Archive for September 2011
Penguin bones are common in the fossil record. Trillions of penguins have lived over course of the Cenozoic, and a tiny portion of these died in environments favorable to fossil preservation. Some fossil penguins are giant and others tiny, some are complete skeletons and others single bones, some pristine and others badly damaged by erosion or chewed on by sharks. However, almost all of them are bones of adult birds. This is actually not too surprising when you think about penguin life cycles. Adults spend most of their time in the water, so it is easier for animals that die and sink to the bottom to be covered by sediments and have a chance at fossilization. Hatchling and juvenile penguins stay on land though, and if they don’t make it to adulthood it often means they were gobbled up by a predator and leave no trace in the fossil record.
Hatchling penguin fossils can be really informative, because they provide unequivacal evidence that a breeding colony existed in the area. Usually, this is very hard to prove in the fossil record, because modern penguins are infamous drifters. Some travel more than a thousand miles over the course of a normal year before returning to their breeding grounds, and a few random individuals always end up on the wrong continent annually (like New Zealand’s stray Emperor Penguin). Because of these penguin proclivities, it is hard to be sure whether adult fossil penguin bones we find at some sites belong to penguins that bred there, or instead belong to a bird that was just passing through.
Unfledged birds are those that haven’t yet left the nest. In dramatic cases, fledging occurs when a baby bird is pushed out of the nest by its parent, and instinctively takes its first flight. For penguins, fledging involves a trip into the ocean instead. That’s why hatchling penguin bones can be so informative to paleontologists. If we find a fossil from an unfledged bird, we know with certainty that bird was hatched in the area because it was too young to have started swimming.
Part of the story in my recent paper with Dr. Daniel Thomas is based on tiny fossils from hatchling penguins. There are quite a few fossils of juvenile animals in the South African records from Langebaanweg. These bones show a very spongy texture because they have not completely ossified yet and parts remain cartilaginous (just like our own bones when we are children). There are also fossil parts of compound bones that remain separate in hatchlings but fuse together in adults. For example, the three small bones on the right side of the photo are parts of the foot that join completely together in fully grown penguins. In order to figure out how old these penguins were when they perished, we looked at modern skeletons of hatchling, juvenile and adult penguins in museums. Based on the patterns we observed, we aged the bones in the photo to a very young bird, which would not yet have started moulting into its adult feathers (and therefor wouldn’t be ready to take its first plunge). It’s sad to think these birds never had a chance to enter the marine realm, but studying their fossil remains pins down the location of their species breeding ground pretty precisely. That’s a rare and valuable peek into a vanished ecosystem.
The Radio In Vivo interview is now posted. We cover a lot of ground, but there are some penguins in the last third.
A new paper in Journal of Paleontology by Mark Uhen, Nicholas Pyenson, Tom DeVries, Mario Urbina, and Paul Renne highlights some exciting Peruvian fossils, including the oldest whales from South America. I’ve had great times in the field in Peru with the first four authors, on a joint expedition hunting for penguins and whales. Two new whale species are among the finds, and they prove that whales were able to travel widely around the Southern Hemisphere even before becoming fully pelagic. Some amazing artwork accompanies the story, with a cameo by the Peruvian fossil penguin Icadyptes. Get more on the story by Nick Pyenson at the Smithsonian’s Ocean Portal Blog.
Tomorrow morning at 11am EST, I’ll be giving an interview about paleontology on Radio In Vivo, a Triangle Area Science program. Host Ernie Hood and I will talk about all types of fossils, and penguins are sure to come up. If you are in the Triangle area, feel free to tune in to WCOM-FM 103.5.
You can also listen to the archived interview anytime at:
Happy Feet, the Emperor Penguin who got lost and ended up in New Zealand, has been released back into the ocean. People the world over are hoping he will make his way back to his natural home in Antarctica. You can track his progress (monitored by a satellite transmitor attached to his tail) at: www.nzemperor.com
In our recent paper in Proceedings of the Royal Society B: Biological Science, Dr. Daniel Thomas and I attempted to unravel the biogeography of the extinct penguin species of Africa – that is, to figure out where they came from.
There are two main hypotheses for the history of Africa’s penguin fauna. One is that they represent an endemic radiation. In this scenario, a single founding population of penguins (perhaps just a few individuals) arrive in Africa to find it a wide open swath of penguin paradise. With plenty of prey available in the cold waters of the Bengali current and ample safe rocky islands to nest on, these colonizing individuals could have rapidly multiplied. Over time, the original species could have split off into multiple species as selective pressures pushed for different traits. Endemic radiations are well-documented in birds, most famously in the case of Darwin’s Galapagos finches. In that instance, a single species of finch split into more than a dozen distinct species over the course of a few million years. Arriving in a near ecological vacuum, the founding finches evolved a range of different beak shapes and behaviors to exploit different food sources. It is not too hard to image the same thing happening as penguins arrived on a continent new to them, without any direct competitors.
The second hypothesis is that the extinct penguin species arrived separately, in multiple waves of dispersal. Each species would thus have a separate ancestor on some other continent. Waves of dispersal are also common in island avifaunas. An amazing example is Hawaii’s assemblage of bizarre ducks and geese, now tragically almost entirely extinct. One of the few surviving species is the Nēnē, a descendant of wayward Canada Geese that became stranded on the islands. In the fossil record we find some stranger examples, including the giant “toothed” Moa-Nalos. These thundering flightless birds weighted up to 15 pounds and evolved from Mallard Ducks that gave up flight in favor of large size. Another intriguing example is Talpanas, a litter-foraging duck that was probably nearly blind and nocturnal, guiding itself with its powerful sense of smell. This species evolved from a Ruddy Duck-like ancestor.
In order to test which hypothesis was more likely, we constructed an evolutionary tree of the South Africa penguins and fossil species from elsewhere. What we found is that two of the extinct species, Inguza predemersus and Nucleornis insolitus, were NOT close relatives of the living Blackfooted Penguin (the only species that breeds in Africa today). This rules them out as being either ancestors of the Blackfooted Penguin or part of an endemic radiation. In fact, Inguza predemersus and Nucleornis insolitus were not even particularly close relatives of one another, and so must have arrived in Africa separately rather than splitting off from a single ancestor. The waves of dispersal hypothesis wins out. At least three separate dispersals must have occurred. There may have been even more, because two other species of extinct penguins are known from Africa’s fossil record. Unfortunately, we know too little about them to guess where they belong on the evolutionary tree. If we later find out they are also related to other non-African penguins, we could have up to five dispersals on our hands.
So, how did all these waves of penguins make it to Africa? It seems like ocean currents played a big role. One major circulation system in the southern oceans is the South Atlantic Gyre. This system of currents creates a huge counterclockwise flow that may have served as a “penguin conveyor belt” from South America to South Africa. Penguins have been in South America for at least 40 million years, and this continent was identified as the most likely area of origin for the ancestors of the African penguins in our analysis. One possible scenario involves penguins from the South American coast getting caught up in the Brazil Current while foraging out at sea, and swept away from the coast. From here they could become entrained in the east-flowing South Atlantic Current and after a long journey (penguins can survive at sea for months at a time) the Benguela Current could have swept them back up the coast of Africa to dry land. We propose that this type of current-aided dispersal happened may times, and that currents are the main reason why Africa has penguins today, while Madagascar, which is surrounded by unfavorable currents pushing southward and away from the coast, does not.
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.