[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

FLIGHTLESS BIRDS



<<A running theropod evolving flight should have a tail no shorter and a 
sternum no longer than Archaeopteryx, lack ossified sternal ribs, have 
arms longer than other theropods, aerodynamically asymmetrical arm 
feathers, and be an insectivore.>>

Can you give us some reasons for this?  I am as skeptical of the 
'ground-up' notion as you are, but I see no reason for some of these 
features.  If anything a running protobird such have a shorter tail than 
Archaeopteryx to reduce drag; a longer, larger sternum for the 
attachment of large pectoralis and supracoracoideus muscles; and I see 
no reason why it should lack sternal ribs, which are one of the things 
that help raise and lower the sternum for lung ventilation (can you 
illuminate me?). Speaking logically, these features make no sense.  I do 
think that the 'ground-up' idea is nearly impossible to achieve, but 
these features make little to no sense.  

<<Secondarily flightless birds have very short tails, large sterna with 
ossified ribs, short arms, nonaerodynamic symmetrical arm feathers, and 
are often small headed herbivores that use stones to help grind food.>>

Whoa, whoa, whoa, whoa, whoa.  Where are you getting your avian anatomy?  
It is true that some flightless birds like the moa have completely lost 
the pygostyle, though some flightless birds have proportionally long 
tails (like alvarezsaurs and  _Struthio_).  Proportionally, all 
flightless birds have a reduced sternum.  According to somebody I can't 
tell you who he is (pers.comm), flightless birds, including _Apteryx_, 
have a sternum 25% of the length of the thoracic cavity.  I indepentedly 
confirm this and should note that volant birds have a sternum at the 
very least 50% of the thoracic cavity.  This nonsense about ossified 
sternal ribs being only present in flightless birds is false.  All birds 
have sternal ribs that are ossified.  Your latter points are true except 
for the last; flightless birds actually have fairly large heads, not as 
large as toucans or hornbills, but are still relatively large.  

<<The short, broad sternum with an anterior indentation is a dead
ringer for that of Archaeopteryx>>

A sternum of this form is seen in most early birds primitively.  
Enantiornithines have a proportionally larger sternum, but they still 
have anterior indentions for the coracoids.  

Look at more birds. :-) 

Matt Troutman

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