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 Parts of a Feather
 Wing Evolution
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Wing Evolution

   Wings evolved over many, many millions of years.  Scientists have extensively studied the wings of modern-day birds and have identified many important anatomical details. Especially important are those not found on the "arms" of non-birds.  Major efforts have gone into finding early occurrences of such details in the fossil record, but unfortunately it is far from complete.  Wings generally have thin, hollow bones that do not fossilize well and it appears that few of the animals that had them died in environments suitable for fossilization.  The lack of fossils makes it difficult to establish the time that each feature first appeared.  The times listed below are documented, but do not reflect an even progression from one step of deveopment to the next.

Sinosauropteryx - 125 MYA
   An adapted scapula, or shoulder blade permitted a greater range of movement in the forelimb.  This results in arms.  Although many animals, such as horse and dogs, have this bone, their forelimbs remained legs.
Velociraptor - 85-80 MYA
   The semilunate carpal was a half-moon shaped bone in the wrist of dromaeosaurids that permitted them to swivel their wrists.  It was this flexibility that would eventually make flight possible
Unenlagia - 90 MYA
   The scapula evolved into a different shape.  This allowed this ostrich-size animal to have greater up and down mobility in its arms. It now appears that other dromaeosaurids were able to move their arms this way too.
Archaeopteryx - 150-148 MYA
   This was the earliest known bird.  It had a small sternum (breast bone) and a long tail, which would have given it a rapid flight stroke and limited its ability to maneuver.  Flying was probably limited to short hops. 
Eoalulavis - 125-130 MYA
   In this primitive bird, the thumb has developed into an important structure to support the alula, a tuft of feathers that provide flight controls: the ability to run and bank while flying.

 

Modern Birds - 65 MYA to present
   They have small, lightweight bones, large wing surfaces and short tails.  Large sternums (breast bones) allow for large flight muscles.  These permit them to be excellent flyers