Look! Up in the sky! It's a bird! It's a plane! It's a...um...It's an.....er....I mean....It's......uh, what the hell is that thing?
Silly people. It's called a ruler. Or, is that too scientific for some of you? We could call it a measuring stick. But there's a lot of vowels in 'measuring', so let's lust call it a stick with marks.
Welcome to Friday Rocks. Today is the day we learn about fossils. Or, to use the less scientific term, 'rocks with dead stuff in them'.
The fossils aren't always in the rocks, though. (remember from back a few weeks, the rock the fossil is in is called 'matrix'). Depending on the type of fossil, and the level of it's preservation, it can sometimes be removed from the matrix to become a free-standing fossil. Examples of fossils that have been released from the matrix would be the bones of animals you see on display at a museum.
Trilobites aren't generally totally removed from the matrix unless they are enrolled. This is not because the specimens aren't complete, but because they are very fragile. (I know this from personal experience. My Crotalocephalus is proof of that. But that's a story for another week. Maybe next week...). Generally the trilobite will be exposed about half way. This gives them the appearance of laying prone. In truth, we have no idea how they were positioned when the died. It could very well be that they died on their back but because of the way they are prepared, they appear to be right side up.
If the conditions are right, a trilobite can be mostly removed from the matrix. That is the case with the pictured example. These are generally called flying trilobites because they have the appearance of flying. But looks can be deceiving. Not all trilobites were able to swim above the sea floor. Some spent their entire lives walking from point A to point B.
Removing a trilobite from the matrix requires skill. And time. The more detail on the trilobite, such as spines, and the level of preservation is the determining factor in the amount of the specimen that can be released. The type of mineral that the fossil is made out of also matters. Some minerals are stronger and will allow for the release more readily.
The example I have for you today is called a Paralejurus. This particular example is from the Atlas Range in Morocco. Let's take a look at it's underside, shall we? (like you have a choice...)
You can see, much of the matrix has been removed from the underside. The pleural spines are all completely free from the matrix. (the left and right sides of the thorax (body) are known as the pleural lobes and any spines attached are thus known as....pleural spines). On the right side, you can see the exoskeleton appears to be thicker. On this particular species, that thick part is actually like a shelf. It's also where the hypostome attaches. On either side of that bulge, you can make out the cracks where the librigena (free cheeks), would separate to allow the trilobite to molt. That bump at the very top? That's it's right eye.
Here's another view.
This view allows for a good example of the three main parts of a trilobite. The cephalon, (head), is the 'D' shaped piece on the right. The cephalon ends at the first segment in the thorax. (body). On this trilobite, the thorax is made up of 10 segments, each one ending in a spine. The pygidium, (tail), begins after the last segment in the thorax. If you'll remember, when I first started my series on trilobites, I said the name trilobite referred to the three parts of the bug, Cephalon, Thorax and Pygidium. These go from front to back.
But trilobites can also be separated into three segments going from right to left as well. This specimen shows it fairly well. If you look at the thorax, you can see it appears as if it is two different sections; the hump running down it's spine, and then the spines that fan out. That hump running down it's spine is called the Axial Lobe. (there is no spine). And on either side of the axial lobe are the Pleural Lobes. (you can only see the right one here). I'm sure you can tell where the dividing line between the lobes are. The cephalon and pygidium can also be separated into three lobes, but they aren't as easy to distinguish. At least, not on this example.
I apologize for not having an odd story about the natural sciences at the beginning of the post. I was going to tell the story of Marsh and Cope, but this post is already nearing tl;dr length, so I don't want to risk it. Because that's a story you really want to hear. Or read, I guess. I haven't quite figured out how to make this post into a holographic me that reads it to you. (I said holographic. Youtube doesn't support 3D holograms yet.)
So....I need to add something to this post. Something that's odd. Hmm.....I know! Here is a scientific paper on "Coaptative Devices, Enrollment, And Life Habits In Paralejurus, A Particular Case In Scutelluid Trilobites". It has a lot of interesting information init. Plus a lot of detailed pictures. The thing that makes it odd is, there are people out there, lot's of people, who read papers like that for fun. You know, the kind of thing they keep in the bathroom to read while.....you aren't going to make me say it, are you? Now, I'm not saying I read these types of papers for fun. But I did know where to find it. And I might have once downloaded the pdf....But in my defense, I thought it was porn when I clicked on the download button! I didn't realize is was edjimicashunal. (seriously though, at least try to read the Abstract. If nothing else, you'll expand your vocabulary with a bunch of words you'll have to look up the meaning of)
Now if you'll excuse me, it's time for me to finish my Friday so I can begin my Saturday.