September 12, 2008
Dinosaur vs. Crocodile: Who Wins?
Turn the clock back 230 million years, and the land was covered with big, toothy reptiles.*** But as many a nine-year-old can tell you, not all of them were dinosaurs. Some were “crurotarsans,” a lineage that all but died out just as the dinosaurs were acheiving global domination. Today, the only crurotarsans are the crocodiles. But alas! It all could have been so different, according to research published in Science today by Stephen Brusatte, of Columbia University, and colleagues.
The Age of Dinosaurs may have been a matter of luck, they say: just a matter of which group was hit harder by a mass extinction 200 million years ago. Before then, for nearly 30 million years, dinosaurs and crurotarsans had vied for superiority in a classic Darwinian struggle.
And the crurotarsans should have won, the scientists argue. After analyzing the fossils of 64 species, they found the beasts had a greater variety of body plans – and evolved new species at about the same rate – as dinosaurs. They take this as evidence that dinosaurs weren’t innately superior creatures (otherwise, the reasoning goes, more dinosaur species would have evolved as they usurped the crurotarsans). In the race for supremacy, it wasn’t that the dinosaurs outpaced the crurotarsans – it’s more like the crurotarsans were felled in the home stretch by a calamity.
But hang on a second. I’m all for exciting new theories that offer explanations no one’s thought of before (i.e., prairie-stalking pterosaurs). But this logic sounds wonky in a few places. Does a lack of species divergence have to mean an ecological stalemate was going on? Or could it mean that the species in existence at that time were doing phenomenally well on their own? For that matter, might the rapid appearance of new species signal a sputtering lineage, dying out in a flash of ill-fated new forms?
More problematically, how does a mass extinction kill nearly all the members of one group (crurotarsans) without destroying a similar number of the other (dinosaurs)? That doesn’t sound like the luck of the draw; it sounds like one of those groups had a competitive advantage – what the regular person might call “superiority.”
Full disclosure: I’m not a paleontologist. Perhaps these are well-thought-through ideas that the authors lacked the room to explain in their paper. (If so, I’d love it if a real paleontologist would write in and educate me.) Maybe the authors imagine that a different kind of mass extinction (meteoric fireball vs. global warming, for instance) could easily have switched the tables and led to an Age of Crurotarsans.
But then, the crocodiles did survive, apparently content to hide out in the swamps for 200 million years while the dinosaurs enjoyed their 135 million years of fame – and then died out. Come to think of it, maybe the crurotarsans are superior after all.
(Image: the crocodile, last of the crurotarsans, Wikipedia)
***To be fair, there were also plenty of small and medium sized reptiles, some with rather ordinary teeth.
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Duh! Obviously the dinosaurs had the ability to survice the supposed meteor impact whereas the crurotarsans didn’t fare as well. THAT is called an evolutionary differentiator (what ever it was) NOT luck.
Comment by John — September 12, 2008 @ 1:30 pm
Nice finish-I like the idea that we may be still in the early stages of a growing Age of Crurotarsans! One note, though: it seems like it wouldn’t have mattered if it was a fireball or global warming that prompted the extinction of one versus the other; it would still be competitive superiority to one of a number of possible catastrophic selective pressures, reinforcing your earlier statement.
Comment by sitta — September 12, 2008 @ 1:48 pm
Hey sitta – you’re right in saying that, were any type of mass extinction to wipe out one group and not another, then that would be an example of competitive superiority rather than luck. I think the luck the researchers were referring to was in the pure cosmic luck of which type of mass extinction dropped out of the sky at that one moment in history, 200 million years ago. I agree with you, though, that calling such a lopsided extinction a matter of luck is rather overlooking the abilities of the creatures involved.
Comment by Hugh — September 14, 2008 @ 10:32 am
I wouldn’t say the dinosaurs’ survival was a matter of superiority, or “survival of the fittest” as people like to say. Instead, I would call it “selective advantage.” While the crurotarsans were competing quite well before the mass extinction, the world changed and somehow the dinosaurs were better able to survive the extinction event and its aftermath.
Exactly how did the world change at this time and what were the adaptations that tipped the balance in favor of the dinosaurs? These are the questions the paleontologists are posing about this and other extinction events. Of course, we don’t have all the facts available to us after all this time; and looking at the modern world — where you would think that we knew just about everything that is going on at present — biologists are struggling to determine the causes for patterns of extinction and survival happening under our very noses. So I suggest we cut the Triassic CSI team some slack. Their ability to solve these mysteries depends largely on the evidence available to them.
Regarding the extinction of the dinosaurs, let’s not forget that the birds — which are living dinosaurs — did survive the mass extinction event that took place 65 million years ago. Mammals certainly take the prize for the biggest animals alive today, but their diversity is only half that of the birds, which comprise some 10,000 species.
And there is no disputing that the feathered dinosaurs we call birds outnumber modern crocodilians big time. On the other hand, if you want to look at it from the perspective of brute strength, a large saltwater crocodile is a lot bigger and scarier than the biggest bird (the ostrich), though an ostrich is way faster and packs a powerful kick.
Comment by Dino Guy Ralph — September 14, 2008 @ 11:39 am
thanks
Comment by Keuts — September 15, 2008 @ 6:38 am
Hey DGR – thanks for weighing in on behalf of the paleontologists. I do often marvel at their ability to reconstruct details of worlds long past.
But while paleontologists deserve credit for piecing together details such as what animals looked like, what they ate, and how fast they ran, I do wonder if they’re being a bit rash when they write off the extinction of one whole lineage versus another as simple bad luck.
It’s easy to feel wistful for the crurotarsans, a marvelous and diverse lineage that died out, Mozart-like, before we got to see what they were capable of. But in the end, debating the superiority of dinosaurs over crurotarsans starts to sounds like a game of “If the Green Lantern and the Silver Surfer got in a fight, who would win?” We all have our favorites, but we’re never going to know. Maybe it’s better that way.
Comment by Hugh — September 18, 2008 @ 1:38 pm