Monday, 16 September 2013

Dinosaurian Myths: Take 2

Last week, we introduced you to a few different dinosaur-related myths ("Brontosaurus, all dinos were big, and Triceratops is no more) that are particularly irksome in my opinion. This week, we're going to continue on this theme with three more common dinosaurian myths! Since last week was 1-3, this week will continue with 4-6.

4. All large, prehistoric reptiles were dinosaurs
This is one that I've touched on before at the very beginning of Mesozoic Mondays, when I explained, in detail, exactly what a dinosaur is, and for that matter, what isn't. Dinosaurs are a group of organisms united by a very specific suite of characters, not just a group of big, scaly creatures. In fact, all of those swimming, and flying things normally called dinosaurs in a kid's toy set or book are not even dinosaurs! The large, aquatic reptiles come from several distinct groups, not closely related to dinosaurs. These include ichthyosaurs, mosasaurs, plesiosaurs, pliosaurs, and many more. "What about those scaly flying creatures like a pterodactyl?" Nope, not dinosaurs either. These are pterosaurs, which are closely related to dinosaurs, but not actually in the Dinosauria. "Does that mean that not a single dinosaur swam or flew?" Absolutely not. Dinosaurs would have swam occasionally to get across water, and there is evidence some spent more time in the water than others. However, there are no fully aquatic dinos that evolved paddle-like limbs to swim around. These are just other prehistoric, and indeed Mesozoic reptiles. When it comes to flying, there are of course a whole suite of dinosaurs that flew: they are the dinos that evolved into birds, and in fact birds. "Ok fine, but what about those guys with the sails on their back that we always see in books? Those are dinosaurs, right?" you may be asking. And the answer is: nope, they lived even before the dinosaurs, and are ancestors to modern mammals. In fact, they are more closely related to you and I than to dinosaurs! So spread the word: not everything was a dino! 

5. Mammals outcompeted/were more fit than dinosaurs
This common myth comes in several different forms, but the general thought is that mammals were somehow more fit/better than dinosaurs  and therefore outcompeted them and that's why mammals survived and dinosaurs didn't. This is, of course, false on many different levels. First of all, while mammals were living at the same time as dinosaurs, they were substantially smaller (in general), and were not (also in general) capable of competing with dinosaurs for anything. Dinosaurs were widely successful, living in every ecological niche on land, while mammals were mainly filling the niche of small, scavenger-like creatures. When the meteor hit the Earth at the end of the Cretaceous, the wide scale environmental changes that ensued made it very hard on the dinosaurs, which in general required a large amount of food to survive. It was then that the mammals were able to truly expand into the niches left empty as the dinosaurs died, and then that mammals evolved into the diverse group they are today. While this myth is mainly false, there is a slight ring of truth to it in that mammals were better able to adapt to the changes once the meteor hit, than the larger dinosaurs. However, that does not mean that they were better in general, and they were not responsible for the demise of the dinos.

6. Stegosaurus (or other large dinosaurs) had a secondary brain in its hips.
Still, to this day, this boggles my mind whenever I hear it. In the 19th century, American palaeontologist Othniel Charles Marsh noticed that large dinosaurs often have big cavities in their hips. As this is associated with the area that the spinal cord passes through, he suggested that this cavity actually housed a second brain. Unfortunately, it's difficult to know exactly what this was for. Birds often do show a slight expansion of the spinal cord in this region to help regulate their limb movements, but this is hardly on the scale of a second brain. It's likely that this area actually housed something called a glycogen body, which is also seen in the hips of birds, and helps to store energy. 
Stegosaurus. Image by Nobu Tamura
I hope you enjoyed and learned a bit more about these common dinosaurian myths! If there's anything that you often wonder about in palaeontology, let me know, and I may discuss it in my next blog!

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