(CN) — From humble beginnings, the pterosaurs, the first flying vertebrates, evolved to grow as big as 650 pounds with wingspans the size of airplanes. A new study of fossil records shows their flight efficiency improved with changes in their body size.
To dispel some common misconceptions, pterosaurs were reptiles, not dinosaurs. The animals shared a common ancestor, but their lines split some 245 million years ago.
“You can think of them as cousins of the dinosaurs,” said Chris Venditti, an evolutionary biology professor at the University of Reading.
And though pterosaurs preceded birds in taking to the sky, birds are descendants of dinosaurs, not pterosaurs.
Venditti led a study that examined the fossil records of 75 pterosaur species and used modern-day models of bird flight to illustrate how pterosaurs became highly efficient flyers over their 150-million-year history, from 228 to 66 million years ago when they went extinct with dinosaurs.
Due to an absence of proto-pterosaur fossils, it’s unknown how flight first evolved in this group. But they had wings made of skin and muscle membranes.
The anatomy of pterosaur bones may explain the lack of fossils of their forebears. Their bones were “very fragile-even hollow like we see in birds,” Venditti said in an email.
According to paleontologists, the first pterosaurs were small with jaws full of teeth and long tails, flapping behind a wide membrane connecting their hind legs.
They evolved into species with a variety of body types, from the size of sparrows to Cessna airplanes.
“Fans of the movie ‘Jurassic World’ will have seen a dramatization of just how huge and lethal these creatures would have been. Their diet consisted mostly of other animals, from insects to smaller dinosaurs,” Venditti said in a statement.
Venditti and his team of researchers from three universities in England published their study Wednesday in the journal Nature.
Using fossils to gauge the body mass and wingspan of pterosaurs, the scientists determined how their flight changed over time by calculating how much metabolic energy they expended in the air and how they glided by calculating their “sinking rate.”
“A low sinking rate enables not only longer travel distances per glide, but also allows for climbing in updrafts in which the sinking rate must be lower than the rate at which air rises from the ground,” the study states.
The researchers say their study showed pterosaurs became twice as good at flying over their 150-million-year existence, meaning they “adapted their body shape and size to use 50% less energy when flying.”
Because all flight is governed by the laws of physics, the team said, they were able to use a new model of flight based on today's birds to measure pterosaurs’ flight efficiency.
"One of the few things that haven't changed over the last 300 million years are the laws of physics, so it has been great to use those laws to understand the evolution of flight in these amazing animals,” said professor Stuart Humphries, biophysicist and co-author from the University of Lincoln.
But not all pterosaurs liked to fly.
The study found a group called azhdarchoids were competent flyers but preferred to forage on the ground.
One variety of azhdarchoids, Quetzlcoatlus, had a long stiff neck and grew to the height of a giraffe with a wingspan of 39 to 49 feet.
According to the researchers, they have established a new method of studying evolution going beyond merely understanding how creatures functioned based on their anatomy.
“It's really exciting now to be able to calculate the operational efficiency of extinct animals, and then to compare them through their evolution to see how efficiency has changed. We don't just have to look at the fossils with amazement, but can really get to grips with what they tell us,” said co-author Mike Benton, a University of Bristol professor.
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