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However, probably the most important trace fossils that prompted paleontolo-
gistsandtherestoftheworldtochangetheirmindsaboutdinosaurparentalbehavi-
or are dinosaur nests. Although dinosaur eggs had been known since the mid-19th
century, actual nests—structures deliberately built by dinosaurs that held and pro-
tected their eggs, and were also used to raise dinosaur hatchlings into responsible
members of Mesozoic ecosystems—were not described until 1979, and definitive
examples remained unrecognized until the 1990s. Still relatively rare compared to
dinosaur tracks and some other trace fossils, these nests and what they contained
nonetheless propelled and supported the revolutionary idea that dinosaurs cared for
theiryoung,behavinglesslikelizardsandmorelikemoderncrocodiliansandbirds.
Also, now that paleontologists know what to look for, I have every confidence that
more dinosaur nests will be found in upcoming years, expanding our understanding
of this formerly enigmatic dimension on how dinosaur lives began.
Mom, Dad: Where Did Baby Dinosaurs Come From?
Beforetalkingaboutdinosaureggs,babies,andnests,adiscussionofthepotentially
weighty subject of dinosaur sex is warranted, if for no other reason than that these
behaviors were a necessary prelude to fertilization, but mostly because such banter
is also great fun. For example, whenever dinosaur sex comes up in conversation,
its mysteries are summarized succinctly by the question “How did they do it?” The
incredulity behind such a question might reflect the wonder inspired from a trip to
a zoo or on a safari, where if one was timely enough to witness elephants, giraf-
fes, and rhinoceroses in an amorous moment, it also provoked ideas on how other
big animals, like dinosaurs, mated. Alas, these couplings can never quite satisfy, no
matter how much we might like to watch. After all, the largest bipedal dinosaurs
(theropods)mayhavebeencloseto8tons,andthelargestquadrupedalones(sauro-
pods) were 4 to 5 times that weight, dwarfing the largest of mammals and birds we
have today. There simply are no modern equivalents for dinosaur mating.
So how did two-legged male and female dinosaurs manage to keep their re-
spective balances while mating? How did four-legged males pick their front feet up
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