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Re: Archaeopteryx and Parental Care



In a message dated 2/5/02 1:05:47 PM Pacific Standard Time, 
TiJaWi@agron.iastate.edu writes:

<< I can't think of a single
 cursorial model which posits a quadrupedal ancestor (maybe Nopcsa?), nor can
 I envision why a terrestrial proto-avian would want "bat-like membranes"
 (though the authors may be referring to incipient patagia to increase
 surface area).  >>

In BCF, dinosaurs start out as arboreal quadrupeds (prolacertiforms) that 
used both fore and hind limbs for climbing. In time, the forelimbs decoupled 
from the hind limbs in locomotion via leaping, with hind limbs powering the 
leaps and the extended forelimbs catching the animals at the end of the 
trajectory. During flight, the forelimbs and tail became the primary organs 
that stabilized trajectory and eventually converted it from a plummet to a 
glide (as feathers on tail and forelimbs lengthened). When these arboreal 
leapers and gliders were grounded, hind limbs alone carried them on the 
ground and back up into trees; climbing-gliding forelimbs were useless in 
terrestrial locomotion. Eventually wings developed to the point that they 
could be used to become airborne with running takeoffs. Animals that diverged 
as flightless ground-dwellers from this scenario would have been natural 
bipeds and their descendants are the usual dinosaurs. Other uses for 
forelimbs (brooding, signaling, etc.) would be secondary to flying.