h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Lovely article. I come down on the warm-blooded side of the argument myself. I remember, when this controversy first surfaced, someone mentioned that the plates on the back of the stegosaurus might not have had a wholly defensive purpose. They had a rich blood supply and might have been used in the same fashion as a car radiator, collong the animal off. Is there any truth to this?

sorry that should have said 'cooling'...

From what I know some of the relatives to the Stegosaurus(I think one of them is called Hiajagosaurus) had a sort of horns on their back instead of plates. They seem to be much more useless for radiation, but more useful for defense. So it was probably used simply for defense, or the relatives would have had to invent some new way of getting rid of the heat. And I don´t think they could have so fast.

But in Jurassic Park they actually do mention this about temperature. When the baby raptor is hatched they mention that it has a body temperature of 37 C, warmblooded.

Didn't dimetrodon have a big sail-like radiator on its back?

What puzzles me regarding the idea that baby dinosaurs would have been hatched at 37 C is that this implies that the mechanism that you get in crocodiles for determining sex, i.e. what temperature the egg was incubated at, couldn't have worked. Since they must have been all the same temperature, they would have been all the same sex, unless the Y chromosome became more significant before the dinosaurs evolved.

I never understood why crocodiles have that mechanism, what sense does it make? And as far as I know there is no direct line between crocodiles and dinosaurs. More of a cousin relationshsip, so no reason why they should have the same system. The same for Dimitrodon, it wasn´t a dinosaur.

In the movie (and the book) the dinosaurs were all the same sex. The book makes more of a point of it than the movie, as I recall. There is a plot point that is lost in the movie where some missing sections of dinosaur DNA was filled with splices from a certain frog species, one which had the (unfortunate) ability to spontaneously change its sex in an environment that had no mates... as Goldblum said, 'nature will find a way'.

Birds (and therefore, I assume, dinosaurs) determine their sex with Z & W chromosomes. ZZ = Male, ZW = Female. Incidentally this is opposite to what is found in mammals (XY = Male, XX = Female).
Reptiles do it by temperature.

Dunno if this is of any relevance, just thought I'd let you know

What probably happens in reptiles is that the genes which determine sex are activated or deactivated by proteins coded for genes on the same pair of chromosomes (not XY or ZW). These genes are in turn activated by temperature. When these chromosomes diverged into the X and Y millions of years ago, the activator and deactivator genes didn't go with the sex genes onto the various chromosomes, so it became irrelevant at what temperature the egg was incubated.

Whether X and Y divergence is a prerequisite for warmbloodedness, or the latter enables divergence to occur is anybody's guess. But the dinosaurs must have had distinct sex chrmosomes, as opposed to the reptiles which don't.

Wow, you turn your back for five minutes and a whole discussion starts up.

I subscribe to the theory that the plates on Stegosaurus Laticeps were used principally for defence given that both Kentrosaurus and Tujiuangosaurus had spike-like devices instead of plates. They may have been used for display, probably sexual display, since they had an excelent blood supply and would likely have dramatically changed colour if sufficient blood was allowed to flow through them. It is very likely that the crest of Triceratops Horridus served a similar purpose since it would have been useless for defence.

As for the chromasomal arrangements it is likely we may never know. There is an interesting possibility, however. Much genetic material is conserved even when unnecessary in descendant populations, perhaps the geneticists can recreate a dinosaur by playing with the DNA of birds..........

As pointed out above, Dimetrodon was not a dinosaur, it was a thecodontid reptile. Its substantial fin may have been used as a method of advanced heat regulation in an ectotherm. Of course nobody really knows.

Cheers,

Cestus