Biology news 2: Male and female dinosaurs

The second in the series is an interesting one: now you can tell which dinosaurs are male and which are female. The story is here: http://www.sciencemag.org/cgi/content/abstract/308/5727/1456

So, how can you tell a girl dinosaur apart from a boy? If you had a whole dinosaur, it would be easier: you could look at reproductive organs, which ones laid eggs, who raises the kids, who wears lipstick, etc. But scientists don't have the luxury of observing whole, live dinosaurs. They don't even have whole, dead ones. All they have is fossilized bones!

So, we have to use something else to tell which one is male and which is female. The typical methods used relative size to tell if an animal was male, and it was usually not very reliable (so, that huge, scary T rex you saw at the museum might have been a mommy or a daddy!).

Now, scientists have found a Tyrannosaurus rex in the Rockies that they know for sure is a female. A fertile female. One who was laying eggs.

How do they know? Well, it turns out that when female dinosaurs are laying eggs, they change the inside of the bones in their back legs. The coolest thing about this is that birds do the same thing!

In current-day birds (especially ostriches and emus), when the girl birds start to make eggs, their hormones (like estrogen) go up, and they make this lining on the inside of their bones. The lining has calcium in it that helps them make eggshells. Amazingly, only birds do this.

So what does this mean? Well, for one it means that any dinosaur that has this special type of bone lining is definitely a female. It means the female was laying eggs.

And it also means something else: it means that dinosaurs are related to birds, especially ostriches and emus! So next time you see an ostrich at the zoo, remember: its great-great-great-great-great-great... grandmother could have been a T rex!

rani