A new fossil discovery has revealed that New Zealand’s ancient monster penguins were not the only human-sized flightless birds that roamed our planet tens of millions of years ago.
Recent findings in North America and Japan suggest that giant creatures like penguins also spread throughout the northern hemisphere. And these birds may have been even bigger.
The strange thing is that the now-extinct group of birds, known as plotopterids, is unrelated to penguins, but they look remarkably similar, and likely used their fin-like wings in similar ways.
The earliest ancestors of penguins first appeared just over 60 million years ago around what is now New Zealand. Plotopterids developed in the northern hemisphere much later than their southern counterparts, only appearing between 37 and 34 million years ago and completely disappearing 10 million years later.
“These birds evolved in different hemispheres, millions of years apart, but from a distance it would be difficult to tell them apart,” says zoologist Paul Scofield, curator of the Canterbury Museum.
“The plotopterids looked like penguins, they swam like penguins, they probably ate like penguins, but they weren’t penguins.”
In a fascinating twist, this group of ancient flightless birds is more closely related to today’s very well-flying birds – fools, gannets, and cormorants. In recent years, we have come to understand much more about plotopterids, but this is the first time that their anatomy has been compared in detail to ancient penguins.
Analyzing the fossilized remains of 16 individual plopterids along with five representatives of three ancient penguin species, the researchers found many striking similarities along with some considerable differences.
Both plotopteridae and ancient penguins had long beaks embedded with slit-shaped nostrils, comparable chest and shoulder bones, and similar wings. But while some ancient penguins rose to 1.8 meters (6 feet), the largest plotopteridae were more than 2 meters tall.
It’s hard to imagine a bird, bigger than a human, diving into the water, but it seems like it was once a reality in both the northern and southern hemispheres.
(Mayr / Senckenberg Research Institute)
Above: Artist’s rendering of Kumimanu biceae, an extinct giant penguin, alongside a human diver.
Despite the fact that plotopterids have large webbed legs like penguins, the authors believe that they probably swam underwater relying primarily on their wing-like wings, judging by their anatomy.
“Wing-powered diving is quite rare among birds; most birds that swim use their feet,” says ornithologist Gerald Mayr of the Senckenberg Research Institute and the Frankfurt Museum of Natural History.
“We believe that both penguins and plotopteridae had flying ancestors that would jump from the air into the water in search of food. Over time, these ancestral species improved in swimming and worsened in flight.”
The fact that this happened in distantly related organisms, millions of years apart and on opposite sides of the world, is truly remarkable. It is a case of what scientists call ‘convergent evolution’, where similar traits develop in different species under similar environmental conditions.
Anatomical comparison of plotopterids and ancient giant penguins. (Mayr et al., Journal of Zoological Systems, 2020)
In this case, two separate groups of flightless birds developed the anatomy they would need to search for food deeper and deeper underwater. It just turned out to be remarkably similar.
“Therefore, we hypothesized that plotopterids and penguins had ancestors who did aerial dives to dive into the water and reduce energy costs to reach greater depths,” the authors write.
We will need more digs to discover why one lineage of these remarkable birds survived, while the other was forgotten.
The study was published in the Journal of Zoological Systematics and Evolutionary Research.
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