JJ2F tree.   20 March 03


In the Permian, plate-plumed gliders evolve.  
These give rise to the line leading to archosaurs, but from various points 
along this line, other plumed gliders spring off eg the line leading to 
Longisquama.
Megalancosaurus & other drepanosaurs are highly specialised "butterfly bone 
gliders", springing off from the road to archosaurs some way beyond 
Longisquama. 

Many archosaurs descend from the "trees" and lose their plumes.

"Warm-bloodedness" evolves in archosaurs, perhaps only once to the point of
proper homeothermy.  Creatures with this feature will have developed some of
their plate-plumes into fur (and may have lost their true plate plumes). 
Probably after this point the protobirds/pterosaur split occurs.  Pterosaurs
commit to flight on stretched skin, protobirds retain excellent 
terrestriality but combine it with plume-borne gliding.

Plate-plumed gliding protobirds start the long line of spinning off
ground forms eg thecodonts, herrerasaurs, tetaneurians, ornitholestians, 
maniraptors, flightless moderns.

Possibly facilitated by warm bloodedness, certain of those protobirds
that retained plumes were able to use them on their arms.  All such 
arm-borne plumes were potentially preenable, allowing reversible tearing 
the potential to evolve, though preening with teeth is hard to imagine.

Arm-borne plumes would have dragged along the ground unless the creature 
were bipedal - but obligate bidepality requires strength and balance control
not afforded by the nerves and muscles of poikilotherms while torpid.

At some point, presumably in the late J since it would have given rise to a
gigantic evolutionary explosion, which we detect in the early K, powered
flight evolved.  At about this time special features not seen in the gliders
arose.  These include complications arising from the fact that the wings 
were now preferable as aerodynamic surfaces to the tail since they used 
aerofoils for lift whereas the tail gave mainly high-drag plate lift. (This
aspect arises not from forward thrust itself but from considerations 
closely related to it.)  The loss of the tail and the development of the 
wings and pectoral girdle encouraged further fore-aft trunk compaction for 
reasons of balance.

Better understanding of the development of flight and birds can be made by 
justifying crucial staging points in the functional development of flight, & 
identifying them in the fossil record.  Needless to say it is a serious 
error NOT to see the evolution of birds and flight as being inextricably 
intertwined.




[plumes for plate-gliding]
|
|    Relative postns within following group unstated but chelonians pre crocs:
|
|    ----tortoises/turtles
|    ----Longisquama
|    ----Megalancosaurus et al
|    ----crocs
|    ----etc
|
[hard eggs and air sac breathing pre-crocs - they reversed latter due to sub-aqua.]
|
[highly active tendencies]
|
[branched feathers; warming up nicely]
|
+----pterosaurs
|
some thecodonts
|
+---other thecodonts
|
|    ----Protoavis with its juv. Coelophys. legs, Megalanc. neck, 
|                  & feather bumps fits nicely somewhere here;
|                  a better missing link that Archaeopteryx.
|
+---various dinosaurs
|
+-+--Proceratosaurus  
| |                   Long hands evolve to support primitive 
| |                   but slightly less inefficient primaries.
| +--Ornitholestes    Long fingers that can only pull prey, now stimulate 
|                     toe-2 claw to evolve as a weapon
|
|     Long hands and toe-2 claws did not evolve for climbing, as their 
|     extreme rarity in other clawed climbing types strongly suggests. 
|
|  NB therizinos can occur anywhere after here & before the uncs, though
|     probably nearer the main stem rather than a specialised branch.
|     Their ovi (eg ilium) similarities are due to their short tails.
|     ...& they, like flightless droms, may be polyphyletic...only more so;
|    two probably incompatible egg forms for therizinos are known.
|    Jufeng jaw probably prosauropod.
|
[modern flight feathers;  powered flight]
|
[pubis starts to retreat]
|
|
Archaeopteryx, [shortening tail]
|  
|  (confs. & enants not nec. FROM Ax, maybe a little pre, but approx here.)
|  
|    ---Confuciusornis  [pygostyle I]
|  
|    ----enant birds  [pygostyle II] 
|
+---"A"  (This might be a good place for (some) therizinos)
|
[slashing toe progresses, arcto-ankle develops, the latter supporting the former.] 
|
[any top end metatarsal fusion lost]
|
+-----+
|     |
|    [flight lost]
|     |
|    Sinovenator    
|     |       
|     +---later troodonts   [arcto completed] [pubis forward again]
|     |
|    [slashing claw lost, possibly more than once]
|     |
|     +---tyrannos
|     +---ornithoms
|     +---sundry little runners (though some may come from "A" or "B")
|
+---"B"  (This might be a good place for (some) therizinos &/or Avimimus)
|
+---first uncinated flying creature [ie with bony uncinate rib processes.]
     |     
     |
     +---Sinornithosaurus
     |
     +---+
     |   |
     |  [shorter mt for bigger toe-2 claw obviates arcto ankle]
     |  [tail lengthens & stiffens further to store energy for toe-2]
     |   |
     |   +----"droms" a [flight lost] [arcto ankle progressively lost]
     |   |
     |   +----"droms" b [flight lost]
     |   |
     |   +--- "droms" c [flight lost] etc
     |   |
     |  Rahonavis
     |
    [pygostyle III development starts] [toe-2 claw lost, possibly > once]
     |
    [arcto ankle progressively lost]
     |
     +---[loss of flight] Caudipteryx, oviraptors [reversal of pygostyly III]
     |          
     +---[loss of arcto ankle]  modern birds [more extreme pygostyle III]
             horrendous parallelisms with advanced enants.