If extinction continues at its current pace, scientists are warning that cows could become the largest mammals left on earth.

The 2,000-pound peaceful farm animals may end up the largest land dwellers left in "a few hundred" years thanks to a combination of hunting, poaching and carnivorous diets, according to a study published in the journal Science.

"The only time being big is bad is when humans are involved. We are efficient predators and have been for a really long time — so there's not a value judgment here — it's just what hominids did," professor of biology at the University of New Mexico and lead author of the study Felisa Smith told Mashable.

"Species that went extinct tended to be two to three times bigger than mammals that survived, a trend that was evident globally," the study noted, indicating that size and extinction rates were linked. Most mammals today are degrees smaller than mammals from thousands or millions of years ago.

"There is a very clear pattern of size-biased extinction that follows the migration of hominims out of Africa,” the study’s lead author, Ms Smith said

If the trend continues “the largest mammal on Earth in a few hundred years may well be a domestic cow at about 900kg”, the researchers wrote.

Ms Smith said that the notion that climate change may have caused the disappearance of creatures like the woolly mammoth, elephant-sized sloths, saber-toothed cats, and rhino is inaccurate. While shifting climates, like the dawn of the ice age, caused adaptations in animals it was not the primary cause of their extinction.

She explained that in the past when an animal’s habitat was no longer suitable due to climate, it could simply move. But, humans eventually started getting in the way as people settled and developed.

Tragic moment rhino calf tries to suckle his poached mum

Her team of researchers looked into every continent in one million year intervals, over the last 65 million years of fossil data. Ms Smith said the impact of humans moving around and out of the African continent around 125,000 years ago was “striking”.

If the trend continues, “the average weight of mammals would also plummet to less than six pounds — roughly the size of a Yorkshire terrier,” USA Today reported.

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The study also found that 125,000 years ago, mammals were already 50 per cent smaller there than mammals on other continents, where humans had not made their way as yet. "We suspect this means that archaic humans and other hominins had already influenced mammal diversity and body size," co-author Kate Lyons of the University of Nebraska-Lincoln told USA Today.

In North America, for instance, the mean body mass of land-based mammals has shrunk to 7.6kg (17lb) from 98kg after humans arrived.