy. They are all that is left of a once much more diverse megafauna that populated the planet only 12,000 years ago," said Blaire Van Valkenburgh from University of California, Los Angeles (UCLA) in the US.

"And more importantly, we have only just begun to understand the important roles they play in maintaining healthy ecosystems," said Van Valkenburgh.

Among the most serious threats to endangered animals are illegal hunting, deforestation, habitat loss, expansion of livestock and agriculture into wildlife areas, and human population growth, according to researchers.

"Humans have an abiding moral obligation to protect the Earth's megafauna, or large mammals. We must not go quietly into this impoverished future," they said.

In addition to their significance to ecosystems, animals such as tigers and elephants attract tourists and their money to parts of the world that have few alternative sources of income, said Van Valkenburgh.

As many as 59 per cent of the largest carnivores and 60 per cent of the largest herbivores have been classified as threatened with extinction, and the situation is especially severe in sub-Saharan Africa and Southeast Asia, where the greatest diversity of extant megafauna live, researchers said.

According to William Ripple from Oregon State University in the US, the animals' declines are occurring rapidly.

"The more I look at the trends facing the world's largest terrestrial mammals, the more concerned I am we could lose these animals just as science is discovering how important they are to ecosystems and to the services they provide to people," he said.

Researchers call for comprehensive action, including expanding habitats for the animals and changing conservation policy.

According to them, some conservation initiatives have been successful and if measures are taken now, it may still be possible to rescue these animals from extinction. 

Preventing the extinction of gorillas, rhinoceroses, elephants, lions, tigers, wolves, bears and the world's other large mammals will require bold political action and financial commitments from nations worldwide, researchers said.

The findings were published in the journal BioScience.