Geoscience Reference
In-Depth Information
two separate episodes of nesting had been preserved. Few if any
eggshell fragments were found between the clusters, as we would have
expected if the eggs had sat out on the surface for more than one year
and the eggs had been broken through natural deterioration. Clearly,
the eggs had been buried by flood debris before such breakage could
occur. This lack of eggshell fragments also suggested that each layer of
eggs represented a single egg-laying episode rather than an accumu-
lation of nests that had been laid over several breeding seasons. At least
several mothers had laid their eggs at this spot during a relatively short
period.
The mapping at the quarry helped to answer another question
involving parental care. We noticed that the eggs were generally
complete and, therefore, unhatched, and as already noted, we
observed relatively few fragments of eggshell between the egg clutches.
All this suggested that the females did not remain at the site after they
laid the eggs, because if they had, we would expect to find many more
broken eggs and eggshell fragments as a result of trampling. As pre-
viously mentioned, strong evidence suggests that dinosaurs more
closely related to birds, such as
Oviraptor
and
Troodon,
brooded their
eggs in much the same way that birds do today. Some ornithischian
dinosaurs may also have exhibited sophisticated parental care. Jack
Horner and his colleagues from the Museum of the Rockies in Boze-
man have suggested that hatchlings of the duckbill dinosaur
Maiasaura
were fed in their nest by their parents. Although evidence
for this is not as conclusive as it is for
Oviraptor
and
Troodon,
it is
believed that all dinosaurs offered some parental care to their broods.
Extinct dinosaurs belong to a genealogical group in which croco-
diles and birds are the only living members, which means that the
common ancestor of crocodiles and birds was also the common
ancestor of extinct dinosaurs. Despite their fearsome appearance
and predatory habits, crocodiles are exceptionally tender parents.
After carefully burying her eggs in a sandy mound of vegetation, the
mother guards the nest from intruders for about three months while
the eggs incubate before hatching. When she hears the chirps of the
babies emerging from the eggs, she delicately uncovers them, gently
scoops them up in her mouth, and carries them to the closest pond or
body of water. Birds have evolved a number of more intricate behav-
iors in parental care. Almost all of them incubate and protect the eggs
