Scientists have discovered what they believe to be the largest penguin ever to have existed on Earth, which stood taller than the average human at over six foot.

The giant penguin, called Palaeeudyptes klekowskii, lived between 37 and 40 million years ago and weighed more than 18 stone.

The fossilised remains of the mega penguin were discovered by researchers from Argentina's La Plata Museum on Seymour Island, in the chain of 16 islands on the Antarctic Peninsula.

The team uncovered two gigantic fossils that reveal just how large the penguin was, according to New Scientist. From beak tip to toe, the bird would have stood more than two metres tall.

The ancient penguin dwarfs today's Emperor penguins, the largest living species, which reach heights of around 1.36m (four feet).

"This was a wonderful time for penguins, where 10 to 14 species lived together along the Antarctic coast," said researcher Carolina Acosta Hospitaleche, as reported by Russia Today.

Around 40 million years ago, Seymour Island was a warmer region with a climate similar to modern-day Tierra del Fuego, an archipelago off the southernmost tip of the South American mainland.

Experts have said the extinct penguin may have been better off in modern times thanks to its ability to thrive in warmer areas, compared to today's species. Some experts believe that Emperor penguins are on the decline because of a warmer climate near the poles, while other researchers believe they are simply retreating to where it is colder with thicker ice.

According to Hospitaleche, P. klekowski could have stayed underwater for 40 minutes, as larger penguins can stay submerged for longer, giving it more time to hunt fish.

Thousands of penguin bones have been found in the area and the most complete P. klekowskii skeleton – around 12 bones from the wings and feet of the animal – was unearthed earlier this year.

Two larger bones, a wing section and a tarsometatarsus (formed by the fusion of ankle and foot bones), were found recently. The estimated height of the prehistoric penguin was based on the 9.1cm length of the tarsometatarsus.

"It is the longest foot bone I've ever seen," Dan Ksepka, of the Bruce Museum in Connecticut, told the Independent. "This is definitely a big penguin."

He added that the estimate of the length is uncertain because giant penguins had skeletons of different proportions to modern penguins.

The study was published in the journal Geobios.