Dwarf Yellow Eyed Penguins

On Tuesday, we met the recently extinct crested penguin Eudyptes warhami, discovered by a team studying subfossil penguin bones from the Chatham Islands. The study also turned up a “bonus” penguin. Some smaller bones collected at the sand dune sites were originally thought to belong to one of the smaller modern crested penguin species. However, mtDNA revealed something unexpected. The bones turned out to belong to a dwarf population of yellow-eyed penguin!

Fossil bones of Megadyptes antipodes richdalei. Photos by Jean-Claude Stahl (Te Papa).

Yellow-eyed penguins are beautiful birds. They sport a yellow face mask, and as promised by their name have a bright yellow iris. It is easy to tell a yellow-eyed penguin skull from that of a crested penguin, due to the much more slender beak of the former. Yet, the rest of their bones are very similar and it is almost impossible to differentiate a large crested penguin from a yellow-eyed penguin based on the bones of the neck, flipper, or legs. Thus it is no wonder why the Chatham Island specimens were not identified immediately: the subfossil bones were so much smaller than the modern yellow-eyed penguins that the match seemed implausible.

A Yellow-Eyed Penguin, coming ashore in Dunedin, New Zealand. Photo by Daniel Ksepka.

Eudyptes warhami showed major DNA differences with living species, indicating it was a distinct species. Our team was also able to obtain intact mtDNA from the smaller bones. In this case they showed a very close relationship to modern yellow-eyed penguins. Indeed there were far fewer differences between the mtDNA sequences of the fossil and modern yellow-eyed penguins than between the fossil and modern crested penguins. Therefore, our team considered the smaller fossils to belong to a subspecies of the living Megadyptes antipodes, which we classified as Megadyptes antipodes richdalei, in honor of the late Dr. Lance Richdale, an expert on modern yellow-eyed penguins. While the concept of a subspecies is fairly messy, this recognizes that the Chatham Island dwarf penguins would have been easy to tell apart from their mainland relatives, but had not yet fully diverged genetically. Given a few hundred thousand more years, it seems likely that Megadyptes antipodes richdalei would have continued to evolve in isolation from its mainland relatives and eventually become a fully separate species.

 

Together, the crested penguin and yellow-eyed penguins of the Chatham Islands tell a complex tale of how species can be wiped out. Eudyptes warhami persisted for two million years only to be snuffed out in the blink of an eye. Megadyptes antipodes richdalei reveals a different kind of tragedy — it seems to have started on its way to becoming a distinct species, but had its evolutionary journey cut short before it had the chance.

Ancient DNA Reveals Lost Penguin Species

Today, another species joins the March of the Fossil Penguins. We welcome Eudyptes warhami, an extinct crested penguin discovered on the Chatham Islands, an island archipelago about 500 miles east of mainland New Zealand.

Paleontologists have uncovered the remains of over 50 species of extinct penguins, most of them millions of years old. Eudyptes warhami is unique – it died out only a few hundred years ago, making it the youngest fossil penguin. Whereas most of the penguin species that have ever lived went extinct long before humans evolved, this species actually lived side by side with humans for a short time. Unfortunately, that brief encounter turned out to be deadly.

Composite fossil skull of Eudyptes warhami, an extinct penguin species from the Chatham Islands. Photo by Jean-Claude Stahl (Te Papa)

An international team of researchers extracted mitochondrial DNA from subfossil bones discovered in sand dunes on the Chatham Islands. I was fortunate to be a member of this team, which was led by Tess Cole, a PhD candidate at the University of Otago in New Zealand. Our study was published today in the journal Molecular Biology and Evolution. This project combined skeletal morphology with DNA evidence to understand how the new penguin evolved. Skeletal features provided the first clue – the existence of a lost species was hinted at by earlier comparisons of penguin bones collected from sand dunes on the Chatham Islands. Alan Tennyson (a co-author on the study) and Phillip Millener examined penguin bones from these islands, and found that they did not match up with those of any living species. DNA evidence has now confirmed those suspicions. Our team extracted mtDNA (a type of DNA that resides inside the mitochondria of cells and is inherited from the maternal line). We counted the number of nucleotide substitutions, a measure of how many mutations occurred since two species shared a common ancestor. The large number of substitutions between Eudyptes warhami and its closest living relative, Eudyptes sclateri (a living species known as the Erect-crested Penguin) confirmed that the subfossil bones belonged to a genetically distinct species. Our team named the new species Eudyptes warhami, in honor of Dr. John Warham, who carried out pioneering studies on crested penguins in New Zealand.

Comparisons of the bones to those of modern penguins, along with DNA evidence placing the penguin firmly within the crested penguin part of the evolutionary tree, allow us to get a clear picture of what it would have looked like. The beak was very deep like modern crested penguins, suggesting the new species was adapted to pursuing small prey including krill. Modern crested penguins have decorative yellow head plumes, and the evolutionary tree suggests Eudyptes warhami would have been no exception. Together with measurements, these details allowed Bruce Museum artist Sean Murtha to create a beautiful life reconstruction of the new species.

Life reconstruction of Eudyptes warhami. Illustration by Sean Murtha.

Aside from the pristine bone preservation and intact DNA, another nice thing about new fossils is that they are young enough for carbon isotope dating. Carbon dating provides direct age estimates for organic material, but because of the relatively short half life of the radioactive isotope carbon 14, it cannot be applied to specimens that are more than 1 million years old. Carbon dates from the penguin fossils and associated remains of other birds suggest many of the specimens were only a few thousand years old. Indeed, some of the bones were found in piles of debris left behind at human cooking sites. This provides direct evidence that the Moriori, the first people to reach the Chathams, hunted Eudyptes warhami. The penguins appear to have been wiped out shortly after the Moriori arrived in the thirteenth century. How soon is a question that still remains unresolved, and will be revisited in future posts.

Though now lost, perhaps Eudyptes warhami can serve as a warning of the need for conservation efforts. For a long time, we thought penguins escaped the wave of human-driven extinctions that wiped out birds like the dodo, which disappeared in the seventeenth century, and the Great Auk, which became extinct in the mid-nineteenth century. Finding evidence that a crested penguin perished in the human era should remind us that we need to be even more careful with the species remaining under our stewardship.

Reference:

Cole T. L. D. T. Ksepka, K.J. Mitchell, A.J.D. Tennyson, D.B. Thomas, H. Pan, G. Zhang, N.J. Rawlence, J.R. Wood, P. Bove, J.L. Bouzat, A. Cooper, S. Fiddaman, T. Hart, G. Miller, P.G. Ryan, L.D. Shepherd, J.M. Wilmshurst, J.M. Waters. 2019. Mitogenomes uncover extinct penguin taxa and reveal island formation as a key driver of speciation. Molecular Biology and Evolution.