Can We Tell Whether a Dinosaur Was Male or Female?

We can learn a lot from dinosaur fossils, but the sex of the animal in question is frequently a mystery. Learn why in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff, a production of iHeart Radio, Hey
brain Stuff Lauren Bogle bomb here. Sue is the largest,
most complete Tyrannosaurus Rex skeleton in the world. Sue is
an impressive specimen, standing more than thirteen feet that's four
meters tall and forty two ft or thirteen meters long.

(00:22):
Many dinosaur fossils have missing or broken bones, but Sue
is more than complete, so it was also often displayed
as a real skeleton, not a cast. The bones that
you can see are the real sixty seven million year
old deal. Paleontologist Sue Hendrickson discovered the dinosaur's bones in
South Dakota on August twelfth of nine. Since then, researchers

(00:45):
have figured out a lot about Sue's life. In spite
of breaking some ribs, Sue lived to a relatively old
age for a dinosaur, at least according to signs of
wear on the bones. A Researchers also estimate that the
dinosaur weighed about seven tons, which is around as much
as a male African elephant. But what scientists don't know
is whether Sue was male or female. With just about

(01:09):
all living animals that use sexual reproduction, it's pretty easy
to figure out which sex is which, all you have
to do is observe their behavior or take a look
at their sex organs. Figuring out the sex of a
dinosaur is a little trickier though there aren't any around today,
so you can't observe their behavior, and since sex organs
are made of soft tissue, they don't fossilize well. On

(01:32):
top of that, most paleontologists believe that dinosaurs, like birds,
used one opening called a cloaca for both reproduction and
expulsion of liquid and solid waste, so even if researchers
find a dinosaur fossil with well preserved skin, they still
may not know it's sex for sure. DNA master reference

(01:52):
for figuring out what's what isn't much help with dinosaurs either.
While you can usually tell male and female mammals apart
by their X and Y chromosomes, reptiles don't follow those rules.
In many reptilian species, the temperature of the egg, not
the chromosomes inside it, determines the sex. Plus DNA breaks
down during fossilization, leaving little for researchers to analyze. But

(02:18):
that doesn't mean figuring out the sex of a dinosaur
fossil is impossible. Every once in an extremely long while,
researchers might find a skeleton with eggs inside it a
pretty good clue that one was female. One such find
cropped up in China in two thousand five, but eggs
aren't always the best indicator. It might seem likely that

(02:38):
a skeleton perched to top a nest of eggs belonged
to a female, but it's just as likely that male
dinosaurs like male EMUs and ostriches were the ones that
did the brooding. Another potential way of dividing males from
females is through studying sexual dimorphism. To think of male
peacocks that display huge ornate tails to attempt to impress

(03:00):
relatively nondescript female p hens. It could be that differences
in neck frills and head crests had to do with
the dinosaurs need to attract a mate. The size and
proportion of a dinosaur's body may have been sex related
to Paleobiologist Phil Center hypothesizes that the ultralong necks of
animals like a patosaurus may have evolved through sexual selection,

(03:23):
with longer necked dinosaurs attracting more or better mates. The
only trouble with this theory is that even if there
are sex differences in dinosaurs, we still don't know which
sexes which. Did a female triceratops use its neck frill
to attract a mate or was it the other way around,
where horns and tail spikes for defense against predators or

(03:43):
for combat with rival males. Without preserved samples of sex
organs or a time traveling look at dinosaur behavior, it's
impossible to say. Aside from the serendipitous find of a
dinosaur fossil filled with eggs or researchers have found and
one way to figure out if a dinosaur is female,
at least if she was pregnant at the time of

(04:04):
her death. In two thousand five, in the journal Science,
a team of researchers reported the discovery of what's called
medillary or medillary bone and a Tyrannosaurs rex fossil. In
birds which have hollow bones, medillary bone lines the interior
cavity of females bones. Birds use this type of bone
as a reservoir for the calcium they need to produce eggshells.

(04:28):
In all likelihood, the t rex whose bones the team
was studying was both female and pregnant. Unfortunately, Researchers can
only determine the sex of dinosaurs this way by breaking
into the interior of the bone. On top of that,
it only works that the dinosaur was pregnant when she died.
With groundbreaking discoveries like this and well preserved fossils still

(04:50):
being unearthed, it may one day be possible to make
a pretty good guess about a dinosaurs sex, but for
right now, it's a shot in the darkness m Today's
episode was written by Tracy V. Wilson and produced by
Tyler Clang. For more on this and lots of other
curious topics, visit how stuff works dot com. Brain Stuff

(05:13):
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