Kids' Paleontology: Fossils

This class was all about the fossils! First up was impression fossils.
 
The first kind of impression fossils are fossilized imprints of relatively flat things like feathers, leaves, or fish.  I have only a few of those: this tiny fish and some ferns.

We made our imprints on a shallow pool of plaster (on a plate) with the kids' choice of feathers, ferns, or snake skin. Spray the plaster with cooking spray before you make the impression, then leave it on for about 15 minutes.

Mold and cast fossils are, in a sense, deeper imprints.  The animal or shell gradually dissolves, leaving an impression that fills with mud turning into stone.

We have lots of examples of these, including most of our shells and all of our trilobites.

This time we used plaster in a cup impressed with real ammonites (our fossil gift for this class).

I didn't have time to do the second part of this, but, after we removed the ammonite, we had a mold left in the plaster.  We could have sprayed the mold and made another plaster cast from the mold, but we would have had to wait until the first plaster had cured enough to do that (maybe a day or so).

The third kind of impression fossil is trace fossils: leftover traces that aren't the original animal.  These include things like footprints, burrows, coprolites (fossilized droppings), eggshells, or gastroliths (stones the dinosaur swallowed to grind the plants they ate since they didn't chew).

I only have one of this kind of fossil, a rather unimpressive looking worm burrow!  But I did use toy dinosaurs to make tracks in clay.

In the picture there are 4 dinosaurs.  Can you identify which ones are dinosaurs and which traces belong to which of the 7 animals?

We also talked a bit about preserved fossils like coal, amber, and frozen wooly mammoths.

But the fossils most people think of are the mineral replaced or permineralized fossils. These include bones and teeth like this whale vertebra, dolphin jawbone, and megaladon tooth.  It also includes all the shark teeth we collect!


To show how this works, I demineralized a chicken bone by soaking it in vinegar for about a week.
 With the calcium dissolved out it gets all rubbery!

In a bone buried in soil, water leaches minerals out over time, but it also adds minerals from the surrounding soil.  This is what gives fossils their different colors, depending on what surrounds the bones, as well as they their hardness.

I also had cut out a bunch of "bones" from sponges and had the kids soak these in a solution of epsom

salts.  I showed the kids the dried salt crystals (and we talked about why it's A salt, but not THE salt), before we started.  At the next class, a week later they, were hard and white!  I had them feel a regular sponge, their "bone" sponge, and a real regular bone and a real fossilized bone.

OK, yeah, maybe I am crazy.

In case you're wondering where I'm getting all the bones, I keep a bunch of bones  from chicken, ham, beef and pork ribs, and lamb.  I clean and dry them, then store them for experiments like this.  The Zoomlians also collect (and carefully bleach) a variety of bones they've found while hiking. 

The bone collection probably sounds crazy, but it has been super useful in teaching biology, anatomy, paleontology, and any number of random wonderings.