trackway gauge and speed

["Emma C. Rainforth" <emmar@ldeo.columbia.edu>]

Title: trackway gauge and speed

Without going into a discussion of the paper in question:

Looking at 'theropod' tracks from the Connecticut Valley (Newark Supergroup in part; Late Tr-Early Jur.): pick an ichnotaxon, any ichnotaxon, and look at a number of specimens, showing different relative stride lengths for a given footprint length. (i.e. a longer relative stride indicates the critter moved faster, right?)

okay, from my observations, from a 'single sample' (Early Jur., Conn valley - so as not to compare Hettangian theropods with Cretaceous ornithopods), 'speed' does not influence trackway gauge ('width').

Now, run (and walk) an experiment.

Walk (yes, you, Homo sapiens, an extant biped) in a straight line. Now run in a straight line. Preferably on a substrate that will 'preserve' your footprints. Failing that, stand in a pool of paint first.

Look at your trackway. Hmm, I'm pretty sure you'd have to call it 'narrow gauge'. Regardless of your actual speed. To make a 'wide gauge' trackway is pretty hard - you basically have to waddle, and you're very off-balance, right? (You also don't get very far very fast!) Sure, the gauge may vary a little - when you run, your feet are slightly more in line than when not. But even so, it;s not a huge variation.

I've not even SEEN a 'wide-gauge' trackway of ANY biped from anywhere in the Newark Supergroup (North Carolina to Nova Scotia; oh, the sample size is pretty big, too....many hundreds of specimens). Suggests bipeds prefer to walk narrow-gauge. But, unless you have been confined to a wheelchair your entire life, you pretty much experienced that for yourself, every day, right? Wide-gauge, thus, should be considered  unusual behaviour. Such trackways show what the critter CAN do, on occasion - but it is not 'normal' (seeing as 99.99999% of bipedal dino trackways - a ballpark figure! - are narrow-gauge. So, using that data (a single example) to extrapolate across-the-board is not the most parsimonious (smartest) thing to do.....

:-)

IMHO: to say 'narrow-gauge = fast, wide-gauge = slow' is correct, but, bear in mind that this statement omitted 'narrow-gauge= any speed'.

emma