W is for Wings

Pteranodon longiceps, at the NY Museum of Natural History

The flying dinosaur is a tricky concept. If you search “flying dinosaur,” you get a hundred sites that refer to pterosaurs as flying dinosaurs. But they’re not dinosaurs; they’re not on the dinosaur clade (family tree). They don’t have the right kind of hips or the hole in their head (see Letter “A”). Maybe 10% of those internet sites put “flying dinosaur” in quotes to show they at least know something, although most don’t bother (including MSN, Youtube, LiveScience and so on). Just to be clear, pterosaurs were flying reptiles, but not dinosaurs. Now that we have that out of the way, they were also cool. Just look at the bones, the arms, the wings!!!!

Meanwhile, scientists talk about non-avian and avian dinosaurs. What’s that about? Some reputable sites say the non-avians meant cold-blooded, the big giant sauropods. Others label all dinosaurs non-avian except for the one line, Avialea, that produced the modern birds. To recap, flying reptilian pterosaurs were not dinosaurs. Birds are avian dinosaurs. I would argue that makes all other dinosaurs non-avian. And one specific type of non-avian dinosaur was so close to birds that it may be considered a missing link between the two bird and dinosaur branches.

Whether dinosaurs or avian or not, their flight is also the subject of the day. How did they fly–compared with modern fliers? And what was so unusual about archaeopteryx, the fossil with a feather? I want to acknowledge right up front that I was inspired in this post by the paleontologist guru professor of the Rediscovering the Age of Dinosaurs Great Course, Kristi Curry Rogers. She specifically compared pterosaurs–those wonderful flying giant reptiles–to birds and bats, so I am going to borrow and share several of her ideas here.

Variety of pterosaur types compared w/birds. Wikipedia.

The Pterrible Gliders

Pteron is Greek for wing, so pterosaurs were “winged lizards.” Pteranodons were “toothless” and winged, while pterodactyls were winged and “fingered.” That’s what the names mean. Like the dinosaurs, these flying lizards also came in many shapes and sizes, although many of the discovered skeletons were pretty big, larger than modern birds.

Don’t ever forget, though, this means fossils found of pterosaurs, bigger than birds. That could be because, like birds, the pterosaur bones were hollow. If there were small hollow-boned flying reptiles, maybe their fossils didn’t last? The record of dinosaurs is the record of what has been found. You could be sitting a thousand feet up from a treasure trove of tiny pterosaur bones and never know it.

Still, the ones that were found were much bigger than modern birds. Their wingspans were vast — Quetzlcoatlus, as I mentioned a few posts ago, had a 50-foot span, the size of a small aircraft. Generally, pterosaur wings were wider than they were tall, which means these animals were phenomenal gliders.

How Arms and Wings Work

It’s useful to think about flight in terms of anatomy. Here’s a beautiful comparative skeleton of human, bird, and bat arms (thank you. batcon.org.) The upper arm is the humerus and lower arm pieces are radius and ulna. Carpal is the bone that all the metacarpals and phalanages attach to.

Comparative anatomy from batcon.org.

In birds and bats, the humerus is much shorter than that of humans. All these animals have a similar radius and ulna. After that is where it gets interesting. In birds, the metacarpals–the bones in the back of your hand–are reduced from five to two. They’ve lost three of their “fingers” which are fused into a single little nub. The other two finger support the end of the the wing. The flight feathers of birds are suspended from all of these key bones, the lower arm bones as well as the finger bones.

The design of a bird’s wing is also thicker at the front and thinner at the back, like a plane’s wing. That creates their lift through differentiated air pressure, that thing that I don’t like to think about when I’m in a plane, since it means you’re flying on nothing but science. Also in birds, the wings attach with extra strong muscles to a pronounced breastbone, which allows them to flap and lift practically straight upward, with a flourish.

Bats, in comparison, have the radius and ulna, but their metacarpals and phalanages–their fingers–extend far outward and form their wings. A membrane attaches from the outside of these arms, all the way down to their tail. The configuration of the bat design is what paleontologists were thinking about when they mused over the pterosaur structure. But bats aren’t reptiles, no matter how they might resemble other flying reptiles.

This flying design is what’s called convergent evolution. That is, flight evolved as an adaptation for them, just as it evolved for avian dinosaurs (birds) and pterosaurs. They all fly, even though they aren’t really related. Think of flight, as unusual as it might seem, like any other adaptation: meat-eating, tough skins, or long necks. It helped some group of animals acquire food and survive. Humans only find it remarkable because we don’t have wings.

