Posts Tagged ‘Brains’
Digimorph is a digital library of Computer Tomography (CT) datasets. It is a wonderful tool for researchers and for people who just love morphology. Last week the fossil Paraptenodytes antarcticus scan was uploaded to the site. You can see it here. Digimorph lets users test drive a variety of imaging tools, so you can scroll through individual slices of the fossil skull, spin it around in three directions, and take a peek at different views of the virtual brain model. Digimorph is packed with other great content too, including a variety of living penguin skull scans, dinosaur fossils, whole pickled animal scans and more.
Paleontologists today are lucky. We have new tools that could only be dreamed of a few decades ago. One of these is rapid prototyping, which allows us to create replicas of important fossils – or even models of structures that did not actually fossilize! In the case of the Paraptenodytes brain project, we were able to create an accurate physical model of the brain that can be studied, displayed, and shared with other scientists. This is a great opportunity, because all we originally had was the skull. Now, we have an endocast of the brain too, thanks to CT reconstruction. It is almost like creating a new “bonus” fossil.
How can this be done? Rapid prototyping is basically 3D printing. After loading up a digital file of the object to be printed, the prototyping machine builds the physical model layer by layer, using a nylon composite powder. A laser is used to sinter the powder together. This means that the laser causes the atoms in the powder to diffuse across the boundaries of the particles, joining the layer together into a single piece without actually melting it. A the end, we have an amazing model of a penguin brain.
One of the great things about prototyping is that the files are digital, so they can be shared easily across long distances. I could transfer a copy of the Paraptenodytes brain files to a colleague in another country in a few minutes time and they could print one out in their lab. Another advantage of this technology is that unlimited copies can be made with no degradation – unlike the case of traditional molds, which slowly become less accurate with use due to wear and tear. Finally, the prototypes can be made out of other materials besides nylon composites – stainless steel, ceramics, colored plastics and even silver are possible. One day if I become a millionaire, I may treat myself to a solid gold Paraptenodytes brain.
The Abstract is a blog that covers new research at North Carolina State University. They cover really interesting stuff, like the physics of the Olympics and of course fossil discoveries by NC State paleontologists. Today Tracey Peake wrote a nice article about our team’s brain research. Check it out here:
It’s hard to quantify intelligence in a bird. They won’t sit still for an IQ test and may not have learned geometry in their early years anyway. While some birds such as parrots can actually develop a vocabulary of human words, penguins stick mostly to rather harsh braying sounds. Although we can’t give them a grade, we do know that penguins have many complex behaviors, including bonding rituals shared with mates, coordinating “rafts” of multiple birds to come ashore smoothly, and even a penchant for stealing from other penguins. These observations suggest penguins are smart animals overall.
What about fossil penguins? Paleontologists have one neat tool to estimate intelligence – Encephalization Quotient (EQ). EQ is a measure of the brain size of an animal relative to its body size. EQ controls for allometry – that is, it corrects for the fact that larger animals have smaller brains relative to absolute size. An elephant’s brain accounts for only about 0.2% of its total mass, while a cat’s accounts for a whole 1%. However, when you control for size scaling, both have an EQ of around 1, which is the baseline for mammals. Biologists calculate whether an animal is above average or below average by plotting out brain mass versus body mass for a large group of species and then checking whether a particular species falls above the line or below the line. EQ levels roughly correlate to intelligence, with the highest levels seen in chimpanzees (2.5) dolphins (4) humans (7.5).
Because only the size of the brain and an estimate of mass is needed, it is possible to calculate for extinct species by either physical means or virtual means. Filling the braincase with millet grains to estimate volume was one early technique. Today paleontologists often use CT data for determining brain volume.
We plotted the brain size and body mass of a variety of bird species in our study, and found that Paraptenodytes falls a little bit above the line, suggesting it was a quick-witted penguin. There is something else to consider about the plots though. Penguins are much denser than other birds because of their solid bones and the thick fat layers they build up for insulation. So, a penguin that is roughly the same size as a bird like a seagull will weight more. We used mass as the measurement to make the plots, but if we used another measurement like body length or standing height, the penguins would move up higher above the curve, Does that mean penguins really have a higher encephalization quotient? It’s hard to say. Perhaps they just require more cerebral volume to control their heavier bodies. Alternatively, penguins may need enlarged brains to survive in the very complex world they inhabit. Spending part of their time hunting at sea and part of their time moving about on land to build nests, raise chicks and socialize with other birds in their colonies involves a lot of different, complex behaviors. It may take a high-power brain just to keep all up with all these activities.
Bird brains are wonderful structures. Indeed, “bird-brained” is an unusually poor insult, because the avian brain is one of the most complex seen in vertebrates. “Turtle-brained” might be a better insult in terms of neuroanatomy. That slight would be more hard-hitting if you meant to slander someone’s higher reasoning abilities. While bird brains are larger relative to body size than those of turtles, crocodiles, lizards and even some mammals, size is not the only thing that matters. Different parts of the brain are responsible for different functions. Deciphering the proportions of different parts of the brains of extinct animals can therefor give us insight into their biology.
Vertebrate brains can be divided into three major sections: the cerebrum, cerebellum and medulla oblongata. In our Paraptenodytes study, we were able to identify all three from the scans of the nicely preserved fossil. The cerebrum is where most of the “higher” functions of the brain like memory, communication and reasoning are conducted. This part of the brain is split in two hemispheres in birds, just like in humans. At the very front of the cerebrum, the olfactory bulbs connect to the brain. These structures are involved in the sense of smell, and in penguins are quite small. That makes sense, because penguins mostly locate their food using sight, not smell. In birds like albatrosses and turkey vultures that locate food via scent, the olfactory bulbs are much larger. Next up is the cerebellum. Some of the important functions of this part of the brain are controlling movement and balance. One of the projections of the cerebellum is the flocullar lobe, which is associated with stabilizing vision during rapid movements of the head. This structure tends to be enlarged in diving birds, possibly in relation to the twisting and turning underwater acrobatics that are invoked to catch prey. Paraptenodytes is no exception to this pattern, and has a strongly developed floccular lobe. In front of the cerebellum lie the optic lobes, which as you might expect are associated with visual acuity. These are well developed in most birds, with some real impressive size in owls and a great reduction in nocturnal birds like kiwi. Below the optic lobes there is a space for the pituitary gland which also shows up in endocasts. This gland secrete hormones that control growth rates and other metabolic functions. At the rear, lower portion of the brain is the medulla oblongata. This region is associated with many of the important life functions we take for granted, like regulating heart rate and breathing. This region is also where many of the cranial nerves leave the brain and branch out to the parts of the body they innervate. Most of these nerves can be identified in the endocast, because they form small openings called foramina in the places where they leave the protective bony braincase.
So, at the end of the day we can learn much more about the brain than just its raw size. One important caveat to all of this is that there is even more subdivision of duties in the brain. Different layers of brain cells are associated with different tasks as well – navigation, memory, vocalization and problem solving parts of the brain are all layered inside the cerebrum of a living bird, but we will only ever be able to decipher the total cerebrum size from an endocast, not the depth of each layer. While this is a real limitation, the data that paleontologists are gaining from even the volumes of major structures is greatly expanding the limits of our knowledge about extinct animals.
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.