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Re: Alvarezsaur spurs (was Re: dino-lice)



Hi everyone,

I've been researching the whole alvarezsaurid arm issue and I have
summarized some of my findings on my blog:

http://web.me.com/jasonbrougham/Site/Blog/Entries/2011/4/28_The_Paradox_of_the_Alvarezsauroids.html

I want to let you all know that I posted some inaccurate impressions of
the size of alvarezsaur pectoral skeletal elements in my earlier posts.
This was an accident, as I was misled by the inaccurate scale bars in the
Patagonykus monograph (Fig. 12) and the figure in Mesozoic Birds that was
based on the Patagonykus figure. I've also found this week that estimating
size from scale bars produces very large errors. My apologies, my
estimates were wrong but offered in good faith.

Patagonykus definitely had arms long enough to excavate termite mounds,
and I am persuaded that it did so.

-Jason





>
> True. We all await a fossil with soft tissue preservation. And now that
> alvarezsaurids are known from Asia, Europe, S. America, and N. America, we
> just might get one.
>
>
>> On 20 April 2011 20:51, Jason Brougham <jaseb@amnh.org> wrote:
>>>
>>>
>>> Thanks, man.
>>>
>>> You can see my reconstructions of maniraptorans using their wings for
>>> temperature regulation at:
>>>
>>> www.jasonbrougham.com
>>>
>>> go to illustrations/ecological and reproductive reconstructions. I got
>>> the
>>> idea from Hopp and Orsen (2004).
>>>
>>>
>>>
>>
>> Good stuff! It's a pity ideas (like yours) that link forearm mechanics
>> (or any biomechanics) to display are really difficult to test. The
>> conditions for a successful display are a lot harder to constrain than
>> for successful locomotion. I mean, other than assuming
>> more/faster/more complex motion is somehow better, there doesn't seem
>> to be a lot to go on.
>>
>>>> On 20 April 2011 14:54, Jason Brougham <jaseb@amnh.org> wrote:
>>>>>
>>>>> My favorite interpretation of alvarezsaur pectoral limbs has always
>>>>> been
>>>>> that they supported fans of long feathers or ribbon- like keratinous
>>>>> straps (like ETFs in scansoriopterygids) for display. In figure 18 of
>>>>> the
>>>>> Patagonykus monograph (Novas, F. E. 1997. Anatomy of Patagonykus
>>>>> puertai
>>>>> (Theropoda, Avialae, Alvarezsauridae), from the Late Cretaceous of
>>>>> Patagonia. Journal of Vertebrate Paleontology 17(1); 137-166.) there
>>>>> appears to be a lateral groove on Ph I 1 of the right manus, and the
>>>>> groove is over 40mm long. This feature, possibly combined with the
>>>>> ulna,
>>>>> may have served well in anchoring follicles.
>>>>>
>>>>> One virtue of my hypothesis is that it explains why flapping
>>>>> musculature
>>>>> may have hypertropied while the hand was reduced in both size and
>>>>> function. The shorter arm should have been able to flap or even
>>>>> vibrate
>>>>> at
>>>>> much higher frequencies and with some force. I picture the feather
>>>>> fan
>>>>> trembling not unlike the rectrical fan of the peacock. Another virtue
>>>>> of
>>>>> this hypothesis is that it is consistent with archosaur biology in
>>>>> that
>>>>> birds have arrived at a diversity of bizarre morphological
>>>>> adaptations
>>>>> for
>>>>> display, while none that I know of have been highly modified for
>>>>> digging.
>>>>>
>>>>> The problems include that the arm morphology doesn't really suggest a
>>>>> way
>>>>> to fold such a fan for fast running, and that the hands are not
>>>>> clearly
>>>>> modified for strong feather attachment with lateral flanges. But it
>>>>> is
>>>>> possible that the follicles lay in a soft tissue "remigial bulb".
>>>>>
>>>>>
>>>> Hey - this sounds neat. Fits pretty with Ostrich wing retention
>>>> (mainly for display) as well. I've heard (lemme dig around see if I
>>>> can find a paper) that Ostriches also use their wings for temperature
>>>> control as well. Could extend to other taxa as well? I mean, If you
>>>> believe that most Coelurosaurs have 'wings' to some degree, then
>>>> display gives you a good reason for maintaining forelimbs even if
>>>> they're%2
>>
>
>
> Jason Brougham
> Senior Principal Preparator
> Department of Exhibition
> American Museum of Natural History
> 81st Street at Central Park West
> 212 496 3544
> jaseb@amnh.org
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org