Dinosaurs Quadrupedal

Well, the time has come to talk about dinosaurs. In a blog about evolution, it was inevitable. Dinosaurs are, so to speak, the elephant in the room.

It is widely believed that dinosaurs are big and go “Rawr!’. While it is certainly true that dinosaurs go “Rawr!” (of course, there’s a Santa Claus, boys and girls!), it happens that many were not very large.

Some were, of course, brain-meltingly huge. But others were the size of a chicken. In fact dinosaurs came in such a diversity of sizes and shapes, that talking about dinosaurs is a bit like talking about mammals: there are just too many of them to be able to generalize much. Mammals can be giant like an elephant – or a whale – or they can be tiny like a shrew. And they’ve changed dramatically over evolutionary time. Same thing with dinos: the first dinosaurs were quite different from the ones that got smacked down by that asteroid at the end of their reign.

But there’s one thing that seems to have remained the same over the entire age of the dinosaurs: the carnivorous ones always had a bipedal stance. From Allosaurus to Velociraptor, they all seem to have run on two beautifully engineered legs. Herbivores came in a surprising array of shapes both two-legged and four; but carnivores? Just the two-legged variety.

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Jumping the Evolutionary Assembly Line

Evolutionary biologists are like puzzle-solvers. That’s true for any of the sciences, of course, but there’s one kind of puzzle that evolutionary biologists particularly like to solve: the order of assembly puzzle. Here’s how this puzzle works. Take a complex system that works very well. Now, break it down into its component parts and figure out how they work together (sometimes, this step is done by the physiologist in the next lab over).  Finally, figure out the order in which the parts were originally assembled. But there’s a catch: every time you add a part, the system has to form a working whole. It doesn’t have to have the same function as the finished system, but it does have to be a working system. You can’t break an old system until you have a new system in place. Continue reading