their eggs than previously thought—a factor
that may have contributed to their demise.
Scientists at Florida State University came
to this conclusion after analyzing the teeth
of rare fossilized dinosaur embryos. Like
human teeth, reptile teeth are formed during
incubation from a liquid called dentin;
this calcified tissue builds up, adding a
new layer each day as the embryo develops.
“They’re kind of like tree rings,” lead
author Gregory Erickson tells CSMonitor
.com. “We could literally count them to see
how long each dinosaur had been developing.”
The researchers calculated that smaller
Protoceratops hatchlings took nearly three
months to develop, while the eggs of the
Hypacrosaurus, a duck-billed dinosaur that
grew to be about 30 feet long, incubated for
about six months. With such long incubations,
dinosaurs must have been very slow
reproducers—a trait that would hurt their
ability to rebuild their populations after
a comet or asteroid strike wiped many of
them out 65 million years ago. The discovery
may also help explain why birds, whose
eggs have significantly shorter incubation
times than dinosaurs’ did, survived the same
mass extinction event.
