Dinosaurs Stopped Evolving

Jason Ward

Sat Jul 26 16:20:13 -0700 2008

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Perhaps the mesh of animals and forces at play meant that the status quo was the best adapted and most likely to survive. Its got to imaginable that point is reachable in any system. Jason

Dinosaurs Stopped Evolving

Gartogg

Sun Jul 27 21:28:04 -0700 2008

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Alternatively, could it be that the punctuation of the equilibrium was too violent for evolution, so that genetic drift was occurring, but no phenotypical signs are seen?

Dinosaurs Stopped Evolving

Eric Howe

Sat Jul 26 16:25:21 -0700 2008

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Aren't the dinosaurs that kept evolving called birds now? And maybe the rest were stuck in local maxima (but not so local that they could get out of it) for evolving the dinosaur form.

Dinosaurs Stopped Evolving

asdfg

Sat Jul 26 19:33:46 -0700 2008

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I always thought the explanation for the extinction of dinos a little lacking. Why did the meteor kill off every single species of dinos, but some mammals survived, some reptiles survived, some amphibians, fish, cephalopods, etc, etc? I suppose birds could be considered evolved dinos. I just seems a little weird to me that not even one or two "classic" dinosaur species snuck through while so many other, older fauna did. Any paleontologists out there?

Dinosaurs Stopped Evolving

mcrbids

Sun Jul 27 11:34:50 -0700 2008

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I just seems a little weird to me that not even one or two "classic" dinosaur species snuck through while so many other, older fauna did.

You mean, like the crocodiles, alligators, lizards, and snakes? You are making the mistake of asking why none of the "classic" dinosaur species survived, when the definition of a "classic" dinosaur species is that (ahem!) they didn't survive!

Dinosaurs Stopped Evolving

asdfg

Sun Jul 27 11:40:46 -0700 2008

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I'm under the impression crocodiles, et al are lizards, and not dinosaurs. (I think that is correct, but I guess I could be wrong.)

That's why is seems strange some ancient lizard species did survive, but no dinos.

Dinosaurs Stopped Evolving

The_Barbarian

Mon Jul 28 12:24:06 -0700 2008

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Why did Triconodonts (mammal subgroup) and all non-neornithes (Hesperornithes, etc) die out at the end of the Cretaceous? It ranges from difficult to impossible to tell why one sub-group dies out or lives in mass extinctions. There is really nothing special about the extinction of non-avian dinosaurs compared to the extinction of any other group.

I suppose birds could be considered evolved dinos.

There is no suppose about it. In common use, "dinosaur"; is used to mean "non-avian dinosaur";. On the one hand, you have Jeholornis prima, a bird capable of strong flight, but with a tail even closer to a dromaeosaurids' tail than Archeopteryx. On the other hand you have Sinosauropteryx, which was first described as a bird, complete with simple down-like feathers, but they soon realized it was a (non-avian) dinosaur related to Compsognathus.

Then there is Rahonavis. Scientists can't decide whether to label it "ave" or "dromaeosaurid". For that matter, some farther-out theories suggest that dromaeosaurids and troodontids should perhaps be considered Aves.

As you go from Theropods (including Carnosaurs, like Allosaurus, and Coelurosaurs) to Coelurosaurs (some, perhaps even most, had feathers of some kind) (Tyrannosaurs, Raptors, Oviraptors, Compsognathids, Ornithomimids) to Maniraptora (Raptors, Ornithomimids, Troodontids, Aves), there is increasingly little difference between "bird" and "dinosaur".

I just seems a little weird to me that not even one or two "classic" dinosaur species snuck through while so many other, older fauna did. Any paleontologists out there?

Oldness has nothing to do with fitness. Non-avian dinos were not fit by definition (they didn't survive), but why they where not fit, while aves,crocodiles, and lizards were, is not clear. Don't forget the extinction of the flying reptiles and the marine mosasaurs and plesiosaurs, and many other groups at the same time. And remember that although birds and crocodiles didn't go extinct, individual species and genera of those groups may have.

Dinosaurs Stopped Evolving

The_Barbarian

Mon Jul 28 12:31:28 -0700 2008

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New studies and constructing a dinosaur supertree are showing that they -mostly- stopped evolving and just maintained a status point for around fifty million years,

I am not seeing anything in the article to suggest that dinos mostly stopped evolving. It sounds to me like they just were not diversifying as much as had previously been thought.

Dinosaurs Stopped Evolving

Simon

Tue Jul 29 15:55:18 -0700 2008

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I think it is probably just they didn't change form. I don't see how you can tell they didn't take advantage of snakes or flowering plants, they just didn't adapt their shape to exploit these. I'm guessing big herbivores didn't need to do much to take advantage of flowering plants except perhaps turn there head towards the shiny things slightly - hmm tasty.

Sharks are another story. Ancient sharks were recognisably sharks, possibly even 400 million years ago. Modern sharks (often) have bigger brains, better sense of smell, smoother skin, better teeth, Fortunately a lot of shark teeth and scales survive in the fossil record so we know quite a bit about the changes in teeth and skin. I'm guessing this isn't true for a lot of "dinosaurs", so it maybe that dinosaurs just got better at being the kind of dinosaurs they were, then the world changed and being that kind of a dinosaur wasn't so good an idea.