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• Placing her cloaca over the potential nesting spot, rear feet on either side;
• Digging with the rear feet, with each foot alternating, in which she moves
her foot to the midline of her body and pulls up a dollop of sediment on the
bottom of her foot, then places sediment outside of the hole. On the other
hand (or foot, rather), she may just fling sediment out of the hole, or she
might have saved enough urine to soften the sediment just a little more;
• Digging continues until she has made a hole about the same depth as the
length of her rear limbs. The holes differ in overall shape, but most have
been described as “flask-like,” wider at the bottom and narrower at the top;
• Once egg laying commences, she might move the eggs a bit by shifting
them laterally or pressing them down;
• After the entire clutch is laid, she buries the eggs with the excavated sedi-
ment on the sides of the hole, again using her rear limbs. The mother tor-
toise then walks away, and the eggs incubate under the enveloping sedi-
ment.
What they found out was that tortoises produced nests in a way that would ex-
plain sauropod nest building. Although the sizes and overall shapes of the tortoise
and sauropod nests are quite different—flask versus trough, respectively—their
origins are both explainable by scratch-digging. However, the whole sequence of
events just described for tortoise nesting is not a perfect fit for nesting sauropods,
either. For example, paleontologists who studied the Argentine sauropod nests do
not think these eggs were actively buried by the sauropods. Still, other sauropod
eggshellshavetherightkindofporestructureforhavingbeenburiedandincubated
under a layer of sediment, just like in tortoises. But we also presently have no trace
fossilevidenceaboutwhetheranysauropodsurinatedonthegroundfirstbeforenest
building, even though one sauropod urination trace fossil has been interpreted from
Late Jurassic rocks in Colorado, explained in a later chapter.
Thescratch-digginghypothesiswasthenfurthertestedwithsauropodeggsand
nests in Late Cretaceous rocks in Spain. Bernat Vila, Frankie Jackson, and others
looked at nine stratigraphic horizons with fossil eggs, which they classified as me-
galoolithid, an egg type affiliated with sauropods. Using some computer-aided 3-D
