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Episode 3: How Do You Know If It Is A Fossil?


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.

Last time we talked about how paleontologists prospect to find fossils. Prospecting is where we walk around slowly, looking for scraps of bone that have weathered and eroded out of the ground. 

One of the most common questions we get is “How can you tell the fossil bone from the rock? And that can be pretty tricky. So let’s start digging into that question right now.

There are lots of different features we use to figure out if something is a fossil or a rock.  Shape is the most obvious.  If something looks like a bone or a tooth, it probably is.  But what we usually find is a fragment of a bone or tooth, not of a whole one, so the shape isn’t always the most reliable feature. 

But what about the color?  Fossils are almost always a different color than the surrounding rock. In this case, we have some black, whites, and even some orange, and as you can see, they’re very different than all the surrounding grey gumbo.   

Texture can be an excellent hint.  Some bones, especially turtle bones like these we’ve been working on, have an unusual texture, or surface pattern. As you can see, this piece has a very clear pattern on it, and you wouldn’t expect to see a pattern like that on the surface of a normal rock. Pretty much all other fossil animal bones are nice and smooth on the outer edge, just like modern bones.   

Now, if texture doesn’t give it away, then this next hint is a dead ringer almost every time. As you can see, even in these little pieces of fossil, there are a lot of pore spaces, just like we have in parts of our bones. In fact, we call this “spongy bone.” These pore spaces often preserve very nicely, as you can see in these specimens. Those pore spaces aren’t just in our bones - they’re in the bones of all animals, even animals that lived millions of years ago. That similarity suggests to us that we all must have inherited that feature from a common ancestor that must have lived hundreds of millions of years ago. 

Sometimes, though, you can’t even be sure about those pore spaces.  Lichens growing on the outer surface of the rock, or the rock’s colors can fool you.  So, there’s one last trick you can use that is absolutely foolproof  every single time - you lick it!  No, fossils don’t taste different from rocks. The idea here is that if these really are pore spaces, then they would soak up any moisture through capillary action, creating a little bit of suction. So, if you lick it and sticks very slightly to your tongue, then it really is a fossil. Let’s see.

All of this is actually a lot easier than it might seem. If you were out here with us, you could use these tricks of the trade to find fossils within a just few minutes. And after a short time, you’d develop a mental image of what you should be looking for, and then, well . . . you’re home free, because you’ll start finding fossils everywhere!

So far we’ve shown you where to look for dinosaur fossils, how to look for those fossils, and now how to tell the actual fossils from the surrounding rock. But what then? If we’re lucky enough to find a nice skeleton in the ground, how do we get it out?  Well, we’ll start digging in to those questions next time. Until then, thanks for joining us, and as always, keep digging!