Geoscience Reference
In-Depth Information
viding the developing embryos with excellent conditions for incuba-
tion. Inside the eggs, the embryos grew to about a foot in length.
Though their heads, even with their relatively large eyes, were only a
couple of inches long, numerous pencil-shaped teeth had already
erupted from their jaws before they hatched, and the unhatched
babies exercised their jaw muscles, which they would soon need for
feeding on vegetation. Their skin was reminiscent of their other rep-
tilian relatives that lived alongside them; scales covered their delicate
bodies and formed roselike and linear patterns.
However, the nesting season did not always proceed according to
plan. Occasionally, storms large enough to generate floods in the
shallow streams swept across the ancient plains and surrounding
regions. The water in the channels overflowed the stream banks, car-
rying suspended particles of silt and clay that were deposited like a
muddy blanket across the flood basin. On at least five occasions,
this muddy blanket was thick enough to bury the incubating eggs in
the nesting colony, killing the embryos inside and beginning the geo-
logic processes that led to their fossilization.
But most years, when floods did not ravage the colony, the embryos'
development inside the eggs proceeded uninterrupted, and many of
the embryos hatched to begin life no longer than a baby crocodile.
Over the next few decades, the survivors grew to be more than forty
feet in length and to weigh several tons, making them some of the
largest animals ever to walk on earth.
Floods were not the only hazard that threatened a sauropod's sur-
vival at Auca Mahuevo. At least two perilous types of predators lurked
on the plains adjacent to the nesting colony. The one that we know
more about was
Aucasaurus,
a twenty-foot-long relative of the fear-
some
Carnotaurus.
This gracile carnivore moved swiftly on its two
powerful hind legs. Although its arms were short and were probably
not formidable weapons, its jaws were studded with dozens of serrated
teeth for slashing flesh, and its hind feet were equipped with razor-
sharp claws for taking down prey. As if these attributes were not
menacing enough, its skull was adorned with small horns over the eyes.
Clearly, solitary adult aucasaurs were capable of preying on hatchlings
and juvenile sauropods that frequented the floodplain, and if the
aucasaurs joined together to hunt in packs, even adult sauropods could
have been in jeopardy.
