Giant, wolf-sized otters used to roam around in China

Otters are one of the best animals on Earth. They're playful creatures that climb and slide down hills and wrestle with each other, they float on their backs and hold paws, and they use stones to bash open food like clams and mussels.

They're quite small creatures, but new research has shown this might not always have been the case.

There are 13 species of otter today of different sizes, and they live in various habitats; some in salt water and some in rivers. The largest of them all is the giant otter, which lives in South America and weighs up to 32 kg. 

However, researchers have uncovered fossils that show that the biggest ever otter was much larger than that. 

A new paper, published this week in the Journal of Systematic Palaeontology, explains how the scientists came to the conclusions about what this prehistoric otter looked like, which they called Siamogale melilutra, because of similarities both otters (lutra) and badgers (melis.) They examined limb bones and skull remains that were taken from carbon-rich rocks about a decade ago.

The skull was pretty crushed though, so the team used a CT scans to work out what the skull would have looked like, and a sophisticated computer program to digitally reconstruct it from 200 fragments.

They found that Siamogale melilutra's skull was 8 inches long. From this information they concluded the creature likely weighed around 50kg, which is about the size of a wolf, and roughly twice the size of today's giant otter. Carbon dating shows they lived around 6.2 million years ago in humid swamps which are now the Yunnan province in China.

Surprisingly, when the researchers looked at the shape of Siamogale melilutra's teeth, they concluded that they had evolved that way at least 3 separate times. So rather than all otters sharing a common ancestor, this prehistoric otter probably evolved along its own line, which is known as convergent evolution.

"The discovery of the otter helps solve some questions about otter relationships, but has opened the door to new questions," said Dr. Xiaoming Wang, Curator and Head of Vertebrate Palaeontology at the Natural History Museum of Los Angeles County and lead author of the paper, in a statement. "For instance, why was it so large, how did it crack open mollusks and shellfish for food, and how did it move in the water and on land?"

The team hope to fill in more pieces of the puzzle of the otter's prehistoric family tree with further research. 

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