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RE: Oryctos Is Back




Mickey Mortimer wrote:


> It'd be great if these MANIACs who deny a theropod ancestry for maniraptorans 
> actually knew theropod> anatomy. Of the supposedly avian characters he lists 
> in archaeopterygid hands which are supposedly not 
> found in theropods...


This issue of _Oryctos_ is stacked with BANDit/MANIAC boilerplate.  Larry 
Martin's abstract says it all...


"The discovery of a primitive bird-like dromaeosaur (Microraptor) with four 
functional wings vindicates Beebe’s suggestion that birds went through a 
tetrapteryx stage in the origin of flight. Flight originated from an arboreal 
gliding ancestor and Longisquama may be more central to understanding how this 
came about than previously supposed."


You could write a whole paper just refuting that paragraph alone.  In fact, a 
plethora of papers have already done so.  To whit: 

(a) there is no evidence that _Microraptor_ actually adopted Beebe's 
'tetrapteryx' pose, since this required the femora to be laterally splayed; 

(b) even if it did, this does not prove that birds had an ancestry from among 
arboreal gliders, because we cannot assume that microraptoran behaviors were 
primitive for birds; 

(c) if birds did have an ancestry from among arboreal gliders then it doesn't 
rule out a theropod/dinosaurian origin of birds; 

(d) _Longisquama_ has absolutely nothing to do with the origin of birds (or of 
bird flight).  This last point has been thrashed out again and again and again, 
but it keeps on re-surfacing.


> - Deinonychus has reduced hyperextension in digits II and III, but plenty of 
> flexion (Gishlick, 2002). 
> Archaeopteryx seems to as well, especially in digit III and between II-1 and 
> II-2 (Paul, 2002). Paul 
> further notes confuciusornithids retain flexible digit III, though digit II 
> is less flexible in them and 
> microraptorians. Reduced hyperextension was probably present in 
> therizinosaurs (Falcarius lacks 
> extensor pits, for instance) and ornithomimosaurs (Gallimimus- Osmolska et 
> al., 1972) as well.


Yep.  Hyperextension of the manual digits has been tied to the ability of the 
fingers to act as 'shock absorbers' when grasping and holding prey.  The 
fingers could extend above the plane of the manus, to help resist violent 
movements of struggling prey (Senter and Robins, 2005).  It's no surprise that 
hyperextension was reduced in non-predatory theropods (like therizinosaurs and 
ornithomimosaurs), or in predatory theropods that grasped prey with both hands 
(like _Deinonychus_).  So there's no reason to assume that reduced manual 
hyperextension is an "avian" flight-related character.


Cheers

Tim
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