Archive for March 2013
My colleague Dr. Daniel Thomas has posted some behind the scenes information about the South African penguin fossils we recently reported, including a great explanation of how geochemistry can help us determine under what conditions fossils were deposited and altered, and sometimes place them in time and space.
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.
Some new penguin bones have been discovered on the frozen continent of Antarctica. It may seem natural to think that most fossil penguins would come from Antarctica, given our fascination with the icy travels of species like the Emperor Penguin. However, there are few places paleontologists can look for fossils on the continent. Very few rocks are exposed for prospecting due to the overlying ice sheets. Up until now, all of the penguin fossils have come from West Antarctica. In fact, they have all been from Seymour Island, which is part of the archipelago of islands off the tip of the Antarctic Peninsula. Although these fossils include some amazing species, this geographical restriction has greatly limited our knowledge of the history of the southernmost penguins. The oldest reported bones are assigned to the species Crossvallia unienwillia from the late Paleocene (about 55 million years ago). We know there was a diverse group of species of all sizes, including some giants, thriving from about 50 million years ago to about 35 million years ago. Most of this interval in Earth history was quite warm, and the penguins were living in a fairly temperate environment complete with forests. Over the next 35 million years, climate cooled leading to the growth of ice sheets which eventually covered almost all of Antarctica.
What happened to the penguins? Did they adapt? Did they die out? If so, when did new species replace them? Today, several species of penguin breed in Antarctica including the Emperor Penguin, Adélie Penguin, Chinstrap Penguin, Gentoo Penguin, and Macaroni Penguin. We know that these modern species are distantly related to the original archaic penguin inhabitants of Antarctica. But, because of the big gap in the fossil record we are not sure when the new species first arrived and what happened in the meantime.
The new fossils were discovered at Prince Charles Mountains, which is in East Antarctica, almost directly opposite from the Seymour Island sites. Two flipper bones, a humerus and a radius, were found in a shell bank. This was a fortuitous place for the find, because shells can be dated with isotope methods. The scientists looked at the levels of a radioactive isotope of the element Strontium to figure out the age of a scallop found near the penguin bones. These tests indicate the fossils are 10.2 million years old, much younger than the previous fossil records from Seymour Island.
Features of the bones suggest they belong to the genus Spheniscus, the group of “tuxedo penguins”. That’s an interesting fact, because today Spheniscus penguins (including Galapagos and Black-footed Penguins) are some of the species most adapted to warm conditions. They make it south as far as Tierra del Fuego, but don’t cross over to Antarctica. Because things are already quite chilly in the south by 10 million years ago, it is a surprise to see a Spheniscus penguin in the region. I am very excited by the first announcement of bones, and hope more is in store. East Antarctica may well hold some important secrets of penguin evolution.
Jadwiszczak P., Krajewski K.P., Pushina Z., Tatur A. Zieliński G. 2012. The first record of fossil penguins from East Antarctica. Antarctic Science, FirstView Article, pp 1-12, DOI: http://dx.doi.org/10.1017/S0954102012000909; Published online: 15 November 2012.