A surprising factor in the extinction of the dinosaurs may have been how long their eggs took to hatch – Business Insider


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Approximately 66 million years ago, a massive asteroid or comet
smashed into the Earth near what we now think of as the Yucatan
peninsula of Mexico. On the other side of the world, in India, at
a place called the Deccan Traps, a period of intense volcanic
eruption began — one that would last tens of thousands of years.

These catastrophic and powerful events are often considered the
primary causes of the mass extinction event at the end of the
Cretaceous period that wiped out most of the dinosaurs along with
75% of life on the globe.

But brand-new research reveals another factor that may have
played a role in ending the era of the most massive creatures to
ever walk the surface of the planet. It seems dinosaur eggs took
a particularly long time to hatch. That means that when they had
to compete for sparse resources in a post-extinction event world
with the more efficient amphibians, reptiles, birds, and mammals
that made it through that era into the next one, dinosaurs may
have lost out.

Compared to reptiles, birds lay few eggs, and they are
particularly large. This could hamper their competitiveness,
since it exposes them to destructive risks. But bird eggs hatch
about twice as fast as reptiles (their behavior keeps eggs warm
and stable), which researchers think helps enough survive to
hatch. Dinosaurs still exist in the form of birds — avian
dinosaurs — and so researchers thought that the eggs of the
non-avian varieties would still hatch at about the same fast rate
as bird eggs do. After all, from what we can tell, non-avian
dinosaur and bird eggs have similar structures and birds are the
only remaining dinosaurs for us to base these hypotheses on.

But the new study, published January 2 in the
journal Proceedings of the National Academy of Sciences
,
reports that dinosaur eggs took far longer to hatch. For one
species studied, researchers estimate that a comparable bird egg
would take between 40 and 82 days to hatch. The dinosaur egg, it
seems, would have incubated between 83 and 171 days before it was
ready, more like a reptile.

And that changes a lot of what we know about dinosaurs.


Protoceratops
AntoninJury/Wikimedia
Commons


It’s all about the teeth

The amount of time it takes for young to be born has a
significant impact on how a species lives. It can define mating
season, migratory behavior, and other characteristics.

Dinosaurs had large eggs and, in general, adults expended more
energy than comparably sized reptiles or amphibians, putting a
limit on their competitiveness.

By studying the growth of embryonic teeth in other species,
researchers have been able to determine how long it took for the
infants of those species to develop. So the team behind this
study, consisting of researchers from Florida State, the
University of Calgary, and the American Museum of Natural
History, decided to try to calculate embryonic tooth growth in
two dinosaur species, Hypacrosaurus stebingeri (a sort
of “duck-billed” dinosaur) and Protoceratops andrewsi (a
less-famous relative of the Triceratops).

The researchers saw that a certain measure that can be used to
calculate embryonic tooth development in both human and
crocodilian species exists in dinosaur species as well. So they
evaluated fossil teeth from the above species.

Their calculations showed that the Protoceratops egg
would have taken more than twice as long to incubate as a
comparable bird egg, and would have been just a bit quicker to
develop than a similar reptile. The Hypacrosaurus egg
would have incubated even longer, needing more time than a
similar reptile.

As the study authors write, this means that many hypotheses of
dinosaur behavior may need to be re-evaluated. It was thought
that perhaps these species made long migrations back and forth
from the Arctic between seasons, but long egg incubation periods
may have made this impossible. And while these new findings are
just based on evaluations of fossils from two species of
dinosaur, the authors say they think these long incubation
periods would most likely be found in all toothed dinosaurs —
though further research could always change that conclusion.

The other big effect this may have had is on the extinction of
these creatures. We already believe dinosaurs expended more
energy and needed more resources than reptiles or amphibians.
They took a long time to mature, unlike many mammals and birds.
When the resources of the world were devastated by a changed
climate after the asteroid struck and during the period of
volcanic activity, it became hard for any large species to
survive. Slow hatching rates would have been just another blow to
the non-avian dinosaurs. And that may help further explain why
none made it through that time.

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