Science Questions

Did temperature altering sex ratios make the dinosaurs die out?

Sun, 15th Jul 2012

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Question

Carol Brom asked:

Chris,

 

If crocodiles only produce males or females according to the Earth's temperature, i.e. if high then it is only males (or the other way round?); and if low then only females (or the other way round?). Then maybe that is what happened to the dinosaurs, as the Earth warmed up or cooled down for an extended time period. So only one sex was born and they couldn't reproduce?

 

Carol Brom.

Answer

Diana -   Well yes, temperature certainly has been linked to the demise of the dinosaurs, but normally, people associate it with the destruction of food availability or that plants could no longer grow in colder conditions.  So what you're talking about is something called Temperature-dependent Sex Determination which happens in crocodiles and turtles as well. 

Normally, what happens is when eggs are incubated at lower temperatures, you tend to get more males.  When they're incubated at higher temperatures, you get more females, although there are some variations on this.  Now we know that TSD – temperature dependent sex determination – happened about 300 million years ago so that is when the dinosaurs were around so it’s possible that dinosaurs did this.  But birds, which are descendants of dinosaurs, determine their sex genetically.  It has nothing to do with temperature.  So at the moment, we can't really argue that dinosaurs did have this way of determining sex.  And the other counter argument is that crocodiles and turtles have survived the asteroid collision – obviously, the temperature didn’t affect their breeding and also, there's evidence that dinosaurs actually purposefully laid their eggs in geothermally warm places so they could actually control the temperature of their nests.

Chris -   A natural incubator.

Diana -   Exactly, that kind of thing.  So, the TSD hypothesis is an idea that could potentially be true, but I think at the moment, it seems quite unlikely.

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