Tracing respiratory structures

Jen here-

Cartoon blastoid cut in half so you can see the inside of the specimen. Each slice in the video is taken horizontal to the longest axis of the specimen. Figure modified from Dexter et al. (2008)
As I briefly discuss on my research page, here, part of my main research focus is to better understand respiratory structures of extinct animals. I’ve embedded a video on how I actually go about doing this. I’m using acetate peels to trace the structures through the body. These are essentially thin slices that allow us to section or take pieces of the fossil bit by bit. There is a general agreement about where the respiratory structures of blastoids (called hydrospires) connect to the exterior of the body. This means I can find this location on the inside to find the structures.

Once I have identified the structures, I can trace each one! I use a drawing pad and it can actually be quite relaxing tracing the folds. But it takes a lot of time and we have thought about figuring out how to make the computer do it for us but in some cases the outline is faint or you can see extra folds that are not actually part of the layer you are on. This happens when the slices of the fossil are taken not exactly perpendicular to the long body axis. The slices that I am working with were made in the 1960s and were done by hand so it is common that they are not exactly perpendicular.

In the video below you can see me tracing the hydrospire folds on a slice of Pentremites pulchellus. Once we trace all of the folds we were interested in, we can hide the images of the slices and all that remains are a series of stacked line drawings. We use another program to create the three dimensional structures.

Citation: Dexter, T.A., Sumrall, C.D., and McKinney, M.L 2008. Allometric strategies for increasing respiratory surface area in the Mississippian blastoid Pentremites. Lethaia, 42, doi: 10.1111/j.1502-3931.2008.00110.x

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