How Do Dragons Fly?

If the texts of the Technic History must elaborately explain how Ythrians can be heavy enough for intelligence yet nevertheless can fly, then surely we need some explanation of how the ten-meter-long Borthudian dragons on Alfzar can fly?

In the original text:

"Huge leathery wings bore them aloft..."

-"Honourable Enemies," p. 67.

In the revised text:

"The beasts were less heavy than they appeared, and glided more than they actually flew. Just the same, a high-energy metabolism kept such a mass aloft."

-"Honorable Enemies," p. 285.

Just the same... More explanation was necessary.

In the best tradition of speculative fiction, imagine that the original and revised texts describe alternative Technic History timelines. In the original version, Martians are natives of Mars. In the revised version, they are colonists from an extra-solar planet who have been incorporated first into the Solar Commonwealth, then into the Terran Empire. Someone sometime might list all the differences.