Geoscience Reference
In-Depth Information
Interpretations of these pedal oddities, which paleontologists had noted since
the19thcentury,havebeenquitevariedandinclude:(1)bettertractiononuncertain
terrain, kind of like how snow tires or treads on running shoes are used for the
same function; (2) use in defense, in which a kick from a massive leg with huge
curved claws would devastate a theropod attacker or sauropod rival; (3) use in mat-
ing (more about that later); and (4) digging out nests. Fortunately, with regard to
digging, no one has seriously offered the idea that sauropods burrowed, in which
theirlongnecksmighthaveservedasperiscopes. Instead,thephrase“diggingsaur-
opods” implies that they merely scratched a surface and never got too deep.
To test the “scratch-digging” hypothesis, two paleontologists, Denver Fowler
and Lee Hall, followed up on Jackson's and others' discovery of sauropod nests in
Argentina by more critically examining the rear feet of sauropods, as well as how
living animals make ground nests. In their paper published in 2009, they proposed
that many sauropod feet were perfectly adapted for digging out nests. A creative
aspect of their study was to completely reject the “elephant foot” comparison, and
instead look at the feet of much smaller modern tortoises. Once size is discounted,
the foot anatomy of some sauropods and tortoise species are remarkably similar.
This was an intriguing clue, because some tortoises, such as the gopher tortoise of
the southeastern U.S. (
Gopherus polyphemus
), are magnificent burrowers and can
make twisting 5 to 10 m (16-33 ft) long burrows. More important, though, females
use their rear feet for scratching out their ground nests in which they lay their eggs.
To get a better idea of how sauropods might have dug out their nests, Fowler
and Hall read many accounts of tortoises digging nests and watched videos of tor-
toises making nests, noting the following sequence of motions:
• Finding the right spot with suitable sediments for digging a nest, which
sometimes was aided by the tortoise urinating onto the sediment to loosen
it;
• Digging a small “starter” hole with the front feet, which does not always
happen but can be part of the process;
