Phytosaurs and more

The phytosaur skull I found is slowly being worked on in the lab. Each day more of it is revealed from the rock by the fossil preparator. The skull still has some teeth in it, which is good… most of these skulls were rolling for a while along the bottom of a river until they came to rest, and the teeth usually snap off. Here is a picture of the skull now:

In case you can't tell, the end of the snout is toward the left, and the back of the head is toward the right. You can also see the ocular or eye-hole. I'm excessively proud of myself since it's one of the best-preserved skulls ever found here, and is the talk of the employees in the other departments, who have seen it and keep asking if I was part of the team that found it. I hear that someday it will go on display in the museum here. But it wasn't hard work to find it, I don't think.

I thought it was hard work digging it out though… my hands were all chewed up from contact with the rocks on the edge of the trench we dug around the skull… but the skull I found was in mudstone. Our supervisor found a skull the other day in sandstone, and it's been even tougher to remove. Here is our preparator using a rock saw to loosen some of the rock around the skull:

It's a big skull. You can totally see the outlines of it here:

The really crazy thing about this phytosaur is that parts of the skull are green. You can see an exposed section here:

We don't know why it's green. Perhaps it's radioactive. I happen to think "Radiactive Phytosaur" would be a great name for a band.

I mentioned that the second skull was harder to dig out because it was in sandstone. So what's up with sandstone and mudstone? They're two kinds of rock; the first is made out of sand that's been cemented, the second out of mud that's been cemented. (In between these two grades would be siltstone.) For a rock to be cemented, water has to trickle through carring some cement, such as silica. The spaces between grains of sand are bigger and so more water can come through with cement. Thus, sandstone tends to be a lot harder than mudstone.

In the beautiful badlands here, most of the hills are made of mudstone, which weathers softly. Occasionally there are bands of sandstone (marking where an ancient river channel was) and these can form cliffs.

The more pure mudstones here have what's called "popcorn weathering," a surface texture produced by the clay shrinking and swelling with the weather. It looks like this:

It forms nubbly hillsides everywhere. Here is Katie examining some mudstone; she's standing on sandstone.

When you dig a few inches into the mudstone, you get past the weathered surface, and can easily break off chunks of hardened clay that have very jagged edges and smooth sides. These are clods of ancient soils that formed on the floodplains of the Triassic. They have some fantastic colors. Here's a picture of a mottle in a clod of mudstone:

The black dot in the middle of the bullseye was probably a bit of organic matter than created "reducing" conditions in the surrounding soil; that is, it caused electrons to be donated to the iron in the soil. Iron happens to change color based on whether it's oxidized or reduced, and this causes a lot of the color changes in the beautiful badlands rocks. More on those colors later, as I promised.HHH