Chalking With Dinosaurs, part 3

On Saturday May 9th 2020, as promised, I chalked a load of dinosaur footprints onto my driveway.

Two cardboard cut-outs of Yorkshire dinosaur footprints, and some chalk.

My video below explains what I did, and what a single footprint can tell us about the tracemaker. WARNING: this video features some low-quality singing.

If you want to go chalking with dinosaurs, here’s my checklist:

1. Choose a footprint you want to chalk. I decided to start with the big Burniston footprint described by Martin Whyte and colleagues in 2006. However, you might want to chalk a completely different dinosaur footprint, or your own footprint, or invent the footprint of a creature even more fantastical than a dinosaur.

2. Draw the footprint onto a piece of card and cut it out, to keep your footprint chalk drawings consistent.

My cardboard version of the big Burniston footprint (Whyte et al. 2006), with the interpreted size of the dinosaur foot highlighted, and my left foot shown for scale.

3. Get your chalks, work out where you want your footprint to go, and start drawing. If you don’t have a driveway, an alleyway or a yard will do just as well. If you don’t have outdoor space for chalking, draw the footprints onto paper indoors.

4. Measure the footprint. Is it the same size as the tracemaker’s foot? This can be quite hard to determine from a trace fossil, but the answer is often no. Martin Whyte and colleagues decided that, although the large Burniston footprint was 0.61m long by 0.49m wide, the squidgification* around the edges of the footprint suggested that the dinosaur foot itself was probably 0.55m long by 0.40m wide (hence my annnotation in the figure above).

*technical term

5. From the size of the tracemaker’s foot, you can then estimate the size of its leg. How? Well, take some measurements of your own leg. My foot is 0.265m long, and my hip height is 0.91m, so that gives a ratio of hip height (h) to FL (Foot Length) as follows:

h = 3.43FL

If that ratio was true for the Burniston dinosaur, its foot length of 0.55m would yield a hip height of 1.89m (which is taller than me!).

A Tyrannosaurus rex and a 1.8m tall human (image from Wikimedia Commons). I am 1.8m tall.

6. However, I am not a dinosaur. It is much better to use measurements made from dinosaur skeletons. R. McNeill Alexander did exactly this in the 1970s and came up with a slightly different equation for dinosaurs:

h = 4FL

That would make the hip height of the big Burniston tracemaker 2.2 metres, which is taller than most humans.

7. Unsurprisingly, then, the big Burniston footprint was made by a big beast, but what kind of beast exactly? The three-toed (tridactyl) print with a V-shaped heel and distinct claw marks strongly suggests it was a theropod (hence the title of Whyte and colleagues’ 2006 paper). However, there are no Burniston bones to confirm this, and no skeletons of Middle Jurassic theropods are known from Yorkshire. So what kind of theropod was it?

Examples of some of the largest theropod dinosaurs (image from Wikimedia Commons).

For that, you’ll have to wait for Chalking With Dinosaurs, part 4!