Geoscience Reference
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suggests that the mother or father
Citipati
arranged the eggs after laying, with such
a pattern constituting a trace fossil in itself. When viewed from above, the skeleton
andeggspaintastrikingportrait.Thedinosaur'sarmsareheldwideinasemi-circle
around the eggs, evoking images of a protective mother or father that died in a last
vain effort to keep their unborn children from harm. Paleontologists have also doc-
umenteddirectassociationsofdinosaurparentsandeggs—someofwhichhaveem-
bryonic bones linking them with their parents—with another specimen of
Citipati
and several examples of
Oviraptor
.
Takeawayaparentdinosaur'sskeleton,though,anddiscerningadinosaurnest
becomes a little more challenging. For instance, a cluster of identical dinosaur eggs
is sometimes considered as indirect evidence of nests. However, unless these eggs
areinsideabowl-likestructure,showsomesortofpost-layingarrangement,orhave
remains of a parent dinosaur on top of the eggs, a collection of eggs may not be a
nest after all.
Thisdoubtiscastbecausetheeggsmayhavebeenmovedafterlaying.Asany-
one who has done an Easter-egg roll can attest, or had an egg fall from a kitchen
counter to the floor while trying to make an omelet, well-rounded eggs can move
easily from one place to another under the influence of gravity. In nature, eggs can
be rolled or floated by currents, then deposited in low-lying areas with other debris
that, to an untrained eye, might look like someone's idea of a nest. Indeed, the dis-
covery of a dinosaur egg—containing embryonic bones, no less—in Late Creta-
ceous shallow-marine deposits in Alabama shows that at least one dinosaur egg
was capable of floating a long way from land. As we learned previously, dinosaurs
mayhaveoccasionallyswum,butlikemodernbirdsorreptiles,werenotinclinedto
make underwater nests.
In order to better understand what constitutes a dinosaur nest as a trace fossil,
a good starting place is to look at the traces associated with modern vertebrates that
lay eggs and make nests, such as those of reptiles and birds. If talking just about
reptile nests, these can be summarized into two broad categories: ground nests and
