Clues to the evolution of modern penguins

Penguin fossils from around 62 million years ago in the Palaeocene suggest the ones we know today may have evolved earlier than previously thought.

The bones and skeletal remnants are among the oldest known penguin fossils. They were discovered between 2006 and 2011 in the Chatham Island archipelago east of New Zealand’s South Island, encased in the fossil-rich Takatika Grit rock formation.

At the time there was no ice cap at the South Pole and the seas around New Zealand were tropical or subtropical.

An international team analysed the fossils using virtual and physical methods to glean molecular and morphological data, identifying an ancient penguin new to science which they describe in the journal Palaeontologia Electronica.

Kupoupou stilwelli appears to be the oldest penguin known with proportions close to its modern relatives. It was large by today’s standards – around the same size as a king penguin – but would have been dwarfed by others existing at the time.

“Next to its colossal human-sized cousins, including the recently described monster penguin Crossvallia waiparensis, Kupoupou was comparatively small,” says Jacob Blokland, from Australia’s Flinders University.

Intriguingly, K. stilwelli could bridge a missing link between modern penguins and their ancestors.

The hindfoot bones (tarsometatarsi) are similar in shape to those of extinct giant penguins but shorter, much like in contemporary birds, Blokland says.

Although a couple of fossil penguin species from around the same period are similar in size, the foot bone suggests K. stilwelli used its feet differently to its ancient relatives, waddling on the land like modern penguins while also swimming through water.

The find adds to fossil analyses from overlapping periods in recent years that reveal a “remarkable and wide diversity of penguins”, says Blokland. This includes at least five species from the Waipara Greensand in Canterbury, New Zealand, and another species of comparable age from the Moeraki Formation in Otago.

As for the penguin’s new genus, “Kupoupou” means diving bird in Te Re Moriori, the language of the indigenous people (Rēkohu) from the Chatman Islands, and the species was named in honour of Jeffrey Stilwell from Monash University, Australia, who led the fossil expedition.

Another new species was indicated by larger, more robust bones, but can’t yet be confirmed due to lack of skeletal material.

The K. stilwelli discovery suggest penguins split from their common ancestor, the lineage leading to tubenoses (birds such as albatrosses, shearwaters and petrels), before non-avian dinosaurs went extinct in the Late Cretaceous.

The birds are likely to have “rapidly radiated to fill the ecological vacuum in the oceans left by the extinction of many marine animals”, says Blokland.

“It’s not impossible that penguins lost the ability to fly and gained the ability to swim after the extinction event of 66 million years ago, implying the birds underwent huge changes in a very short time,” adds senior author Paul Scofield from New Zealand’s University of Canterbury – one of the researchers who described Crossvallia waiparensis.

“If we ever find a penguin fossil from the Cretaceous period, we’ll know for sure.”