Moreover, the new findings suggest that S. melilutra belongs to one of the oldest and most primitive otter lineages, one that goes back at least 18 million years, to the European, badger-like animal Paralutra, the researchers said.
It's unclear why S. melilutra was so big, the researchers said. Usually, when carnivores evolve to be large, it's so that they have the strength to subdue prey, Wang said.
"But in our fossil otter, it is more likely a mollusk eater, and its powerful skull and jaws may be designed to crack tough shells of clams," he said.
Wang noted that modern sea otters also crack mollusks. But in addition to using their powerful teeth, these modern species also use tools - that is, rocks - to smash open the shells. [10 Animals That Use Tools]
"Perhaps our fossil otter had not learned to use rocks, and instead [would] apply brute strength to crush hard shells," Wang said.
This question is just one of many that researchers have about S. melilutra, said study co-researcher Denise Su, a curator at the Cleveland Museum of Natural History.
"We are working to answer questions regarding its paleobiology, like, 'How did it swim? How did it move on the ground? Why is it so large?'"
The study was published online today (Jan. 23) in the Journal of Systematic Paleontology.
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