Geoscience Reference
In-Depth Information
growth from a small chick to a full-sized roaster. In other words, relatively long
strides measured between tracks made by a small-footed and short-legged animal
implies it was moving faster. Alexander's formula was also based on modern an-
imals, in which he used measured speeds, body masses, and stride lengths of many
two- and four-legged animals to establish a baseline for comparing these to dino-
saur trackways.
Fortunately, there is a simpler way to express this equation and get a quick-
and-dirtysenseofwhetheradinosaurwaswalkingslowly,trotting,orrunning.This
is to look at stride length versus hip height as a ratio, called
relative stride length
.
As an example, let's take our previously mentioned theropod with the 35-cm long
footprint and 1.4 m hip height. Let's say its stride was measured as 2.8 m (about 9
feet). So its relative stride length is 2.8 m/1.4 m, which = 2.0. Basically, Alexander
proposed that relative stride lengths of 2.0 or less reflect walking, 2.0-2.9 trotting,
and >2.9 running. This means our hypothetical theropod was likely walking. Using
the full formula, this corresponds to a calculated speed of about 3 m/s, or 10.6 kph
(6.6 mph).
How fast is that in practical everyday terms? Olympic racewalkers regularly
exceed 15 kph, which they can keep up for 20 km (12.4 mi). However amusing it
mightbetovisualize, agoodracewalker wouldcrossthefinishlineofa20-kmrace
a half hour before our imaginary dinosaur. Even more entertaining, human race-
walkers would have even outpaced huge dinosaurs—such as sauropods—with leg
lengths more than double the heights of those people, as their trackways also indic-
ate slow speeds for these dinosaurs, too.
Nonetheless, let's go back to that theropod trackway and follow it for a while.
Along the way, you might notice its stride increased to a maximum of, say, 4.0 m.
Consequently, its relative stride increases to 2.9. Now we're talking “run,” and the
calculated speed would be 5.3 m/s, which is about 19 kph (12 mph). Our Olympic
racewalkers would badly lose a race of any distance to this theropod, and many
well-conditioned runners would too.
