Platypuses, those small, egg-laying mammals with venomous feet and an electro-sensitive beak used for sensing prey, are one of the most unique living creatures in the world.

They're so unique that when a team of researchers found a deposit of ancient teeth in Australian limestone they immediately knew the samples belonged to platypuses. One tooth, however, was exceptionally large and befitted a platypus bigger than scientists thought possible, according to National Geographic.

Based on just the one tooth, researchers proclaimed a new species of platypus, Obdurodon tharalkooschild. At an estimated length of three feet, the platypus projects to be the largest ever found and nearly three times as large as modern day platypuses, which measure around 15 inches or approximately the size of a house cat.

The animal inhabited the freshwaters of Australia about 5 to 15 million years ago, National Geographic reported. Whereas the modern day platypus loses its teeth by adulthood and relies on "pads" to chew soft invertebrates like crayfish, the Obdurodon tharalkooschild retains them and potentially uses its teeth to ingest larger prey like frogs and turtles. Their bigger diet may be one factor in their larger size, according to National Geographic.

With just four fossils from extinct species of platypuses ever found, scientists have a limited understanding of the animal's evolutionary path. Now that they've uncovered a fifth, they understand the ancestry of the platypus to be much more complicated than prior evidence indicated, according to National Geographic.

"Monotremes (platypuses and echidnas) are the last remnant of an ancient radiation of mammals unique to the southern continents," said Columbia University PHD candidate and lead author of the study, Rebecca Pian. "A new platypus species, even one that is highly incomplete, is a very important aid in developing understanding about these fascinating mammals."

Previous evolutionary models show a continuous downward trend in the size of the species (and the size of the teeth), with the oldest samples belonging to platypuses from over 60 million years ago, according to The Register.

Since this tooth came from the largest platypus ever discovered, and, at around 10 million years old, defies that trend, the species may be "part of a now-extinct side branch of the main platypus lineage," according to National Geographic.

"Discovery of this new species was a shock to us because prior to this, the fossil record suggested that the evolutionary tree of platypuses was relatively linear one," said Dr. Michael Archer of the University of New South Wales, a co-author of the study. "Now we realize that there were unanticipated side branches on this tree, some of which became gigantic."

Modern day platypus: