Penguins are pretty darn cute. They chirp and waddle, and their chicks are more or less the definition of adorable. But there was once a penguin that you wouldn't want to run into in a dark alley — or a dark ice shelf.

Kumimanu biceae, described in the journal Nature Communications, stood almost 6 feet tall and weighed over 200 pounds. Understandably, the researchers took the Maori words for monster — "kumi" — and bird — "manu" — and put them together when naming this very large bird.

Giant water birds of prey

Sizable penguin species aren't a new discovery. We know of at least three species of penguins from 30 million years ago that stood at least 5 feet tall — Icadyptes salasi, Inkayacu paracasensis and Pachydyptes ponderosus — and just earlier this year, a penguin that stood about 5-and-a-half feet tall and thrived in New Zealand and Antarctica 40 million years ago was described for the first time.

These birds pale in comparison to the Palaeeudyptes klekowskii, an über penguin that may have stood over 6 feet tall. This height likely gave it a clear view of the then much warmer Antarctica of 37 to 40 million years ago. And considering its size, it was probably a fearsome underwater predator, likely having the ability to stay underwater for nearly an hour.

To put all these heights in perspective, the tallest extant species of penguin, the emperor penguin, only tops out at around 4 feet, while the smallest penguin, the little penguin, grows to be barely a foot tall.

K. biceae doesn't quite reach the considerable heights of the P. klekowskii, but it does easily tower over currently living penguins species and is on par with some other giant penguins. But it has something else that allows it stand apart from these other giant pinguinos: It's so old that it may very well be one of the first penguins ever.

The grandparent of giant penguins?

An illustration of the Kumimanu biceae and a human scuba diver An illustration of a Kumimanu biceae and a human diver shows the similar sizes between the two. (Photo: Gerald Mayr/Senckenberg Research Institute)

The fossilized remains of a K. biceae were discovered in the Otago region on New Zealand's South Island. The bones, mostly from wings, chest and legs, indicated a very large bird, and the age of the rock layers, between 60 and 65 million years, indicated a very old bird.

"The fossils are therefore among the oldest known penguin remains, and it is remarkable that even these early forms reached such an enormous size," Gerald Mayr of the Senckenberg Research Institute in Frankfurt, said in a statement.

Mayr and the other researchers compared the bones to some of the other ancient penguins to get a sense of similarities and sizes. What they found was that K. biceae had bone features somewhere in between its descendants and older penguins, like Waimanu, a "proto" penguin species discovered in New Zealand that is older (but much shorter) than K. biceae. Both of these birds likely represent the most primitive branches of the penguins' genetic family tree, with K. biceae being even farther apart from the giant penguins described above.

As for how and why penguins like K. biceae got so big, scientists aren't sure. Mayr speculated to The New York Times that the cause of their size was the extinction of dinosaurs and other marine creatures. After that, penguins had free reign of the ocean since their largest predators had all died.

No more giants

So what happened to these gigantic birds? The evolutionary steps that helped make them so big may have also resulted in their extinction.

As mammals turned to the ocean, they may have been able to beat the giant penguins for resources, including land for breeding. Or perhaps the penguins themselves became the resource.

"However, with the subsequent appearance of other large marine predators such as seals and toothed whales, the penguins faced new competition and predation — which may have led to their extinction," Mayr said in the statement.

Perhaps only smaller penguins were able to survive and continue to thrive and evolve into the penguins we're familiar with today.