Rolling with dinosaurs

After Chalking With Dinosaurs with Burnsy on BBC Radio Humberside this week, I intended my next post to be on the Megalosaurus trackways of Oxfordshire. However, my better half then showed me this video:

We immediately found ourselves thinking: “That would be cool with dinosaur feet!”

Then we thought “Actually, it would be cooler with correctly sized dinosaur feet that could produce some sort of trackway…”

So this is what we did…

1) Get together all the kit you might possibly need (different sized tubes for rolling, cardboard for making feet with, pens and pencils, tape measures, scissors, cocktail sticks/kebab skewers to attach the feet to the rolling tube).

All the kit you need to make a rolling dinosaur foot trackmaker!

2) Decide that the smallest tube needs to be an ornithopod, the medium-sized tube a theropod, and the largest tube a sauropod. Measure the diameters of the tubes to work out the ‘hip height’ of the dinosaur (the fully extended length of the leg when the foot hits the ground), and divide that number by 4 to come up with a proportional size for the foot.

Tube diameter (leg length) = 45 mm, so foot length = 11.25 mm

Tube diameter (leg length) = 94 mm, so foot length = 23.5 mm

2b) Then remember that sauropods aren’t quite the same as ornithopods or theropods, and consult a paper by Bernardo J. Gonzalez Riga to come up with some better-looking numbers. Decide to save the sauropod rolling trackway making for next time.

3) For a bit of ancestral accuracy, use the feather of an extant theropod to colour in the tiny feet of your rolling theropod trackmaker.

4) Cut out the feet, tape each of them onto a short bit of cocktail stick, then tape them to the inside of the rolling tube. Then realize they’re not thick enough to touch the ground when the tube rolls, so take them off again and add more card until they are. We did this for the ‘ornithopod’ on the small tube, though the challenge of cutting out small cardboard feet accurately means they are best described simply as tridactyl.

5) Find a reasonably large tray and cover with some kind of soft sediment. In this case, I used gardeners’ silver sand, but I’m sure flour or salt or sugar could work.

6) Roll the foot-bearing tube across the sand to see if it works, and – hey presto! – a dinosaur trackway. Yes, ok, it’s a one-legged dinosaur with an implausibly wide gait, but this is a work in progress!

A dinosaur trackway made in fine-grained sand by a rolling tube on my kitchen table. Fossilization potential: low.

7) To work out how fast the dinosaur was moving, measure the stride length. Here it was 150mm, give or take:

Trackway stride length, measured from heel to heel.

8) Divide stride length by leg length to get the relative stride length (RSL). If the RSL ratio is 2 or less, it is walking. If it is 2.0 to 2.9, it is trotting, and if it is 2.9 or more, it is running. The measured stride length here (150 mm) divided by the leg length (45 mm) yields an RSL value of 3.33, which means…

(I’m not aware of any evidence from the trace fossil record of tiny, wide dinosaurs hopping at high speed, but at least now we know what kind of trackway we’re looking for.)

Another – probably more genuinely ichnologically useful – thing is that, even with just two footprints made by the same cardboard foot in uniform dry sand, we can see that there is variation in track morphology. The second footprint is a much more accurate representation of the cardboard foot than the first one.

Footprint 1 of the tiny rolling dinosaur trackway.

Footprint 2 of the tiny rolling dinosaur trackway.

I will write this up as an activity sheet in due course, and get back on with chalking those dinosaur trackways, like I promised.