Fossils Of Prehistoric Giant Otter In China Hint Of Convergent Evolution

Wolf-sized giant otters that weighed more than 100 pounds lived among birds and water lilies in prehistoric China more than 6 million years ago.

Otter evolution is not well understood as fossils of the creature are rare and scattered worldwide. The discovery of an ancient species of a large otter in China, though, offers researchers some insights about these animals.

Giant Otter Siamogale Melilutra Up To Thrice The Size Of Modern-Day Otter

In 2010, researchers discovered a well-preserved cranium of the now-extinct species of giant otter dubbed Siamogale melilutra in an open lignite mine in Yunnan province in China. The fossils also include various teeth, limb bones, and lower jaw of the creature.

Denise Su, from the Cleveland Museum of Natural History, and colleagues who published their findings in the Journal of Systematic Paleontology on Jan. 22, described the prehistoric creature to be up to three times larger than any modern otter.

Almost Complete Cranium Reconstructed Through CT Scan

Su said that the fossilized cranium was almost complete albeit flattened to about an inch and a half thick. Because the bones are fragile, researchers were not able to reconstruct them physically. Su and colleagues decided to take CT scans of the cranium to digitally reconstruct it.

The cranium revealed that the creature had teeth with badger features and provided the researchers with crucial information on how otters evolved. The cranium also shed light on a dental mystery.

Convergent Evolution

Scientists wanted to know whether different species of otter inherited their teeth from a common ancestor or the teeth evolved separately since they were eating similar things, a process called convergent evolution.

By comparing the specimen of the prehistoric otter to modern and other fossil otters, the researchers found that the otters' bunodont teeth emerged because of convergent evolution and not because of inheritance from a common ancestor.

Strong Jaws For Crunching Hard Objects

The ancient creature also featured strong jaws that may have been used for crunching hard objects, possibly freshwater mollusks and large shellfish.

"I think it used its powerful jaws to crush hard clams for food, somewhat like modern sea otters, although the latter use stone tools to smash shells," said Xiaoming Wang, from the Natural History Museum of Los Angeles County.

Body Size To Support Development Of More Powerful Jaw

Wang said that if the creature was not smart enough to use tools, then the only option it likely had was to develop more powerful jaws by increasing its body size.

Despite its large size, the S. melilutra is not the largest otter that researchers have so far discovered. Fossils of a larger ancient otter have previously been found in Africa.

Badger Relatives

The biggest living otter is the South American giant river otter, which weighs up to 70 pounds. Otters belong to a family of mammals that include the badger, marten, mink, and the weasel.

Researchers said that studying the newly found prehistoric species of otter will provide them with new insights on how otters evolved.

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