How Computed Tomography Reveals the Internal Anatomy of Bat Skulls
November 15, 2016
Abigail Curtis, a postdoctoral fellow at the American Museum of Natural History in New York, demonstrates how computed tomography reveals unexpected scientific insights into bat physiology.
Abigail Curtis, a postdoctoral fellow at the American Museum of Natural History in New York, demonstrates how computed tomography reveals unexpected scientific insights into bat physiology. X-ray with computed tomography is used to create digital reconstructions of modern and fossilized bat samples. These images enable research into how bat species have developed specialized anatomy for eating, communicating, and locating food. Most importantly, researchers are using non-destructive testing methods to share digital scans of bats to collaborate on a global scale.
Micro Bats and Mega Bats
This talk includes an overview of the various types of bats and the types of samples that are collected by biologists. You won't believe the incredible diversity within this group of mammals, with specimens that range from many kilos to a bat that is smaller than the tip of your thumb. However, bat physiognomy is remarkably similar across species, yet uniquely specialized to emphasize different functions.
Watch a 25-minute video to learn some fascinating things about CT, as applied to the life science of bat research. You'll see how researchers found anatomical structures that were isolated and studied separately from skull CT images. Abigail also discusses how researchers were able to use the CT image data to collaborate from various locations around the world.
Examining Bat Evolution
Bats are actually the second most diverse group of mammals. So, next to rodents, which have about 2,000 species, bats have between 1,300 to 1,500 species and they all just get weirder and weirder the harder you look through the list of species. When you get underneath at what their faces look like and look at the bones, you see that the structure of the bones is also really different among species.These structures or these differences relate to how they use their skulls.
Bones are basically fancy physics. It's physics applied to bones. If you break these skulls down into this back area (red in the image on this page), which basically holds the brain, and the front area in blue, which is the snout, the actual proportion of the snout relative to the part that holds the brain reflects how they use their skulls. So the guy on the right eats hard fruit. And you can see these kinds of principles when you think about dogs. You would rather get bitten probably by a collie than you would by a pit bull, and they have very different shaped snouts. We can kind of think of that logically in domestic dogs. This guy on the left is somewhat like a hummingbird, and he feeds on nectar. So it has a really long skinny snout, it doesn't need to crush hard fruit seeds. And the one that's kind of intermediate is also an omnivore. There's a lot of diversity in the range of lengths that their skulls can take. These are the types of things that really fascinate me as a biologist.
Using Computed Tomography to Examine Bat Skulls
This is my new favorite picture. So, all the cool kids now in biology are doing soft tissue X-ray CT examinations. So this bat here (image at right) looks like it got into a bag of Cheetos, but it's actually a nectar feeder. It got its face inside of the plant and got pollen all over its face. With CT scans, and you can see a lot of really interesting things about the tissue, including the brain, and specifically, the cerebellum, which is involved in balance and perception of movement. We can see density variations on the brain, nasal chamber features, soft tissue lining, and then also the muscles surrounding the skull.
What you can do with these scans is you can go through and get these soft tissues out and place them back on to the bone. In this image (at right) a bat skull with the jaw closing muscles here in red and blue, and this is the jaw opening muscle here in purple. And so then you can start to understand how are the muscle fibers are oriented, how do they change orientation if you scan a bat that has its mouth closed versus open, how does it compare among different types of mammals.
In this last image (at right), we have a bat type of carnivore, a weasel-like animal, a shrew, and a type of rodent. Maybe something like a muskrat type animal, but a little bit smaller. So you can look at how these different parts of the muscles differ in proportion among species. For something that's feeding more on plants, it's emphasized more of this blue muscle. Whereas this guy (shown in the upper right of the four animal views), that's feeding on really hard fruit and needs to have really high bite forces with its mouth wide open, has a really big red muscle here attaching to the top. So you can start to understand the evolutionary patterns in the jaw closing muscles and how that relates to feeding.
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