It seems Mother Nature still has a few secrets up her sleeve.

In a study published in PLOS ONE this week, researchers announced the discovery of a new species of river dolphin in Brazil. The marine mammal is the first river dolphin to be described since 1918, the authors noted in the research.

Discovered in the Araguaia River basin, Inia araguaiaensis is believed to have diverged from river dolphins in the Amazon more than 2 million years ago due to a shift in the landscape. Unlike other river dolphins in Brazil, the newly discovered species has only 24 teeth per jaw, instead of the typical 25 to 29.

"It was something that was very unexpected, it is an area where people see them all the time, they are a large mammal, the thing is nobody really looked. It is very exciting," lead author Dr. Tomas Hrbek of the Federal University of Amazonas said, according to BBC News.

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However, despite the excitement behind the new discovery, it seems the river dolphins are already under threat of extinction.

"Its future is pretty bleak," Hrbek told the New Scientist. "The Araguaia-Tocantins basin suffers huge human disturbance and there are probably less than 1,000 I. araguaiaensis in existence."

Because of the small number remaining, the team is urging the International Union for Conservation of Nature to classify the species as vulnerable.

River dolphins are relatively rare. Of the four river dolphin species currently recognized, three are classified from vulnerable to critically endangered by IUCN. (There is not enough data to classify the fourth.)