Geoscience Reference
In-Depth Information
between fractures caused by a hatchling coming out of its egg versus those inflic-
ted afterwards would be very challenging. Nonetheless, trace fossils of “hatching
windows” were interpreted in 2002, evident in Cretaceous eggs from Mongolia and
China.Moresuchtracescouldbereasonablyproposedforfossileggswithlocalized
and consistently sized hatchling-appropriate holes in them, especially if more than
one is seen in the same clutch of eggs within a nest structure.
Other trace fossils that might be preserved in eggs would be those from the
aforementioned egg predation, where another animal—whether a dinosaur, cro-
codilian,lizard,snake,mammal,orinsect(dependingonwheningeologictimethis
might have happened)—nibbled, gnawed, bit into, or chomped an egg. Yet these
trace fossils have not been discovered yet either, despite many decades of our de-
monizing mammals for eating too many dinosaur eggs toward the end of the Meso-
zoic Era.
We also currently do not know whether dinosaurs laid unfertilized eggs—like
chickens or some other birds—but we presume that if their eggs are found in a nest
structure, these were probably fertilized. The extra effort required to build a nest
represents an investment of time, resources, and energy and would have exposed
parent dinosaurs to predators by keeping them in the same place for a while, thus
making them predictable. Instincts that would have impelled parent dinosaurs to
make nests with every laying ofan unfertilized egg clutch would have been quickly
selected out of those lineages.
An adage I often tell my students when discussing extinction is: “If you want
to make a species go extinct, stop it from reproducing.” The huge success of dino-
saurs throughout nearly every land environment within much of the Mesozoic Era
atteststohowtheyreproducedjustfine,probablyaidedthroughthevastmajorityof
them making nests for their egg clutches at the right times and in the right places.
Starting a Dinosaur Family: Building Nests
Given that at least some, if not most, dinosaur mating successfully resulted in fer-
tilization, and a mother dinosaur started internally producing eggs soon afterwards,
