Archive for July 2012
Today, our team’s latest research project was published online in the Zoological Journal of the Linnaean Society. Along with collaborators Amy Balanoff, Stig Walsh, Ariel Revan and Amy Ho, I got the chance to take a peek at the brain of the fossil penguin species Paraptenodytes antarticus. Over the next few posts, I’ll share what we found.
So how can we look at a fossil penguin brain? After all, brain tissue doesn’t fossilize like bone. In fact, it is about as gushy a part of a penguin as any. A penguin brain left out on the table will degrade into featureless sludge in just a few days, let alone a few million years. The answer is studying a cast of the brain – a copy of what it looked like in life.
For many years, the only two ways paleontologists could get a good picture of the brain of an extinct species were by finding natural endocasts or by using latex molds. Natural endocasts form when the brain cavity of a skull gets filled in with a substance like mud or silt after the brain decays away, leaving empty space. As these sediments harden, they create a replica of the brain. That’s great for the lucky paleontologist who finds one, but such natural endocasts are rare. Sometimes, the rest of the skull gets destroyed while the rocky endocast remains. Finding one of these is a bit of a mixed bag – an endocast is really informative, but if you don’t know what species it belongs to, it is hard to interpret.
Latex molding is another way to get an endocast. Paleontologists can create artificial endocasts by injecting liquid latex into an empty skull and letting it dry, then using the latex as a mold to create a plaster endocast. This method is useful, but sometimes it is impossible to apply because the skull is filled with rock and is too delicate to clean out the brain space without damaging it.
Luckily, there is a third option. Today, many paleontologists study the brain morphology of extinct animals using x-Ray Computer Tomography Scans (CT scans). CT technology is a powerful tool for paleontologists, because it lets us study endocasts from many specimens we otherwise wouldn’t have access to. Scanners are widely used by doctors and veterinarians to diagnose medical problems. For example, a doctor at a hospital might send a person through to check for internal injuries after a car crash, and a vet may send your dog through to find out where the golf ball he swallowed has gotten to! For our study, we brought the fossil Paraptenodytes antarcticus skull to a hospital. Not your standard patient – we had to enter the age as 22 million years!
The actual scan is composed of a series of 2D x-ray slices. In this case, we had several hundred individual slice images and had to work together to isolate the brain in each one (painstaking work!). Once all the slices were studied, we were able to stack them up and make a 3D model of the brain. Later this week, we can tour the model and see exactly what was on the mind of this ancient penguin.
Ksepka, D.T. A.M. Balanoff, S. Walsh, A. Revan and A. Ho. In Press. Evolution of the brain and sensory organs in Sphenisciformes: new data from the stem penguin Paraptenodytes antarcticus. Zoological Journal of the Linnean Society.
Last month I spoke to the folks at A Moment of Science about fossil penguins. Here is one of their recent stories about how penguin preserve heat at their feet.
No fossil penguin news this week, though I am awaiting the launch of a new paper by our team to share at March of the Fossil Penguins. Instead, let’s take a penguin humor break. This video of a Little Blue Penguin (Eudyptula minor) being tickled has already been viewed 5 million times, so why not share it with a few more people?
Mandible is the scientific term for the lower jaw. Whereas we humans have a lower jaw made of only a single bone (the dentary), penguins have a more complicated mandible made up of half a dozen different elements (the dentary, splenial, articular, prearticular, angular and surangular). These bones are all connected in penguins, though some of the joints are rather loose, which allows the jaws to flex a bit This process is called kinesis. At the front tip of the mandible, the left and right sides of the jaw meet and connect at the symphysis. This region is often a very firm connection, with no movement possible. One of the many unique things about living penguins is that they have a very short, flexible connection at the symphysis. This allows for more “play” in the jaws, which may be helpful when a bird has a mouthful of thrashing prey. Not all penguins have a short symphysis though. The spear-beaked fossil species Icadyptes salasi, for example, has a long, firm connection which is probably related to a different style of prey capture (e.g., spearing versus biting).
Different types of penguins exhibit different mandible shapes. The depth of the mandible can be an important clue to the type of food penguins eat. Many fish and squid specialists have low, slender mandibles like most other birds. Krill-loving species like the Adélie Penguin often show much deeper jaws. This difference is interpreted as an accommodation for the larger, spikier tongue of those penguins, which helps them capture shoaling prey. For this reason, I am always eager to measure the jaw dimensions of fossil penguin specimens that I stumble upon in the field (or in museum drawers). Its quite interesting to note that so far, none of the ancient penguin species that have been discovered had deep jaws. This suggests they had not yet adapted specializations to catching krill. Perhaps this feeding strategy was acquired only recently in penguin evolution, as Antarctic ice sheets spread and gave rise to new ecosystems.