I talked with Dr. Olsen about the research. Our conversation has been condensed and edited for space and clarity.
What is your research about?
I study the evolution of motion in vertebrates.
Why largemouth bass?
They’re easy to get, and bass are powerful suction feeders, which was of interest to Ariel and Elizabeth. And there’s been a lot of work previously on largemouth bass.
How do you get such clear reconstructions of the moving bones in a fish mouth?
We implant little metal beads in the bones and then film the fish from two different X-ray views. With X-rays, we can see how the bones are moving. Then we CT-scan the fish and align each scanned bone with the X-ray video, using the beads as anchor points. So the reconstructed motion you see is actual live motion.
You found these four more or less rigid bones are connected by joints with three degrees of freedom. What’s a degree of freedom?
You can think of degrees of freedom as the number of different ways you can move something. For example, a hinge has one degree of freedom while a ball-and-socket joint has three.
Why bother to study this?
Fish heads are a great model for understanding how joints work and how bones move. And biomechanics researchers have collected motion data from many other species, including, pigs, birds and turtles. So one of my goals over the next few years is to link the shape of different joints across animals to the motion we see at those joints.
Human joints in a diseased state may resemble nonhuman joints, such that exploring the diversity of joints among animals may actually be informative for human joint diseases. I don’t know if that will be the case, but I think it’s worth exploring.