bones in the brain

So it’s been a week. I’ve been pretty busy trying to get a thesis proposal done and I have lots of ideas for blog posts but little time to actually read a few papers and write something. This is why pop culture entries are a little easier. There was even a paper out a few days ago on differential brain development in humans and Neanderthals (check it out here) that I’ll eventually get around to talking about. But instead you’ll get this.

So a lot of this paleo/anatomy stuff is inspired by my comparative osteology class, where I come across an interesting anatomical feature and I want to know more about it. In this case, it’s the ossified tentorium cerebelli, which is generally only present in carnivores and dolphins (and weirdly, spider monkeys). Why? I dunno. And neither does anyone else according to a somewhat cursory use of GoogleScholar.

First off, the tentorium cerebelli is an extension of the dura mater (which is the outermost meningeal layer – that’s the stuff that covers and protects the brain) that separates the cerebrum and the cerebellum. These are two very different parts of the brain, with radically different textures and functions. Also,the tentorium is connected to the falx cerebrei, which is the little sheet of dura mater that separates the right and left hemispheres of the cerebrum. They make this interesting 3D structure in the cranial vault.

The tentorium and falx do not normally ossify, but enough clinical cases have been noted in humans for it to be a thing. It seems to happen especially in the eldery. This is not completely surprising – lots of shit that shouldn’t gets turned into bone as you get older.

But why is it consistently present in dolphins, carnivores, and spider monkeys? Again, no one is really sure. Just about the only thing we can say about it is that it is not developmentally homologous throughout these animals. In dolphins and spider monkeys, the bony tentorium and falx are not seen in immature individuals and only develop as the animal ages. By contrast, the bony tentorium and falx of carnivores are present even in the fetal stages of development. So, though they may seem like the same trait, they probably have drastically different causes. (if you wanna read the only helpful paper I could find on this, it’s here)

I’m not sure there’s really a whole lot else to say, partly because not a whole lot appears to have been written about it. What is it’s adaptive function? Does it have an adaptive function? Somebody‘s gotta be doing this shit. Right?

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About alexclaxton

Paleoanthropology grad student, pop culture obsessive
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