Wolf-sized prehistoric otter: You really oughter check out this critter

Otters, the fuzzy, playful sea mammals of internet fame, may not have been quite as cute 6.2 million years ago. 

Fossils recently unearthed by scientists reveal an ancient wolf-size otter species, known as Siamogale melilutra, that lived in rivers and lakes in a wetland region of southwestern China. It weighed about 110 pounds and measured up to 6.5 feet long, researchers say, dwarfing all of its modern relatives. 

S. melilutra is part of an ancient lineage of extinct otters that were previously identified only from isolated teeth belonging to another species, which were found in Thailand. But scientists were able to recover a mostly complete cranium, mandible, dentition and various skeletal elements, providing researchers with an opportunity to learn more about the taxonomy, evolutionary history, and functional morphology of the newly discovered species.

"Why did this species grow so large?" Denise Su, a curator and head of paleobotany and paleoecology at the Cleveland Museum of Natural History, said in a news release. "How did its size affect its movement on land and in water? And most importantly, what types of advantages did its size give?" 

One defining feature of S. melilutra was its big, strong jaw, thought to have been used to crunch large shellfish or freshwater mollusks, according to the authors of the study, which was published in The Journal of Systematic Palaeontology.

"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," Xiaoming Wang, the head of vertebrate paleontology at the Natural History Museum of Los Angeles County, told Reuters. "If Siamogale melilutra was not smart enough to figure out tools, perhaps the only option left was to develop more powerful jaws by increasing body size." 

Also notable are its enlarged teeth with rounded cusps, which resemble the teeth found in many otter lineages. Were these rounded-cusped teeth, known as bunodont teeth, inherited by all otters from a common ancestor? Or did they evolve independently in different otter lineages over time as a result of a phenomenon known as "convergent evolution," the evolution of similar adaptations to succeed in similar environments? 

Dr. Wang and Dr. Su believe the S. melilutra's teeth can be attributed to convergent evolution, as they found that bunodont teeth independently appeared at least three times over the evolutionary history of otters. 

Going forward, researchers say they hope studying the S. meliutra will continue to provide them with new insights into the evolutionary history of otters. 

"Siamogale melilutra reminds us, I think, of the diversity of life in the past and how many more questions there are still to answer," Su told Reuters. "Who would have imagined a wolf-size otter?" 

Despite its impressive size, S. melilutra may not be the largest known otter in history: that title, for the moment, could belongs to another ancient otter whose fossils were previously found in Africa, Reuters reports.

This report contains material from Reuters.