A few weeks ago,Â in a post titledÂ The Curious Case of the Four-Winged Dinosaur, we discussedÂ the two theories for the origin of vertebrate flight.Â For some time, scholarsÂ have beenÂ divided into two camps as to how biological flight started. One side favors a ground up approach, known as theÂ Cursorial Theory,Â where dinosaurs, alreadyÂ feathered to preserve body heat,Â used the feathersÂ to help them run andÂ hop after fast-moving prey or from fast-moving predators, and eventuallyÂ evolvedÂ wings thatÂ were strong enough to get them off the ground and keep them airborne. The other side favors a top downÂ approach, known asÂ the Arboreal TheoryÂ where species started to glide between trees to escape predators or to attack prey.
The case in question dealt mainly withÂ Microraptor gui, a four-winged dinosaur excavated from the rich fossil beds of Liaoning Province in northeastern China, andÂ dated at between 128 to 124 million years old (Early Cretaceous). Microraptor was found to have glided, which one might contend supports the Arboreal Theory of flight.
Now, in a related story (sent in by a few of you),Â a new study claims that the ancient winged reptiles known as pterosaurs used a “pole-vaulting” action to take to the air.
According to a re-assessment of pterosaur fossils by Dr Mark Witton at Portsmouth University in theÂ UK and Dr Michael Habib of Chatham University in Pennsylvania, the reptiles apparently vaulted over their wings, pushing off first with their hind limbs and then used their powerful arm muscles to thrust themselves upward to take flight,Â notÂ unlike some modern bats.
Says Dr Habib:
“Instead of taking off with their legs alone, like birds, pterosaurs probably took off using all four of their limbs. By using their arms as the main engines for launching instead of their legs, they use the flight muscles – the strongest in their bodies – to take off and that gives them potential to launch much greater weight into the air.Â When they were far enough off the ground, they could start flapping their wings before finding a thermal or another area of uplift to gain some altitude and glide off to wherever they wanted to go.”
It’sÂ important toÂ noteÂ that, while not technically dinosaurs,Â Pterosaurs lived at the same time as the dinosaurs, including Microraptor. And thoughÂ they belonged to a different group of reptiles, the biological mechanisms for flying/gliding were similar across reptile species.
The study challengesÂ previous claims that the giant pterosaurs, such as Pteranodon, were too heavy and therefore incapable of flight. The largest pterosaursÂ were thought toÂ have had wingspans up to 13m and weighed up to 544kg. But the reappraisal of the pterosaur fossils suggests these numbers may have been overestimated.Â It now appearsÂ that the biggest creatures may have had 10-11m wingspans and weighed between 200 and 250 kg. And Witton and Habib maintain that the pole-vaulting action could have worked even for animals of that size.
We still don’tÂ know the origin of vertebrate flight, and the arguments between Arboreal and Cursorial supporters will rage on until more evidence is gathered. But cases like this, if accurate,Â where not necessarily addressing the flight origin, nevertheless demonstrate one step in the evolutionary process that falls obviously within the Cursorial Theory line of thought. This is a fascinating for those of us interested in biological flight; especially since it draws a different conclusion than those dealing with Microraptor.
And the scientific beat goes on.