Just a minor rant…
I notice in animated protobirds and dromaeosaurids that they keep the arms nearly motionless while running (here), even though feathered (Fig. 1). Basically only the legs are providing thrust. The wings are only providing drag via decoration.
Figure 2. Click to see video. Microraptor gliding without so much as even a little flapping. What is it waiting for??
Same goes for animated climbing and gliding, like this animation of Microraptor. Very little to no flapping is shown in some sort of attempt at showing a primitive form of flying = weak gliding. What would happen if these hot little dinosaurs did a little flapping? Or a lot of frantic flapping whether on the ground or in the air? So what if they don’t have big sterna!
Start with a behavior, the skeleton will follow.
At this point we all are thinking about WAIR (wing-assisted incline running) discovered by Kenneth Dial (2003). All you have to do is take away the incline. Keep those birdy’s flapping!
And you don’t even need a wing to start with
Earlier we noted that, like birds, protopterosaurs (like Cosesaurus, Fig. 3) also developed a stem-like, locked-down coracoid which enabled flapping and discouraged traditional quadrupedal locomotion. And Cosesaurus was a long way off from developing wings and flying. However, starting with this odd secondary sexual behavior bigger, thrust and lift producing forelimbs came quickly in pterosaurs and Longisquama once flapping commenced in earnest.
So why don’t dino animators add a little thrust
to their running protobirds by adding a little frantic flapping of the forelimbs? After all, that’s how many (not all!) flying birds run (think chickens, sparrows and robins). And flapping wings still develop lift. So there’s no trade-off.
Well, modern bipedal lizards don’t flap. But then they all have a traditional coracoid and no arm frills. Many modern running birds, like the roadrunner and ostrich, don’t flap while they run. But chickens, ducks and songbirds do. So, the analog only goes so far.
What can the WWII Supermarine Spitfire tell us about thrust?
From Wikipedia: “In1938 the Spitfire was flown for the first time with ejector exhausts, developed for the Merlin by Rolls-Royce. With these it was found that the exhaust [gase]s [produced] 70 pounds of thrust, equivalent to about 70 hp at 300 mph.”
Even a little added thrust = added horsepower and added speed. And flapping had to start somewhere. Why not when feathers and a locked-down coracoid showed up? Start with a little, then move up to a lot. That’s the way evolution works.
Dial KP 2003. Wing-Assisted Incline Running and the Evolution of Flight (abstract). Science 299 (5605): 402–404. Bibcode:2003Sci…299..402D.doi:10.1126/science.1078237. PMID 12532020.