Posts Tagged ‘Extinction’
As we discussed last post, penguins were very diverse in Africa in the past. We have two good geological time slices, one from the Miocene and one from the Pliocene. At both times, there were four different species inhabiting the southern coast. Today, there is only one. This raises the question: what happened to all those extinct species? It might seem natural to point the finger at humans, since we have been involved in the extinction of many flightless birds such as the Dodo, Moa, and Great Auk. In this case, the fossil record seems to exonerate us. By the time the first human settlers arrive in South Africa, all of the extinct species had already vanished and only the modern Black-footed Penguin was hanging around. Archeological sites show no evidence of early humans roasting up big piles of penguins at campsites, suggesting that overhunting had no role in the extinctions.
A more plausible explanation involves sea level change. Penguins love islands. This is because the land is actually a dangerous place for penguins. Predators like stoats, cats, dogs and even large birds pose a big danger, especially to hatchlings and eggs. This is one of the reasons why penguins tend to breed in isolated places, where there are likely to be few land mammals to harass them. Today, it is possible to see Black-footed Penguins nesting in places like Boulders Beach on the coast near Cape Town. However, the majority of the regional population nest on small offshore islands, where they are safer from land predators.
Over the past 12 million years, sea level along the African coast has ramped up and plunged down like a slow-motion roller coaster. During the time the fossil species lived, there were far more islands in the area. This is because higher sea levels swamped the coast, submerging many low-lying areas and turning hilltops into islands. These areas would have been prime penguin real estate. As sea level dropped towards the present, the islands would have been reconnected to the mainland, allowing terrestrial predators to invade. We suspect this could have removed much of the suitable nesting colony areas, resulting in a lower carrying capacity for penguins and the extinction of some species.
Roberts, D. L. et al. 2011 Regional and global context of the Late Cenozoic Langebaanweg (LBW) palaeontological site: west coast of South Africa. Earth Sci. Rev. 106, 191 – 214.
Evidence is mounting that Africa was once quite the penguin hotspot. Last year, Dr. Daniel Thomas and I published a paper looking at the biogeography of African penguins – that is, deciphering where they came from. We found evidence that penguins likely made it all the way across the Atlantic Ocean several times, crossing from South America to Africa by riding out the currents of the South Atlantic Gyre. The fossil species we looked at in that study were about 5 million years old. Today, our second article was released, detailing fossils from older deposits. These fossils come from the Miocene Saldanha Steel locality, which dates to nearly 12 million years in age. Penguin bones from Saldanha Steel have a sort of rugged appeal. They are stained a dark orangy-brown color and have been tumbled around with rocks and sand till they are quite worn. This created a bit of a puzzle, requiring some careful comparisons (and a little bit of adhesive) to figure out what each bone represented.
Although only isolated bones have been found so far, it is clear that there were at least four different species in the area around 12 million years ago. We can tell this based on the size differences of the elements that were found. Biggest of the Saldanha Steel penguins is a hefty bird that was about the same size as the living King Penguin (the second largest living species) based on the length of its flipper bones. In fact, the sternum of the animal suggests it may have been a relative of King and Emperor Penguins, but we will need more fossils to be sure. There are two average sized penguins, represented by an assortment of leg and flipper bones and one lower jaw bone. Smallest of the Saldanha Steel penguins was a tiny Little Blue Penguin sized species that would have been only a foot tall in life. We are lucky to have detected the presence of this tiny fellow, because small bird bones are rare at the site. Only a single vertebra (part of the spinal column) was uncovered. Despite being just a small bit of bone, it is an clear match for a penguin. Penguins have special ball and socket style joints in their lower vertebrae that almost no other birds possess. Beyond this, they have lost the pneumatic openings exhibited by the other birds which have this style of vertebrae (cormorants and gannets).
We were surprised to find so many different size classes living in the area. In the next post, we will explore what may have been going on back in the Miocene.
Reference: Thomas, D.B. and D.T. Ksepka. In Press. A history of shifting fortunes for African penguins. Zoological Journal of the Linnean Society.
Macquarie Island is an isolated island of the South Pacific, located roughly half-way between Australia and New Zealand and quite far to the south of both. The island is home to King Penguins, and recently a team of biologists published a study of ancient and modern penguin DNA from bones collected on the island, some of them up to 8,000 years old, to reconstruct patterns in genetic diversity in the early and modern history of this island.
These samples reveal patterns in genetic diversity of King Penguins over a period of great stress. Two King Penguin colonies were originally present on Macquarie Island. Sadly, human settlers wiped out all of the penguins in the colony at the Isthmus (the northmost part of the island) by 1894 and reduced the population at Lusitania Bay to about 3400 birds – a tiny fraction of the original population.
Sounds like the final days before a tragic loss of the entire islands penguin fauna. However, just in time, Macquarie Island was made a wildlife refuge in 1930. Over the next 80 years the penguins rebounded and some birds from the Lusitania Bay colony moved north along the coast and re-started the Isthmus colony. One of the interesting things that the DNA study revealed is that the penguin have reached levels of genetic diversity close to those that existed before human arrival. Genetic diversity is important. A plunge in the number of genotypes can leave populations vulnerable to genetic disorders carried on recessive genes. Higher genetic diversity also provides resilience to changing environments. While many ancient DNA studies have revealed that population crashes can result in genetic bottlenecks, the Macquarie Island penguins seem to have rebounded – possibly through fortuitous survival of genetically diverse individuals and perhaps also through arrival of a few King Penguins from other areas of the southern oceans.
Thanks to protections put in place, there are almost half a million King Penguins living on Macquarie Island today. A hopeful conclusion of this study is that even after being severely pressured, penguins can rebound if we just allow them the chance
Heupink, T.H., J. van den Hoff, and D.M. Lambert. In press. King penguin population on Macquarie Island recovers ancient DNA diversity after heavy exploitation in historic times. Biology Letters.
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.
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.
Ksepka, D.T. and D.B. Thomas. In press 2011. Multiple Cenozoic invasions of Africa by penguins (Aves, Sphenisciformes). Proceedings of the Royal Society B Biological Sciences.
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.
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.
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.