Were Pterosaurs too heavy to fly?

Pterosaurs, the flying dinosaurs who are believed to have ruled the sky millions of years ago, might actually not even been able to fly (at least not the biggest ones), as claimed by a study from Japanese scientist Katsufumi Sato.

The giant pterosaurs might not have been able to fly

How did Pterosaurs achieve flight?
Many adaptations on the creature body are thought to have allowed it to fly. Among them, their hollow bones and wing shape.

Too heavy to fly
Japanese scientist Katsufumi Sato conducted a research measuting the flight patterns of Albatross birds, finding their wingspan and body to weight ratio.

He concluded that the giant creatures were simply too heavy to takeoff; however, his research covers only avians with a wingspan of 5 meters at most, whereas big Pterosaurs such as the Quetzalcoatlus Northropi are known to have wingspans of 10 meters or more. Katsufumi Sato recognizes this, and unless they have a different way of flight than most birds, their ability to fly remains a subject of debate.

Modern dinosaurs
Pterosaurs are the only ancient creatures that didn't completely die off; we can see them today in the shape of birds.

From dinosaur to bird. In fact, birds are somewhat classified as reptiles as well (Source). Maybe the skies were not terrorized millions of times ago by flying monsters as we have always thought. What are your thoughts?
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