What is a fossil?

NARRATOR: What is a fossil, and how is it different from a regular skeleton? 

BENSON: A fossil is any remnant of past organic life. So for example, a bone or a tooth. But also any trace that it left in the sediment. Dinosaurs’ footprints are fossils, or the trackways of other animals.

NARRATOR: There are fossilized plants and shells, and even fossilized chemical traces of past life.

BENSON: Also fossil poop, of course. [LAUGHING] 

NARRATOR: Yup, there’s even fossil poop.

NARRATOR: A fossil bone has typically undergone a process called fossilization between when the animal died, and when the fossil was found by today’s paleontologists. 

BENSON: So fossilization typically involves original mineralized parts of organisms like shells and bones. And those are mineralized structures in the original animal, so they don’t decay after death, but they often get a bit altered. Through time, water’s flowing gradually through the rocks. Bone is a really porous, spongy material, and waters deposit new minerals inside all of the void spaces in the bones.

NARRATOR: Or water may dissolve a bone or shell completely, and deposit new minerals in the same shape, like a mold and a cast. These new minerals are the reason that a fossil might be a completely different color, like brown or green, instead of white. So after this process, fossils are basically just rocks–which can sometimes make it hard to tell them apart from all the other rocks you might find at a fossil site.

BENSON: In fact, I’m sad to say that I’ve sometimes collected things I thought were fossils that turned out to be some other minerals that were the same colors as the fossil bones. So some of the key things we look out for is, firstly, does it really look like a bone, as in is its structure similar to the structure of bones. And if it really looks nothing like a bone, then it probably isn’t one. That spongy texture of bone can cause it to stick to people’s tongues. So some paleontologists like to lick the bone and see how sticky it feels to them. Myself, I don’t like this technique very much.

NARRATOR: And while you might think it would be pretty hard to miss a full T. rex skeleton lying out on the sand, remember that most of the bones that make up an animal don’t actually make it to the fossilization process.

BENSON: After an animal dies, its remains might be around on the surface for quite some time. And in that time, lots of different things can happen. Like it can be washed around by waters, or it can be interfered with by scavengers. So what that means is many of the fossil remains of past animals that we find are just parts of the animal. So they might be one bone or one tooth or even just part of one bone. It’s actually quite rare that we find complete skeletons, and we’re lucky to find even most of the skeleton or half of the skeleton.

NARRATOR: And all those other types of fossils that don’t contain hard parts–chemicals, fossilized muscle or skin, or footprints–are even more rare. But when we do find them, they tell us so much that just a skeleton by itself, can’t.

BENSON: In dinosaurs, this has been particularly exciting, because we have fossil dinosaur feathers. And this tells us a lot, you know? Dinosaurs weren’t just scaly reptiles, they’re related to birds. If we’re lucky to get the keratinous sheath of claws preserved, we can know a bit about what the appearance of what the actual claws of an animal would have been. 

NARRATOR: Or beautiful amber, formed by mineralized sap from trees, can show us fully preserved insects and beyond.

BENSON: Insect fossils can be quite common in amber, but also things like small reptile scales or bird feathers or the feathers of small dinosaurs. And we also very rarely have had parts of lizards that are trapped in amber. And this really provides a truly exceptional window into like the remains of animals that we just couldn’t see otherwise.

NARRATOR: Today, advancements in science mean we can even find fossilized molecules like ancient DNA and proteins, expanding the questions paleontologists can ask about past life.  It’s amazing that our dynamic planet has preserved so much of the history of life, because every fossil is the result of lucky circumstances.

BENSON: Getting into the fossil record is a little bit like winning the lottery. 

NARRATOR: There are a few things that can improve the chances of a fossil surviving until the present day. When this trilobite died, its exoskeleton landed on the ocean floor, a place where sediment builds up faster than it’s eroded away, allowing preservation and fossilization to occur. But not only did it become a fossil, but this fossil managed to persist undisturbed in the rocks for hundreds of millions of years. 

BENSON: If an animal dies somewhere where the earth’s crust is gradually being stretched, that stretching causes the surface to come down forming what we call a sedimentary basin, where the rocks will survive on earth’s surface for a long time. 

NARRATOR: And voila! Evidence of an animal from 450 million years ago that scientists can study for many generations to come.