Representational image of cows.Creative commons

A recent study has suggested that cows may become the biggest mammal on Earth after studying the trend of extinction of large mammals following the spread of humans around the world from Africa that began thousands of years ago.

However, not all researchers agree with this study. Thomas Brooks, chief scientist of the International Union for Conservation of Nature (IUCN) told Reuters that other research shows that large animals such as elephants are more likely to benefit in protected areas than smaller ones.

Also, IUCN Red List mentions some wild mammals like African buffalo and the brown bear, roughly the size of a cow, as unendangered.

Moreover, the researchers at the University of New Mexico excluded the largest creature ever existed, the blue whale. The endangered marine animal's population have been rising after conservational efforts.

The research that claimed the emergence of cows as the biggest mammal, pointed out that the trend over 125,000 years shows humans targeted big species for meat, making huge animals like mammoths and glyptodont (a huge armoured mammal) go extinct.

"There is a very clear pattern of size-biased extinction that follows the migration of hominims out of Africa," lead author Felisa Smith told Reuters.

The researchers also said the mean body mass of land-based mammals in North America has shrunk to 7.6 kg (17 lbs) from 98.0 after humans arrived.

The study was published in the journal Science.

The study warns that if the trend continues, animals like elephants, giraffes and hippos would go extinct and cows, weighing about 900 kg (2,000 lbs), would become the largest mammal on Earth in a few hundred years.

On March 20, the last male northern white rhinoceros Sudan died leaving only two white rhino (Sudan's daughters) alive on the planet.

Rhinos are often killed for their horn which is used in some traditional Chinese medicines and crafts.