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Re: The birds vs. the pterosaurs



Hi all:

Just a couple of thoughts to compliment those of Tom Holtz.

Steve Doolittle said:
 
"[Regarding the extinction of the dinosaurs] It's like Bob Bakker says about
mass extinctions: It's always the larger animals that get hit. When the mass
extinction occurred in the late cretaceous, who died? Certainly not the
smaller dinousaurs. Not the turtles or the little mammals or the little birds."

Well, we know that turtles, mammals, and birds survived, but as Tom Holtz has pointed out, many of these groups were still affected by the extinction.  Bakker is fond of saying something to effect of: "The frogs made it through the extinction.  They are very environmentally sensitive, so why is that they survived okay?"  As far as I know, we have no taxa count of the number of frogs, turtles, etc. that were in existence before and after the end of the Cretaceous.  Therefore, we do not know how well or badly frogs, turtles, and little animals did: my bet is many frogs and turtles were wiped out, but the fossil record is too coarse for us to know exactly what happened.

Steve continues:

"Perhaps they went extinct later,long after the mass extinction occured, because they were aced out by the birds. Perhaps the birds made the old flying archosaurs obsolete.

"Which brings me to this question: If the dinosaurs evolved into birds, why
did they do that when that ecological niche was already filled by the
pterosaurs? Because they could do the flying thing better? Maybe the birds
filled a niche that the pterosaurs couldn't?
I see evolution as a way for organisms not only to merely survive and become
"better" organisms, but also as a way to fill needed roles in specific ecosystems. Maybe those are the same things."

We must be very careful here.  The Theory of Evolution simply says that there has been descent with modification from a common ancestor.  It says nothing about organisms "improving" over time.  As an example, while certain animal groups have become more complex over time, many parasitic organisms are simpler descendants of more complex life.  Many parasitic organisms have simpler digestive and circulatory systems than their ancestors.  Therefore, life does not have to evolve into "improved" or more complex forms.

Paleoecology is a difficult subject to assess, because our knowledge of paleoclimate, paleoenvironment, and the number of species interacting with each other is very limited.  It is very difficult to test whether birds and pterosaurs competed directly with each other, or whether birds were filling an econiche that pterosaurs could not.

Steve:

"So what the hell happened to the little pterosaurs? If they were being "phased out" by the dominance of the birds, why didn't they fill another niche? I mean, the dinosaurs did it."

Well, not always.  Animals cannot always just fill another econiche.  Many factors are at play in extinction, interspecific competition, and econiche partitioning.  Many dinosaurs went extinct as well -- look at prosauropods: they died out by Mid-Jurassic times, presumably because sauropods did their "job" better, but who knows?  Keep in mind, too, that the whole Ornithischian clade bit the dust at the K/T, and only the saurischians survived in the form of birds (at least as far as we know).

Maybe birds had different reproductive strategies than pterosaurs which, by chance, allowed them to survive the K/T event.  Maybe pterosaurs depended primarly on seafood, and when the inland seas began drying up in the Cretaceous, their numbers were decimated.  Maybe pterosaurs were more environmentally sensitive than birds.  Maybe, maybe, maybe.  Again, the point is, paleobiology is not a simple matter to assess.  This makes it difficult to construct testable hypotheses about dinosaur and pterosaur biology as well as a number of other things, including paleoclimate, etc.

Steve:

"Perhaps, like the corvids of today, the pterosaurs didn't change much physically over the years, but instead "chose evolutionarily" to "work on their brains", ie, they adapted mainly by getting smarter. ) By the mid cretaceous, I believe the pterosaurs were the smartest thing on the planet. You can correct me if I'm mistaken."

Interesting point, Steve, but smarts don't guarantee you immunity to extinction.  Look at elephants, whales, dolphins, and maybe even ourselves.  Lord knows we're decimating primates at an incredible rate.  Insects do just fine and are not the brainiest guys in the world (no offense to bug people everywhere).

What happened to the pterosaurs may be linked to various aspects of their paleobiology we can no longer assess.  However, perhaps clues lie in the construction of their skeletons, their functional morphology, etc.  There may be some ways to assess some aspects of pterosaur paleobiology from their bones, and perhaps in this way we might approach how pterosaur and bird flight differ, which might be more efficient doing what, etc.  This might at least shed light on functional differences between birds and pterosaurs, and perhaps allow us to better assess specific areas of pterosaur paleobiology.

Good luck with your search for the cause of the pterosaur extinction.

Matthew Bonnan

 



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