Re: Paedomorphosis ( Re: BARYONYX' CLAWS )

["Matthew Troutman" <m_troutman@hotmail.com>]

Matt Troutman ( me ) :

>> Bats have muscles that reach down their entire belly and have 
>>capacity for increased oxygen intake. Bats have very strong >>muscles 
and  they need bracing like birds do ( their clavicles act >>like the 
strut-like coracoid ).  

<<Of course they do. Muscles they need; the point is that they don't 
>need< those uniquely avian pectoral muscles to fly. Bracing in 
pre-modern birds was provided in large part by the thick furcula, and 
the flight musculature in pre-modern birds (which isn't preserved in any 
specimen that I know of) could well have resembled that of bats in its 
overall architecture. Stiffening of the back was aided by the addition 
of hyposphene-hypantrum articulations between the vertebrae, a feature 
commonly found in theropods (including small ones) that probably arose 
in conjunction with the development of flight and was retained in the 
large, flightless forms for weight support. There are all kinds of ways 
to accomplish the structural changes needed for flight, most of which 
result in creatures that can fly to a greater or lesser extent.>>

     The anatomy of the muscles in basal birds was just an early version 
of that of the modern birds. We have lots of evidence for the 
development of the avian musculature. First evidence of this is the 
robust, posteriorly grooved furcula. This type of furcula would not 
permit the typical ornithurine "spring". In birds the furcula anchors 
the M. pectoralis, and the posteriorly grooved design would anchor an 
exceptionally strong M. pectoralis. The M. supracoracoideus didn't 
develop fully in avian evolution until the triosseal canal was formed, 
but we have evidence that it was at an advanced level at the 
Archaeopterx level. The biceps turbercle ( the acrocoracoid process ) 
migrated from its more ventral position to the high, dorsal position it 
is at in Archaeopteryx and other birds. This suggests that the M. 
supracoracoideus, or, at least the precursor of it, was considerably 
advanced. The acute angle of the scapulacoracoid is an anatomical 
innovation that descreases the distance that the dorsal elevators (about 
3-5 of them ) work. The single sternum suggests that the musculature 
centered on the sternum was exceptionally strong so the sternum had to 
fuse into a single unit. The deltoid crest was more advanced in 
Archaeopteryx than any dinosaurs. Stiffening of the dorsal series may be 
a flight adaptation, but it can be a climbing adaptation as well. There 
are lots of ways to accomplish the structural changes associated with 
flight, but no theropods show features that can be considered unique in 
this regard. 

MattTroutman

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com