Finding Evidence in the Eggs at Our Forensic Labs - Walking On Eggs - page 68

The embryos lived at a time in which titanosaurs were common,
especially in South America. As mentioned earlier, we had found
their skeletons weathering out of the rocky cliffs near Dona Dora's
puesto. The fact that titanosaurs lived around Auca Mahuevo at the
same time as the embryos, however, does not constitute adequate
evidence to conclude that the embryos were titanosaurs.
Our embryos had pencil-shaped teeth, but could we find unequiv-
ocal evidence in the bones and teeth of the embryos that linked
them exclusively to either titanosaurs or to diplodocids and
dicraeosaurids? Most experts believe that diplodocids and
dicraeosaurids died out long before the late Cretaceous, but there is
no consensus on this point. Central to this debate is a late Cretaceous
sauropod from Mongolia called Nemegtosaurus, whom some regard as
a titanosaur and others regard as a survivor of the diplodocid-
dicraeosaurid group that survived long after most of its relatives had
gone extinct. When the teeth of the upper and lower jaws met as
Nemegtosaurus chewed, the crowns of the teeth were abraded such
that nearly vertical wear surfaces formed, as in at least some
titanosaurs. Surprisingly, a few teeth of our embryos had similar wear
surfaces on their crowns. Even though the embryos could not have
been chewing food before they hatched, they were obviously grinding
their teeth in the same way they would have done when they ate after
they hatched. Perhaps they were just exercising their jaw muscles to
prepare for life in the world outside. Thus far, we had established that
the embryos, Nemegtosaurus, and pencil-like-toothed titanosaurs all
shared the same kind of dental wear surfaces. So if Nemegtosaurus
was a titanosaur, the dental evidence would suggest that the embryos
were titanosaurs. However, the only known fossil of Nemegtosaurus is
a skull, which is not enough of the skeleton to determine if Nemeg-
tosaurus belongs with the titanosaurs or with the diplodocids and
dicraeosaurids, because little is known about the shape of the bones
in a titanosaur skull. Unfortunately, therefore, we had no basis for
comparison. There was at least one late Cretaceous titanosaurid
roaming the ancient Gobi named Quesitosaurus, but no skull of this
animal has yet been found. So we do not know what its teeth looked
like or whether the whole skeleton of this creature was like that of
Nemegtosaurus. Thus, although we can say that the embryonic teeth
from Auca Mahuevo belonged to sauropods, it is not clear whether