The biggest penguin fossil ever discovered

The fossilised remains of one of the world’s largest and earliest penguins have been uncovered in New Zealand. Found in boulders on a beach near Otago in 2016, the remains, which date back over 50 million years, have now been carefully exposed so that the stature of the original animal can be appreciated and studied properly. It was a giant that would have weighed in at a hefty 150 kilograms. One of the team behind the discovery, and what it can tell us about the origins of penguins and their subsequent evolution, is Daniel Field, from the Department of Earth Sciences at Cambridge University.

Daniel - What we're talking about here with this giant penguin are the remains of its humerus or its upper arm bone and penguin humeri are very distinctive. Of course, penguin's move in a very different way from most other birds. They use their wings to fly underwater. And that specialized mode of locomotion has resulted in the evolution of a very distinctive humerus with an offset shoulder connection. The humerus itself is flattened, unlike a round cross section, like you see in the wings of flying birds. And so there's really no mistaking the humerus of a penguin when you find one

Chris - And you're extrapolating from what you do have to work out what what you don't have would've looked like.

Daniel - Yeah, so much of the humerus is preserved, not the entire thing, but I'm a pretty average size male in this country. I'm not quite six feet tall. But the humerus of this gigantic penguin would've been about the same length as mine. Just to give you a sense of how big this bone is.

Chris - You don't weigh 150 kilos looking at you <laugh>.

Daniel - I don't, I weigh almost exactly half that.

Chris - But this thing must have been enormous then.

Daniel - This was an utterly enormous bird. We estimate that it's body mass would've been in the range of about 150 kilograms, or I'm from Canada as you can probably tell from my accent. So back home we'd say 350 pounds, an absolutely huge, huge bird.

Chris -
Why so big?

Daniel - Well, there are various ideas about why penguins achieved such an enormous body size range early in their evolutionary history. Some of the most compelling ideas have to do with heat retention. Of course, birds and penguins are warm-blooded animals, and the larger you are, the deeper you can dive, the more oxygen you can hold onto. And these penguin fossils come from southern New Zealand. They would've been diving into very, very cold water. And being very large bodied would have enabled these gigantic early penguins to have collected more food, to have retained heat more efficiently, and probably also to have dived for longer because they would've been able to retain oxygen longer too.

Chris - But penguins still do all of those things today. So why have they shrunk?

Daniel - Well, penguins achieved very, very large body sizes early in their evolutionary history. So this fossil is about 57 million years old. And enormous penguins persist in the fossil record until around 30, 25 or so million years ago.

Chris - Oh, that's significant because the earth was really hot then. 30 million years ago, the polar ice caps melted, it was really warm then.

Daniel - That's right.

Chris - Was it a case they shrunk because the temperature went up?

Daniel - I don't think that's the argument I go with. There are smaller body penguins around at the same time. The important factor here is that around 30, 25 or so million years ago, marine mammals that fall within the same general size range as these very large body penguins came on the scene. And so we think the disappearance of these enormous penguins may have had something to do with the evolution of marine mammals that may have outcompeted these gigantic penguins.

Chris - So are you saying they're seal food?

Daniel - Well, they wouldn't necessarily have been seal food, but they might have been competing for the same food resources. And not only competing for the same food resources, but potentially also the same places at breeding colonies on beaches. Because of course, animals like seals need to come ashore to have their pups and penguins of course need to come ashore to lay their eggs.

Chris - You are saying this is 57 million years back in time. Now that is a significant point because that's not that long in geological terms after the dinosaurs disappear. So how significant is the timing that suddenly these very large birds are on the scene?

Daniel - So you're absolutely right, Chris. The extinction of the giant dinosaurs took place, we've got pretty good dates for this now, right around 66.02 million years ago. And the fact that we find these enormous penguins so early in the aftermath of this extinction event, within 10 million years of this extinction event, tells us that birds, once they lose the ability to fly, have the evolutionary capacity to attain enormous body sizes very, very rapidly. So it tells us something fascinating about the maximum possible rate of body size evolution in these animals.

Chris - And would it have been the disappearance of the dinosaurs that meant they could get that big because they weren't turning into dinosaur food?

Daniel - Ah, well it didn't have to do specifically with the disappearance of the dinosaurs, I don't think. But of course at the same time as the dinosaurs, we have giant marine reptiles that would've occupied these macro predatory marine niches. And I suspect it was the simultaneous disappearance of these giant marine reptiles 66 million years ago that may have opened up available ecological niche space that these birds would've been able to move into.

Chris - Is New Zealand special here?

Daniel - Well, New Zealand is very special when it comes to the fossil record of giant flightless birds because moa come from New Zealand as well as these giant penguins. But for penguin evolution specifically, New Zealand is very important because the very oldest penguin fossils we've ever found, as well as a very diverse fossil penguin fauna, have been recovered from New Zealand sediments.

Chris - Would this argue then that New Zealand is possibly the origin of penguins?

Daniel - Well, we think New Zealand and Australia would've separated around 86 million years ago. So New Zealand was an isolated land mass 57 million years ago when this giant fossil Kumimanu was alive. But the evidence that we do have suggests indeed that penguins may well have originated in New Zealand.