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Screaming dromaeosaur biplane killers of the air



I'm probably going to pop off a reply to Nature concerning the latest paper 
on aerial dromaeosaurs so I must limit what I say here, but below are 
assorted observations. 

Steve Czerkas was correct that the Johel dromaeosaurs have fully developed 
arm wings. At the same time it turns out they had fully developed leg wings 
too. 

As Boris Sorkin pointed out to me at SVP, the legs of Johel dromaeosaurs 
could sprawl laterally because the femoral heads are spherical rather than 
cylinderical (verified by my high resolution photos of the type 
Sinornithosaurus, can be seen in the original Nature paper), and because the 
sinornithosaur described in Nature April 2001 is spread eagled with the legs 
splayed out. (In addition to the multiple specimens with the leg feathers, 
this leg specialization verifies the presence of a wing on sinornithosaur 
legs). This is never true of Archaeopteryx which is always preserved on its 
side because it had a more dinosaurian cylinderical femoral head and 
therefore could not sprawl the legs, and did not need to since it lacked 
large leg wings. The later, secondarily flightless dromaeosaurs logically 
reverted back to the dinosaurian cylinderical femoral head and vertical only 
legs.  

Since the legs could sprawl and the primary feathers are lift producing 
strongly asymmetrical, sharp edged and therefore fully aerodynamic structures 
of the sort always used for flight purposes in modern birds, there is no 
doubt the leg arrays were true wings. The leg wings are as big as the arm 
wings, so the former were not extra tail surfaces for normal flight. There is 
no reason to think the legs were habitually held in an inverted V (the use of 
that configuration on the Predator drone is entirely due to a combination of 
low radar return stealth requirements and the presence of a pusher prop that 
has to be protected from ground contact, the civilian version of the drone 
has a more conventional Y tail). They may have also been used for display, 
but only in the secondary manner common to the wings of many flying birds. 

Warnings to artists etc. The foot feathers did not trail posteriorly as shown 
in the flight restoration since that would minimize the lift generated by 
asymmetrical primary feathers, which are always held subperpendicular to the 
airflow. What is odd is that the foot feathers are preserved swept proximally 
relative to the metatarsals in at least two specimens. This would facilitate 
walking on the ground, but makes it hard to see how the feathers could be 
used as an outer wing. I suspect the distal leg feather bases were mobile via 
dermal muscles - the attachment of these big primaries on the nonaerodynamic 
foot was clearly very different from that on the streamlined hand bones - so 
the feathers could be swung outward relative to the foot during flight. Since 
there is no doubt that the leg wings were not used for thrust generating 
flapping for assorted reasons will not go into here this would be viable.  
More specimens might help figure whether foot feather orientation was 
variable. The life restoration of the biplane dromaeosaurs with protflier 
type narrow inner arm and leg wings is incorrect, the inner wing feathers are 
as long, and the wings therefore as broad in chord, as in modern birds. This 
means that the sinornithosaurs were not protofliers with tandem biplanes like 
Langley's failed Aerodrome. Besides, tandem wings are inefficient for large 
fliers since the aft wing is the wake of the fore which is why few have been 
dumb enough to repeat it since that dolt Langley. A better model would be the 
Nikitin-Sevchenko IS-1 for those in the know:).  

In no way are the Johel sinornithosaurs (incl microraptors) mere gliders that 
retained the ancestoral dino-avian protoflight condition into the Cretaceous. 
Instead they fulfill the predictions I made in DA for post-Archaeopteryx (at 
least temporally and in terms of flight abilities, probably phylogentically 
too) advanced fliers -- except for the extra wings. (See lines 9-11 in para 2 
in column 2 on p 239 of DA). In absolutely no respect are the sinornithosaurs 
less well adapted for flight than Arch, and no evidence has been presented 
that shows they were. In many respects they are obviously much better adapted 
fliers. Indeed, the sinornithosaurs approached cunfuciusornids and basal 
pterosaurs in flight adaptations.  Basal dromaeosaurs were early powered 
fliers that either show what was going on after the Arch grade, and/or 
represent a sideline, they do not tell us what was going on before Arch 
flight grade and using them for this purpose is very misleading. 

Heilmann's and Burian's "proavis" (latter's based on former's) illustrations 
actually show only small leg feather fringes, as well developed body and 
proximal tail fringes, so they do not really match the biplane dromaeosaurs. 
Fact is no one really predicted these beasts, which look like if anything 
mythical griffons (is tempting to speculate that Johel fossils started the 
legend but have to idea of the history). That all basal dino-avian fliers 
show adaptations for arboreality demolish both the belief that dinosaurs 
could not be arboreal, and that dinosaurs learned to fly from the ground up. 
Dial's work is interesting lab research that may or may not have something to 
do with the origin of avian flight, but it is inferior to fossil data. In 
Attenborough's bird series it was shown that the weak flying kakako often 
semi-glides and flutters from one tree crown to the base on another tree and 
then dash back up to do it again. Perhaps Dial's flapping up the trunk birds 
can be worked into such an arboreal flight origin scenario - cannot remember 
if the kakako flapped its way upwards - but there is no actual evidence or 
reason that dino-avian flight had a strong terrestrial component to it. After 
all, it is widely agreed that bat-flight originated among climbers, while 
there is no clear example of ground animals evolving flight. 

In his commentary Prum correctly notes that those who favor dromaeosaurs as 
post-urvogels need to explain why the sickle claws developed leg wings that 
Archaeopteryx and other birds lack. Actually that is easy to do. What has 
never been really clear is why protobirds would develop leg wings and then 
lose them.  

To those few who still clinge to a nondinosaurian origin of birds, for your 
own sake and ours do not do as I predict in DA (p. 217-218) by separating 
dromaeosaurs from dinosaurs and joining them with birds in a separate clade 
just because well preserved feathers have finally been found on the 
dinosaurs. You folks have spent considerable effort until now trying to show 
why dromaeosaurs were not closely related in birds - I had a good chuckle at 
SVP when one of the Oregon State folks actually tried to argue that the 
dromaeosaur pelvis was adapted for a crocodilian respiratory complex when 
dromaeosaurs have the most bird-like thoraxic and pelvic complex found 
outside birds. Suddenly making dromaeosaurs nondinosaurian birds will only 
show a state of embarrasing desperation. It's a hopeless case. Birds are 
dinosaurs just as bats are mammals. 

As for many prodinosaur folk it is best to get out of the unsubstantiated rut 
of assuming that every bird-like dinosaur is basal to Archaeopteryx, and 
inherently an "intermediate" form that tells us how flight evolved. I'm not 
pleased that the discussion has focused on the obsolete intermediate 
postulate when these biwinged, pterosaur tailed dromaeosaurs are the best 
evidence yet against the obsolete contention that no avepod dinosaurs were 
also birds that achieved sophisticated flight, and in many cases lost it.  

G Paul