Climate Change and the Epic End to Dinosaur Sex

Last week on the science blog, I talked about polar bears and how when everyone thinks about climate change they think about the poor *little* polar bear. They’re cute, they’re murderous and well, quite frankly they’re screwed. What is not to love about polar bears?

In terms of animals that have ruled the earth though, polar bears are pretty low on the list of the beloved compared to some of the even larger mega-fauna to wander these lands. That’s right, forget about the polar bear, let’s talk dinosaur.

People love dinosaurs. They love their size, their supposed ruthlessness and how they looked like giant chickens (they do, just admit it). Whenever people in movies travel way back in time, it’s always to the dinosaurs and whenever there is some ridiculous pun to be made – we tend to go dinosaur. How could a million natural history museums be wrong? People love dinosaurs.

As lovers of these “terrible lizards” (or “monster chickens”, as I like to call them), there have been many theories as to what wiped out these creatures. There is the asteroid theory, massive volcano eruptions theory, and even the mammal competition theory.

One idea that has been tossed around has to do with climate change, and not just that the climate changed and food disappeared and the dinosaurs were too chilly and starved to survive. Rather, how temperature influenced sex-determination.

Now, you heard me talk about this a few weeks ago with painted turtles and tuatara, whose sex-determination is based on egg incubation temperature. When painted turtle eggs are incubated over a certain temperature, more of the eggs end up female and there are more lady turtles everywhere. Same for the tuatara in New Zealand, but instead warm temperature equals more male babies.

So what about dinosaurs? Well, about 65.5 million years ago there was some sort of extreme event (think massive asteroid), which released a bunch of dust into the atmosphere, blocking the sun, reducing plant productivity and making the world a different place. What gets people all worked up is that non-avian dinosaurs (i.e. what you and I consider dinosaurs) did not make it past this event, while other animals did. So the question is why?

This is where temperature-dependent sex-determination comes in. Researchers have suggested that when this big earth-changing event happened, the climate changed and while many mammals were totally cool with it (pun intended), dinosaurs were not and ended up having loads of boy babies (1). Sorry gentlemen, when it comes to preserving a species, having lots of boy babies doesn’t really help.

As an avid reader of my blog though, you know that some animals with temperature-dependent sex-determination did survive through this era into the current age: i.e. the tuatara. Researchers have suggested that some animals were lucky to have other traits like ectothermy that allowed them to survive through this climatic event – turns out there are other tricks to species survival than just sex and reproduction (2).

The important thing to keep in mind with all of this dinosaur sex-determination discussion is that it is still considered *very* controversial. This means that you are welcome to debate it with your stoner cousin or write New York Times best-selling novels about it, but there is not enough information yet to be so bold as to testify in front of congress. In the meantime, I encourage you to wax philosophical over your own dinosaur theories, they can’t object, they’re about 65 million years too late.

Further Reading:
(1) Environmental versus genetic sex determination: a possible factor in dinosaur extinction?
(2) Unexpected resilience of species with temperature dependent sex determination at the Cretaceous–Palaeogene boundary.

Minda Berbeco has a PhD in Biology from Tufts University and is a science writer in the Bay area. For those of you who read this post and thought “Oh just like in Jurassic Park”, she says “Nooo!” In Jurassic Park, the use of frog DNA is what lead to the dinosaurs changing sex after birth. This is something that some frogs can do in response to population sex ratio and sometimes also pollution, but not typically from temperature. Also, um, Jurassic Park is a work of fiction, just so you know.


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