Paleontologists have uncovered striking similarities between the fossilized bones of giant penguins that lived 62 million years ago in what is now New Zealand and those of plotopterids, a group of flightless seabirds that lived in North America and Japan between 37 and 25 millions of years ago.
A group of Copepteryx, plotopterid birds that lived in Japan between 28.4 and 23 million years ago. Image credit: Mark Witton.
The plotopéridos (family Plotopteridae) are extinct, flightless and wing-powered diving birds that combine a striking mosaic of characteristics characteristic of true penguins and pellecan-like birds such as gannets, boobies, cormorants and Anhingas.
The wing of the plotopteridos is remarkably similar to the fin of the penguins, to which it shows numerous parallels.
Plotopterids developed in the northern hemisphere much later than penguins, and the first species appeared between 37 and 34 million years ago. Their fossils have been found at various sites in the United States (California, Oregon, and Washington), Canada (British Columbia), and Japan.
Unlike penguins, which have survived into the modern era, the last species of plotopterid became extinct about 25 million years ago.
In a new study, Dr. Gerald Mayr of the Senckenberg Research Institute and the Museum of Natural History and his colleagues in the United States and New Zealand compared the fossilized remains of plotopterids with fossil specimens of three species of giant penguins: Waimanu, Muriwaimanuand Sequiwaimanu – and identified similarities and differences not previously recognized.
The researchers found that the plotopteridae and the ancient penguins had similar long beaks with indentation-shaped nostrils, similar bones in the chest and shoulders, and similar wings.
These similarities suggest that both groups of birds were strong swimmers who used their wings to propel them underwater in search of food.
Some species in both groups could grow to enormous sizes. The largest known plotopteridae were over 2m long, while some of the giant penguins were up to 1.6m tall.
“The surprising thing about all of this is that plotopterids and ancient penguins developed these shared characteristics independently,” said Dr. Vanesa De Pietri, curator of natural history at the Canterbury Museum.
“This is an example of what we call convergent evolution, when related distant organisms develop similar morphological features under similar environmental conditions.”
“Some large species of plotopteridae would have seemed very similar to ancient penguins,” said Dr. Paul Scofield, curator of natural history at the Canterbury Museum.
“These birds evolved in different hemispheres, millions of years apart, but it would be difficult to tell them apart from a distance.”
“The plotopterids looked like penguins, they swam like penguins, they probably ate like penguins, but they weren’t penguins.”
The parallels in the evolution of these groups of birds suggest an explanation of why the birds developed the ability to swim with their wings.
“Wing-powered diving is quite rare among birds; most swimming birds use their feet, “said Dr. Mayr.
“We believe that both penguins and plotodopterids 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.”
An article on the findings is published in the Journal of Zoological Systematics and Evolutionary Research.
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Gerald Mayr et al. Comparative Osteology of Penguin-like Middle Cenozoic Plotopteridae and Early True Fossil Penguins, with commentary on the origins of wing-powered diving. Journal of Zoological Systematics and Evolutionary Research, published online June 29, 2020; doi: 10.1111 / jzs.12400
