Dino Tracks 101

Dinosaur tracks, footprints, traces, trails... the fossil evidence left behind when dinos roamed the earth millions of years ago. You need a nice sandy or muddy surface and a dinosaur to tromp across it, then you need it to get covered and stay covered, compress under pressure and turn to rock and, finally, get exposed millions of years later.

You can see from part A that an indentation is made by the dinosaur foot in soft sediment (deepness can depend on not only the size of the dino, but how soft the mud is as well). In the underlying layers there can be undertracks, which are just parts of the lower sediment layers that receive an indent, but are not the exact surface the dino was walking on. Usually these undertracks will not be as distinct or have claw marks. The layer above fills in the track itself, and forms a natural cast, if this consists of different sediment it can form a unique cast of the print itself.

In an area with the right aged rocks you can search under overhang layers and find tracks... which is exactly what I did on my drive from Cochabamba to Torotoro, Bolivia. 

We stopped for lunch at a site of a newly built bridge. The river was trickling down the almost dry bed and snaking its way through the canyons...

The bridge itself was the only shade around, so we headed under to find a cool lunch spot. The distinct layers of sediment weather and erode differently, depending on the resistance of the sediment. Shale (ancient mud deposits) erode faster than sandstone. These shale layers break apart, fall out of the outcrop and the more resistant sandstone is left. Under that bridge last week is where I looked up and exclaimed, "Hey, those are dinosaur tracks!" Natural casts actually.

How does this happen? What is going on?

Imagine: A quick, three toed carnivore is running across a section of mud near a lake... as he runs he leaves behind footprints and in the really mucky areas he sinks deeper than in the drier areas. He's off to another spot, when the rains start. This time it's a heavy rain. Pouring. Flash floods bring sediment from the higher areas onto the mud flat and all those three toed tracks are filled with a fine sand. The storm lasts for days and the original layer is being covered by meters of sandy flow. The rains stop, the area dries out and in a few months the rains repeat and repeat and that footprint layer is buried forever. Well, not really forever, because then the continent crashes into an ocean plate and the earth rises into the air and forms mountains. These mountains are high up and this time the rains cause erosion. Chunks of rocks break off and make their way down river for more layer building, but that original layer has now resurfaced and we are ready to see it. Voila the tracks that were left 100 million years ago are now back on the surface!

If you are lucky the original surface was nice and flat and the dino left a long trail of tracks... Here you see a trackway left by an Ankylosaur type dinosaur.

Notice that the ankylosaur was not "turtle like" nor did it walk like an alligator. Dinosaurs had and upright stance with legs under the body instead of sprawled out.

Do you want another look at those tracks?

This photo was taken from outside our room at our hostel in Torotoro, Bolivia.

Notice that I said that these tracks were left by an ankylosaur type dinosaur. Tracks have their own classification system that is NOT the name of the dinosaur. Unless you find the skeleton still stuck in the footprint there is not enough evidence to say exactly which dino made the track. Instead tracks are divided into their own categories...

Can you identify the type of track from the photos?

Notice the claw mark on the middle toe. Can you see the pad impressions on the right toe? Imagine the soft mud as this therapod races across the surface.

Using my foot for scale, this is an obviously big track. Huge, roundish tracks, with a bit of overlapping between the back foot and the front foot.

Sauropods are my favorite dinos...

Whoa...

This is actually a close up of one of the tracks on a huge slab near the El Vergel waterfall in Torotoro.

Ye-haw I love dino tracks!