Most likely, a new dolphin species was discovered in the Araguaia River Basin in central Brazil (east of the Amazon River), National Geographic reported. Scientists who located the mammal made their case for new species status in a study published Wednesday in the highly cited journal, PLOS One.

If it is indeed the fifth species of river dolphin known to scientific men, it will be the first such discovery within river dolphins since 1918, according to Nat Geo. That year, researchers in China described the Lipotes vexillifer, which was since declared extinct in 2006.

Like three out of the other four river dolphin species, also known as "botos," the one in question (if given new species status) would be considered "threatened" according to the IUCN's standards.

According to the researchers who spent extensive time studying 120 of the estimated 600 members of the Araguaian boto population (as it is being called) and one dolphin they found dead, the species came into being around two million years ago. Its discovery adds necessary insight into the origin of river dolphins, or as Howard Rosenbaum, director of the Wildlife Conservation Society's Ocean Giants program, put it to Nat Geo, is "amazing because we're starting to get insights into how these animals become distinct species."

Rosenbaum, who wasn't involved in the study, said the scientists made "a strong case based on the data." Researchers found both genetic and physical evidence differentiating the Araguaina boto from other botos, including cranial variations and differences in the number of teeth.

To truly brand the Araguaina bota as a new species (and gain approval from the Society for Marine Mammalogy), researchers will probably need to analyze a few more specimens, likely dead versions, according to Rosenbaum. Reluctant to kill any of the dolphins, researchers were forced to rely on live samples and the dead one they found washed ashore.

Like other river dolphins, the Araguainas are threatened by habitat destruction and tangles with local fishermen.

"Since the 1960's the Araguaia River basin has been experiencing significant anthropogenic pressure via agricultural and ranching activities, and the construction of hydroelectric dams, all of which have had negative effects on many biotic and abiotic aspects of the functioning of the Araguaia River ecosystem," the study said.

Skull shots of the proposed new species, courtesy of PLOS One.