Identifying the CAPacabra (Part 1)

Hi!

My name is Jerielle and I’m a first year CAP fellow, working on my PhD in forensic anthropology. I have an undergraduate degree in biology and a masters degree in forensic anthropology. Unlike many other CAP fellows, my interests lean more towards (human) skeletal anatomy and development rather than historical artefacts. Fortunately, we do have one mysterious animal haunting the CAP lab.

Meet the CAPacabra

The CAPacabra is a mummified animal that was discovered in the ceiling of Cook Hall in May of 2018. Cook Hall was first built in 1889 as the Entomology Building of “Laboratory Row” on West Circle. It was named Cook Hall in 1969 after Albert J. Cook, a prominent entomologist who graduated from Michigan Agricultural College (now MSU) in 1862. In 2018, the building was renamed the Cook-Seever Hall, in recognition of MSU graduate Gary L. Seevers who donated $3 million to support the building’s renovation. This renovation added an elevator and accessible entrance, as well as restoring the ceilings, walls, and lighting. It was during this renovation that the CAPacabra was discovered.

Otherwise, we don’t know much about our mummified friend! In fact, what animal it even is has been debated. Although there is a 3D model on SketchFab calling it an opossum, others argue it may be a large rat, or even a small dog or cat.

Join me as we try to find out what the CAPacabra really is!

There are two parts to finding out what animal the CAPacabra is: gross (large-scale) anatomy, and radiographic (x-ray) analysis.

The CAPacabra is a quadruped, approximately 1 foot long including its tail. The tissues that remain are extremely dry and brittle, with a texture more similar to old leaves than actual skin. What’s particularly interesting to me is that our friend is hairless. While it’s not surprising that they would have lost their hair over the years as the soft tissues dried, I would have expected some traces to remain behind in the ears or other small crevices. This was not the case!

In some places, the dried tissues have flaked away to show the underlying bones. Between these exposed bones and the remaining teeth, we can get a rough estimate of the animal’s age. And once we know if we’re looking at a juvenile or adult animal, we can do some comparisons to see which of our contenders are (or are not) possible answers.

Age Estimation

Bones grow with the individual, so they develop in separate parts which fuse when the animal has reached skeletal maturity. In humans, we can use this epiphyseal union to estimate the age of the individual. I don’t need to know what age the CAPacabra is specifically. Instead, I’m looking for fused bones (reached skeletal maturity) versus unfused bones (did not reach skeletal maturity).

We have two lines that are visible through the remaining tissue. The first (left) is at the distal end of the tibia (shinbone), while the second (right) is the distal end of the femur (thigh bone). Both of these lines are really close to fusing, but they’re still visible. This means that the CAPacabra was close to, but didn’t quite reach, skeletal maturity.

Another thing we can look at is dental development. Just like humans, animal dentition develops as they do. An animal with close-to-adult bones should have close-to-adult or even fully-adult teeth. There appears to be a mostly full set of teeth present. Of course, I’m not a zoologist, so while I suspect these are adult teeth, I won’t know until we get to the radiographic analysis. There is always the (slight) possibility that they are deciduous teeth and the permanent dentition just hasn’t come in yet.

This is a pretty slim chance though, and the reason why is…we have a second CAPacabra! Our completely mummified friend here was not the only mummy recovered from the ceiling during the restoration. We also have the mummified skull of a similar animal. I’m going to make a judgement call and say: similar dentition, similar ears and facial structures, recovered together from the same building at the same time? They probably are associated, and we can probably work under the belief that they are the same species. Which means that we can use CAPacabra Junior as a reference for what juvenile dentition would look like: there are several teeth just peeking out behind others in figure 3 (right image, red arrows), which tells us that this particular individual was still losing deciduous teeth (aka milk teeth).

Species Identification

Why do we want to know a general age in order to figure out the species? Some animals (including humans) have juvenile bones that can look quite different from the adult version, but a lot of comparative osteology reference texts use images of adult animals. I want to make sure I’m comparing apples to apples.

For the gross comparison, I’m consulting Comparative osteology: A laboratory and field guide of common North American animals by Adams and Crabtree (2012). This field reference gives images of common animal bones for comparison. We know that the CAPacabra is pretty small, so dog, raccoon, opossum, and cat were the most relevant. What’s really cool is that they also have comparative images online, so you can check them out too!

The CAPacabra has sharp carnivore teeth and a high, pronounced forehead. The opossum has a much pointer snout and maxillae, along with smaller teeth overall. It’s probably not an opossum, despite what we’ve been guessing for years. Cat skulls are actually really small and blunt, with very reduced maxillae meaning almost no actual snout. They also have much fewer teeth than our mystery fried. It’s probably not a cat. While the Adams and Crabtree (2012) text doesn’t have rat skulls for reference, the CAPacabra would have to be a real ROUS to be a match for our individual.

Which leaves dog and raccoon. The skull that Adams and Crabtree use for the raccoon example is missing a lot of dentition which I would have liked to use. So while the slope of the forehead isn’t quite right here, I don’t want to rule out raccoon just yet. I also can’t rule out dog, since the teeth have similarly sharp cusps, and the forehead is similarly sloped. The point that I’m stuck on at the moment is the fact that the CAPacabra has more of an angle to the forehead than our raccoon example, but is missing the sagittal crest in the dog example.

Next Steps

My next step is to take some xrays of our CAPacabra. I don’t think I can see enough of the postcranial bones to make a more definitive call from just the gross anatomy. I especially want to look at the skull for dentition and the presence (or absence) of that sagittal crest. I also want a closer look at the front paws, because those seem more like raccoon hands than dog paws.

But I am happy at this point that I can tell fellow CAP members that they are wrong about it being an opossum. Raccoon makes sense as a match for our friend, since they’re more likely to find their way into weird places, like a ceiling. If the CAPacabra ends up being a dog, I have some serious follow-up questions.

What do you think? Are there any other species I should consider? Is there something I should reconsider?

Look out for Part 2, where I’ll report on the results of the radiography!