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Re: Microraptor hanqingi, new species from China.



Jason Brougham <jaseb@amnh.org> wrote:

> Alright, fair enough, petrels are squatter than Archaeopteryx. But there are 
> bipedal, cursorial, theropods with the bauplan of long legs and long necks 
> and small, elevated, halluces that
>  are not fully capable of perching - and they also roost in trees. Galliforms 
> like turkeys, I'm thinking of.


Turkeys have a descended, reversed hallux that is eminently capable of
opposing the anterior toes.  It's just not as specialized for perching
as in those birds (including other galliforms, like cracids) that
spend much more of their time in trees.  The peacock is similar to the
turkey in this respect.


> I was worried that someone would say petrels can sit in trees because they 
> descended from birds that had functioning halluces. It seems illogical to say 
> that a morphological character
> is crucial for a certain function, but that the function can be retained even 
> if the character is lost.


That's not what I said at all.  What I said was that the morphology of
modern flighted birds is quite different to that of theropods like
_Archaeopteryx_ or _Microraptor_.


> Let's just take this moment to note, there are theropods with no halluces 
> that roost
> and nest in trees. If you don't believe it google image search "petrel tree".


I believe that petrels can roost in trees.  I also happen to think
that it's largely irrelevant to the ecologies of _Archaeopteryx_ or
_Microraptor_.


> I am troubled that you dismiss any comparison between the function of basal 
> paravians and modern birds because the former have long necks and legs.


Again, that's not actually what I said.  I was speaking to the overall
bauplan.  Paravians like _Archaeopteryx_ or _Microraptor_ were
cursors; the proportions and ranges of motion at the joints reflect
that.


> In reality, this fact is little
> appreciated, but Microraptor, Anchiornis and Xiaotingia have necks roughly as 
> long as their skulls, putting them closer to medium - length - necked birds 
> like crows than they are to
> long - necked forms like storks or ducks.


But not to petrels, which is what my statement was in response to.


> The former retain long bony tails, of course, but it's not clear that basal 
> paravians would have had important functional differences from
> phasianids like peacocks with much heavier and longer masses of feathers on 
> their tails. If turkeys and peacocks aren't close enough to basal paravians 
> for you to serve as analogs,
> then no animal alive on earth today is, so no analogs can be cited.


Turkeys and peacocks are poor analogs for basal paravians.


> There is no perfect analog alive today for basal paravians, but the imperfect 
> ones we have demonstrate that there is no inviolable rule. No one has 
> identified and measured a set of
> morphologies that correlate with the ability to roost in trees in living 
> animals, so this possibility cannot be excluded for basal paravians.


Fair enough.  But I'll turn this statement around and say this
possibility (roosting behavior in basal paravians) should not be
*assumed* until this work is done.  Simply saying "Well,
petrels/turkeys/tinamous roost in trees, why not _Archaeopteryx_ or
_Microraptor_?" is not a valid scientific argument.







Cheers

Tim