The new species was described for the first time this week in the Journal of Systematic Paleontology, based on remains uncovered at Shuitangba, a fossil-rich mine in northern China.
Before this latest discovery, S. melilutra was known only by a few isolated teeth recovered in Thailand. Those scattered bits hinted at the impressiveness of this massive, furry creature. But they were not enough to identify it as a new species.
The new find included the creature's mandible, some teeth and limb bones, along with a complete cranium — a rarity in the fossil record.
“We were incredibly lucky to be able to find this,” co-author Denise Su, the curator of paleobotany and paleoecology at the Cleveland Museum of Natural History, said in a video produced by the museum.
The remains were squashed during the fossilization process, but researchers were able to CT scan the flattened fragments and reconstruct them virtually, revealing a member of one of the oldest and most primitive lineages in the otter family. Though it's definitely a member of the otter family (Lutrinae), its features resembled those of badgers (whose Latin name is melus), so the researchers smashed together the two Latin terms to get the species name “melilutra.”
At 110 pounds, S. melilutra was at least twice as big as the largest living otter species, the South American giant river otter, and four times as big as the North American river otter (i.e. Mrs. Otterton from the Disney movie “Zootopia”).
The species' teeth, the cusps of which have low, rounded “bunodonts” rather than sharp peaks, are like those of pigs, bears and humans. Several other otter lineages also have these rounded cusps, prompting Su and her colleagues to wonder whether this trait was inherited from a common ancestor. But analysis of their evolutionary family tree suggested that the presence of bunodont teeth in several otter species is a consequence of convergent evolution — different species independently evolving the same trait because they face similar environmental circumstances.
“The discovery of the otter helps solve some questions about otter relationships, but has opened the door to new questions,” Xiaoming Wang, curator and head of vertebrate paleontology at the Natural History Museum of Los Angeles County, said in a statement.
For example, Wang said, scientists still don't why S. melilutra grew so large relative to its modern cousins, how it moved on water and land, or how it ate. Clearly, they otter learn more.