March of the Fossil Penguins

Inguza is fast becoming one of my favorite fossil penguins.  Last December, I spent several weeks in South Africa studying fossil penguin bones in museums and at field sites with my friend and colleague Daniel Thomas.  Much of our time was spent examining, measuring, and analyzing bones of a somewhat runty penguin named Inguza predemersus.  This species was on the small end of the scale, and would have stood about chin-high next to the living Blackfooted Penguin (a species that is also known as the Jackass Penguin or the African Penguin).  Bones of Inguza are very common in the Langebaanweg Quarry, a famous fossil site that has produced some of the most amazing fossils in Africa, including the remains of a miraculous short-necked giraffe and Africa’s first fossil bear (completely unexpected as no bears live on the continent today).  Daniel Thomas and I were able to learn a lot about the evolutionary history of African penguins by studying Inguza, and I’ll post more about that soon.

A skeletal reconstruction of Inguza predemersus with extant Blackfooted Penguin (Spheniscus demersus) for scale, from Ksepka and Thomas (2011). Blackfooted penguin art by Barbara Harmon, Inguza art by Kristin Lamm

Holding the bones of Inguza side by side with bones from modern Blackfooted Penguins, I often wondered whether the two had ever met.  Among the hundreds of penguin bones from the Langebaanweg quarry, there is no trace of Blackfooted Penguin remains.  The youngest Inguza fossils are about 5.1 million years old, and the oldest Blackfooted Penguin bones are between 250,000 and 400,000 years old.  There’s a pretty large gap in the African fossil record between these points though, where few marine birds of any sort are known.  It’s possible that at some time within that interval, the last Inguza individuals noticed a new neighbor in their colonies as the founding Blackfooted Penguin population arrived.  Perhaps they lived side by side, choosing different prey. Perhaps they jostled uneasily for nesting sites.  Perhaps the new arrivals even contributed to the extinction of Inguza by outcompeting that species.

Or, its possible the last Inguza died out before any Blackfooted Penguins set foot in Africa.  In the most extreme scenario, there may have been NO penguins at all in Africa at some point 1-4 million years ago.  Blackfooted Penguins could have arrived into a “penguin vacuum” and set up shop wherever they pleased.  Not knowing what happened is one of the reasons we keep going back to the field to collect more fossils.  As we fill in the blank parts of the record, we will come closer to understanding what actually happened on those beaches millions of years ago.

Reference:

Island birds have undergone some of the most fascinating radiations in evolutionary history, producing such wonders as the “toothed” Moa-Nalo ducks (Chelychelynechen, Thambetochen and Ptaiochen) of Hawaii and the enormous nine foot tall Elephant Birds (Aepyornis) of Madagascar. Island birds have also been devastated by human exploitation. The Dodo (Raphus), once an inhabitant of Mauritius, is an icon of extinction. Sadly, the Dodo is only the most well-known member of this club. Giant moa were hunted to extinction in New Zealand. Dozens of unique birds including Moa-Nalos, flightless ibises and nectar-feeding songbirds were wiped off the Hawaiian Islands following the arrival of humans. Today, many of the native bird species of Guam are severely endangered by predation by invasive snakes, introduced by humans.

Penguins were long thought to have been exempt from this fate. Because they can retreat to the sea where they are difficult to capture, penguins are somewhat less vulnerable to hunting than many other types of birds, particularly other flightless ones. Although historically harassed by humans in many ways, no penguin species was thought to have been wiped out until a very recent discovery. A team of researchers in New Zealand and Australia rounded up subfossil bones from archeological sites from the South Island of New Zealand ranging from 200 to 1500 years in age. They extracted ancient DNA from the bones and compared the sequences to other collected from live Yellow-Eyed Penguins (and museum specimens of the same species). The findings were startling – a wide genetic distance was uncovered separating the pre-1500s mainland penguin bones from post-1500s bones. The younger bones belong to the modern Yellow-Eyed Penguin (Megadyptes antipodes), and their DNA sequences cluster with samples from living individuals and subfossil bones of the species from outside the mainland. However, DNA from the pre-1500s subfossil bones from the mainland don’t cluster with the Yellow-eyed Penguin samples. DNA evidence suggests a distinct species of penguin was living on the South Island of New Zealand. This conclusion is backed up by careful comparisons of the bones, which demonstrates size and shape differences outside the range of normal variation seen in living Yellow-Eyed Penguins. The newly recognized, recently extinct species was named Megadyptes waitaha by the team.

Bones of the living Yellow-Eyed Penguin Megadyptes antipodes (left side of each pair) and the recently extinct Megadyptes waitaha (right side of each pair).

Dating of the fossil deposits suggests that Megadyptes waitaha survived all the way up to the time of colonization, overlapping with the fist human settlers to arrive from Polynesia. Direct evidence from associated artifacts shows that humans actively hunted these penguins, and the circumstantial evidence from timing strongly points to overexploitation as the proximal cause of their extinction. A second interesting finding of this study is that the modern Yellow-eyed Penguin seems to have benefited from the extinction of Megadyptes waitaha. Comparisons of the morphology of subfossil penguin bones, along with DNA extraction, reveals that in the 1500s the Yellow-eyed Penguin was restricted to sub-Antarctic islands such as the Auklands. During this same time period, Megadyptes waitaha inhabited a wide swath of the east coast of the South Island. Flash forward to 1800, and Megadyptes waitaha is nowhere to be found anywhere. Yellow-eyed Penguins crop up nearly everywhere that Megadyptes waitaha used to be. The timing suggests that as hunting patterns shifted, prime penguin real estate vacated by Megadyptes waitaha was reclaimed by Megadyptes antipodes.

So, Megadyptes waitaha is now a ghost on our collective consciences. These bones are something to think of when penguin populations suffer from oil spills, rampaging stray dogs, or overdeveloped beaches. There were at least 20 species of penguins when humans first appeared, and now we have 19 species left to enjoy and protect.

References:

Boessenkool, S.; Austin, J.J.; Worthy, T.H.W.; Scofield R.P.; Cooper, A.; Seddon, P.J.; Waters, J.M. 2009. Relict or colonizer? Extinction and range expansion of Penguins in southern New Zealand. Proceedings of the Royal Society of London B 276:815-821.

James, H.F. and Olson, S.L. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part 2. Passeriformes. Ornithological Monographs, 46: 1-88.

Olson, S.L. and James, H.F. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part 1. Non-Passeriformes. Ornithological Monographs, 45: 1-88.