Penguins are known for the diminutive stature. Even the tallest of the species, the Emperor penguin, averages at around 4ft (1 metre), while the smallest – the aptly named little penguin – measures just 13in (33cm) in height.
So it came as some surprise when researchers from Germany and New Zealand happened across the fossilised remains of an extinct penguin, from approximately 55 million years ago, that would have towered over its modern counterparts.
The giant species, dubbed Kumimanu biceae, was identified from a partial skeleton dating back to the late Palaeocene of New Zealand. Its femur measured 161mm, from which the team estimated the penguin would have weighed 101kg and had a body length of 1.77m (around 5ft 8in), making it one of largest penguins reported to date. K. biceae is also one of the oldest known penguin species, as only two other species are known from 62 to 58 million years ago.
Gigantism is a known feature of penguin evolution, in which the size of ancient species exceeded that of the largest living penguins. Giant specimens are well documented from approximately 50 to 20 million years ago, but older examples are far more rare.
This is, in part, due to the lack of remains but also the difficulty in determining the size of extinct penguins from such fragmented bones. Different species may have different proportions, for example, so simply knowing the length of a thigh bone isn’t always enough to gone on in the same way it is with humans, as an example.
That said, the major limb bones are “distinctly larger” than most known Sphenisciformes – the official classification of penguins.
This image shows the partly prepared skeleton of the Paleocene giant penguin Kumimanu biceae. The rectangles emphasise the humerus and a bone from the shoulder girdle (coracoid)
“Even our conservative estimate of 185mm for the minimum total length of the humerus of K. biceae exceeds the humerus length of almost all other giant penguin species,” explained author Gerald Mayr from the Senckenberg Research Institute. “The maximum estimate of 228 mm, which is based on the humerus proportions of other Paleocene Sphenisciformes, is only surpassed by an estimate based on very large fossils from the late Eocene of Antarctica.”
The authors believe that the new species represents an “independent origin of giant size”, which took place soon after the origin of penguins and when the birds transitioned from flying to diving.
Previous studies have found that an increase in feeding competition among marine animals throughout the Paleogene played a significant role in the extinction of giant birds, including penguins and other large wing-propelled diving birds. Competition from pinnipeds (seals) for safe breeding areas has been quoted as a reason, too.
The humerus (top) and a bone from the shoulder girdle (coracoid, bottom) of the Paleocene giant penguin Kumimanu biceae, compared to the corresponding bones of one of the largest fossil penguins known to date (Pachydyptes ponderosusfrom the Eocene in New Zealand) and those of an Emperor Penguin
As the authors explain, the disappearance of giant penguins coincided with the rise of marine mammals, but the exact causes remain poorly understood.
“In any case, the evolution of penguins appears to have been strongly influenced by non-avian vertebrates: whereas the end-Cretaceous extinction of larger marine and terrestrial predators may have been the ecological driver for the loss of flight capabilities in the earliest Sphenisciformes” and may have ultimately led to the demise of the giant species towards the Miocene.
The research is published in the journal Nature Communications.
Images: G. Mayr/Senckenberg Research Institute
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