Quetzalcoatlus

There are two Quetzalcoatlus species, a large one named Q. lawsoni and a very large one named Q. northropi.

• Q. lawsoni had a wingspan of 4.5 to 5 meters (15 or 16 feet), and a body mass anywhere between 20 and 65 kg (44 to 143 pounds), depending on who made the estimation. (The thing is that azdarchids were so completely unlike any living animal that paleontologists have to do a lot of imaginative guessing when trying to come up with a body mass estimation.)

  A modern harpy eagle, Harpia harpyja, with a mass about half of the lower estimate for Q. lawsoni, and a wingspan also about half, can lift up to 18 kg (40 pounds).

• Q. northropi was much larger, with a wingspan of about 10 meters (33 feet) and a body mass anywhere between 70 and 200 kg (154 to 440 pounds), again depending on who made the estimation.

  There is no modern flying bird even remotely comparable in terms of body mass and wingspan.

  There is still some debate on whether Q. northropi flew or didn't fly, and, if it did fly, whether it was capable of powered flight or only of gliding, and, if it was capable of powered flight, whether it could sustain powered flight or used it only in short bursts.

  For comparison, a common-or-garden modern unpowered sailplane with a dry mass of 200 kg and a wingspan of 15 meters is perfectly capable of carrying a pilot and some ballast, and a moderately skilled pilot can fly reasonably long distances (hundreds of kilometers or miles) even in less than perfect weather.