Comparative pterosaur arm bones, from oceansofkansas.

Pterosaurs also have the shortened humerus with a medium-sized radius and ulna. They attach to a relatively smaller breast bone than birds, with fewer places for muscle attachments. Then, they have a single, long metacarpal which ends in four phalanges (fingers). Three of those sit on a wing “knuckle,” but the fourth extends outward to hold the entire wing. Yep, the ring finger as we call it, held the wing. And, remember, 50 FOOT LONG WINGS. That’s some big finger!

This configuration is what made pterosaurs fantastic gliders. There is a question about how they got off the ground, but clearly once they were, they could last for a long time. As a result, most of them were thought to live near coastal regions and possibly ate fish. Still, if they dove into the water, it would be hard for them to lift back up again. If they grabbed fish, it was probably with their feet or beaks while they were skimming, and not through diving.

Pterosaurs may have lifted by using their “knuckles.” Youtube/Live Science.

They couldn’t lift like birds. In fact, some argue that pterosaurs used those three finger “hands” as part of their walking and flying mechanisms. As our friends at Live Science have modeled on Youtube, the pterosaur would walk forward, speeding up by pushing off its knuckles, then at speed, open the wings and lift with its feet. Running and gliding, they would leap into promising air currents, rather than bursting upward like a bird.

In fact, they look so much like our dinosaur Yi Qi, the dinosaur with the shortest name, it’s surprising that the latter didn’t fly. Some scientists think he might have, because of the potentially long wings. Other say Yi Qi soared between branches, but would have to climb to them first, using the claws on hands and feet.

Yi Qi also had membrane across the phalanages, like a bat. Wikipedia.

How to Spell Archae…Bird-o-Saur

We can’t talk about flying and dinosaurs without talking about THE flying dinosaur. This was the guy that started all the talk when his fossil skeleton was first discovered in a German limestone quarry (Solnhofen) in the 1860s. They found the bones of what they believed was a reptile, but they also found that curious impression. It was clearly a feather.

Flight feather of the archeopteryx, wikipedia.

Over time, more than a dozen sets of bones were discovered, all similar, all with birdlike characteristics, and some with feather impressions along their limbs. They named the genus archaeopteryx which means hard to spell, er, “ancient wing.”

Archaeopteryx was small for a reptile or large for a bird–the size of a raven, perhaps a foot and a half or so. As with other fliers, their bones were light but their upper arms supported wings. However, they had teeth, three fingers plus claws, and a long tail, all reptilian marker, not birds. Long tail, but feathers–a sort of “missing link.”

The size of a raven, archaeopteryx is seen as the link between dinosaurs and birds. Wikipedia.

The ArchaeRenaissance

It was John Ostrom, during that dinosaur renaissance, who brought archaeopteryx back into the limelight. When first discovered in the 1860s, some thought the small flier might have been the bird-reptile link, but other biologists of the day put birds on a branch of the tree that split off much earlier from reptiles. It was Ostrom who saw new fossil finds of reptiles with feathers and thought to re-examine the archaeopteryx legacy. He argued that feathered dinosaurs were still dinosaurs. A cascading set of logic then emerges from that idea. If chickens are close to T Rexes, then it changes both how we think about chickens and about T Rex.

Ostrom’s thoughts also extended to how they used those feathers. It had been long proposed that birds must have begun their flight as tree dwellers, who leapt downward and eventually improved their gliding. O. C. Marsh, one of the early influential American paleontologists, argued for this “trees down” hypothesis. Others, like Ostrom, proposed a “ground up” approach. These animals were good at running, being bipedal. Perhaps, over time, they would jump up to catch prey like insects. If they grew feathers and shorter tails—over time–they would be able to leap higher and higher. Eventually, they’d be flying for short spans. Again, not individual animals but a grandson or a great-great-granddaughter might be building the body parts for flight.

Some in the Archaeopteryx genus could be quite small. From Live Science.

Ultimately, not everything that swims is a fish, not everything with scales is a reptile, and not everything that flies is a bird. Some of the fliers had long hands and others just one long finger. Some jumped up, some glided, and some flew down. All of them had to be light-boned. One thing is for sure, though. Paleontologists are getting more and more clever about digging out these smashed little guys from their resting places in the deep underground.

A Berlin specimen from the 19th c., with tail feather & wing feathers outlined. Thoughtco.

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