Understanding the kinds of potions allowed by an animal's joints can help scientists more accurately characterize an extinct species' range of motion. Photo by Armita Manafzadeh/Brown University
May 23 (UPI) -- Pterosaurs are key figures in the story of the evolution of flight. But new research suggests the flying reptiles didn't take to the air like bats, as has been previously suggested.
"Most of the work that's being done right now to understand pterosaur flight relies on the assumption that their hips could get into a bat-like pose," Armita Manafzadeh, a doctoral student at Brown University, said in a news release. "We think future studies should take into account that this pose was likely impossible, which might change our perspective when we consider the evolution of flight in pterosaurs and dinosaurs."
Ligaments dictate a joint's range of motion, but soft tissues are rarely preserved by fossilization. How are paleontologists to determine the movements allowed by the joints of long extinct species?
Manafzadeh used quail to come up with an answer. Using a dead bird, Manafzadeh carved away at the muscle surrounding joints. She recorded X-ray videos as she manipulated the bird's joints, pausing to get detailed images of the positions in which the ligaments prevented further movement.
Next, Manafzadeh cut out the ligaments and repeated the process, contorting the bird's limbs into all sorts of positions, stopping only when bone touched bone or when further movement caused a bone to pop out of its socket.
Her experiment -- detailed in the journal Proceedings of the Royal Society B -- showed that 95 percent of the movements and positions achieved without ligaments were not possible with ligaments.
Next, Manafzadeh and her research partner, Kevin Padian of the University of California, Berkeley, had to figure out how a quail's hip joint compared to the hip joint of a pterosaur.
Because bat limbs look a lot like those of pterosaurs, paleontologists have assumed the wings of flying reptiles worked a lot like those of bats. Bats' wings are attached to their hind limbs, so splaying their back limps helps to achieve helpful aerodynamics.
Manafzadeh's analysis showed such a position would have been impossible for pterosaurs to achieve. While the quail model was able to achieve a bat-like position without ligaments, the bird's ligaments prevented its hind legs from being stretched so far apart. The ligament that prevents such a motion is found in a majority of birds and reptiles related to pterosaurs.
More important than discrediting a common assumption about the flying positions of pterosaurs, the new research offers a blueprint for more accurately characterizing the motions allowed by the joints of extinct species.
"What we've done is to provide a reliable way to quantify in 3D everything a joint can do," Manafzadeh said.