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Episode 8: Which Dinosaur And Part Of The Body Does That Fossil Belong To?

Transcript:

Welcome back to the New Jersey State Museum’s Ask the Experts Video Learning Library, where we’re digging into some of the most common questions people ask paleontologists about what we do and how we do it. The last time you joined us you learned all about how we separate the rock from the bone, and how we clean them. Now we’re left with some nice clean bones, but… now what?  Where do we even begin?  What animal is this, and where does it belong in the animal’s body?  Well, let’s start digging into those questions right now. 

The first thing we need to do is figure out what bone we have.  This is one area where there really is no substitute for good old-fashioned, hands-on learning.  Paleontologists spend a lot of time looking at, and studying the skeletons of different animals.  Skeletons really are fascinating, because they have many functions.  First of all, they hold up our bodies. Secondly, they also serve as attachment sites for soft tissues, like ligaments, tendons and muscles.  Every shape and feature of a bone can give you hints about those soft tissues, if you just know how to read them.  This is really important, because those soft tissues almost never, ever get preserved.  So, if we want to know more about their bodies and how these animals lived then we have to know how to read these bones.

It doesn’t matter if you’re looking at the skeletons of completely unrelated animals, just about all tetrapods have the same basic body plan, or skeleton.  For example, you and I have an upper arm bone , ribs, and a series of vertabrae that protect our spines.  Well, so do whales, turtles, and deer.  And it’s not just that we have the same basic body plan - each of these bones have distinct similarities across all those different animals groups.  For example, ribs from just about any animal are generally long, gently curving, slightly tapering and rather simple bones, and there just aren’t many other bones in the body like them. On the other hand, vertebrae from all different animals almost always have a centrum, that is shaped like a spool, have a ball or socket joint on each end, and have a rather complicated structure above. A humerus is generally a long bone with a ball that forms the shoulder joint, and then condyles at the other end that form the elbow joint. These bones are from completely different animals, but they all have these same general shapes and features.  Once you’ve seen enough of these bones and structures in one species of animal, you’ll start to recognize them in other species of animals. So even though dinosaurs and deer lived millions of years apart, their humerii or upper arm bones still have a lot of similarities.   

Ok, so that’s how we figure out what bones we have, but how does this help us figure out what animal those bones came from?  Well, it’s generally safe to assume that species within a group have skeletons that are more similar to each other than skeletons of animals from different groups.  Think of it this way - there are lots of species of turtles out there, and each one has a slightly different humerus shape.  But, in general, all turtle humeri look more similar to each other, than they do to the humerus of a deer or bird. The general features of these bones tell us they are humeri, but if we’re familiar enough with the features of a turtle humerus, deer humerus, or a dinosaur humerus, we can use that to figure out which group of animals these bones belong to.

So we use these features, and similarities, to help us narrow down which group of animal any particular bone may have come from. Some bones are very characteristic, and we can tell right away exactly what species it came from. Other bones, though, don’t have very many features and don’t tell us much at all. Very often when we’re in the field we find bones or pieces of bones that we can’t identify at all, other than to just say that it came from a dinosaur.   

Very simply, that’s how we study the skeletons of dinosaurs, and how we figure out what dinosaurs the bones belong to. Over the years, paleontologists have found thousands and thousands of bones, from hundreds of different species, so we have a really good idea of what many of their skeletons look like. But, there’s still only so much the bones can tell us.  What if we want to know things like what did they look like when they were alive?  What colors were they, and what did their skin look like?  How could we possibly ever even know any of that? Well, we better start digging into those questions next time. Until then, as always, thanks for joining us, and keep digging!