Thursday, April 30, 2009

Ruining the fantasies of kids everywhere: Study claims big Pterodactyls couldn't fly

One of the coolest dinosaurs you learn about as a kid are Pterodactyls (really Pterosaurs, but who's checking). As giant flying lizards, these guys are thought to have dominated the skies long before birds existed (from the late Triassic to the end of the Cretaceous, 220–65 million years ago). The biggest of the bunch are Pteranodon and Quetzalcoatlus, which are thought to have weighed as much as 250 kg with wingspans in excess of 30 feet.

But a new study, published in PLoS ONE is casting doubt on the ability of these massive winged dinos to actually fly. Instead, their results add to others which support these creatures as land animals who staked their prey, not swooping in to grab it.

In the study of flight, scientists generally believe that there is a "maximum size" that animals can be and still be able to fly. It has to do with competition between muscle power and power needed for flight. The heavier a creature is, the more force it must create with its wings to be able to lift that mass off the ground. However, muscles can only get so strong and bones can only resist so much force before breaking, causing there to be an maximum size limit, after which the animal is just unable to produce enough force. However, it's debatable exactly where this upper limit is because creatures use different wing shapes, sizes and flapping patters to achieve flight.

The extinct pterodactyls, though as big as a modern giraffe, have been compared in wing shape and presumed flight method to modern large birds like albatrosses, which are called procellariiforms. So researchers looked at how today's large birds are able to fly, and what kind of weight limits might exist for them.

To see how the birds flew, they attached little acceleration data loggers attached to the birds wings to chart the flapping movements. They compared these data to the bird's weight, wingspan and wing surface area to see whether there was a correlation between how the birds flew and how big and heavy they were. They also took physiological measurements of the birds exertion during these behaviors.

They found that the birds used two types of flapping to fly: a high-frequency one to get off the ground and a low frequency one once in flight to maintain altitude. As predicted, both high and low flapping frequencies decreased according to the size of the bird, suggesting that at a certain weight, they simply could not flap their wings fast enough to attain lift off or maintain flight in the absence of wind. The researchers calculated that this weight limit was around 41 kg, which is about 1/2 of what the average large, ancient pterodactyls are thought to have weighed.

"Our study of living Procellariiformes as model animals suggests that if pterosaurs larger than 41 kg (or 5.1-m [>15 foot] wingspan) had the narrow wings, they could not have attained sustainable flight in environments similar to the present," write the authors in their concluding paragraph. They go on to add that "the results of the present study lend support to a recent reappraisal suggesting that large pterosaurs were terrestrial stalkers, finding much of their food via terrestrial, ground-level foraging."

In other words, the study authors suggest that the great flying dinosaurs actually couldn't fly, at least not well enough to use it as their main hunting technique. Instead, the Pterodactyls were grounded. They do note, however, that their data don't completely rule out the possibility of flight. Other conditions could have been different in the past, including a lot more wind and thermal updrafts (like the ones which fuel vulture flight). Even the air itself could have been denser, or gravity slightly weaker. So the majestic image of huge, flying Pterodactyls isn't an impossibility.

None the less, the researchers do a pretty good job of destroying the fantasy dinosaur images of children everywhere by knocking the Pterodactyls out of the sky. Those flying monsters are the best part! And if they really didn't fly, well, dinosaurs just got a little less cool in my book.

Sato, K., Sakamoto, K., Watanuki, Y., Takahashi, A., Katsumata, N., Bost, C., & Weimerskirch, H. (2009). Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs PLoS ONE, 4 (4) DOI: 10.1371/journal.pone.0005400


Anonymous said...

I'll just hang onto those remote possiblities. Weaker gravity eh?

Anonymous said...

First off, weren't pterodactyls non-dinosaurs? Secondly, does this rule out the possibility of flight for *all* pterodactyls, or only the largest? There were many smaller species, after all.

LUCKY said...

I think they could fly. I've seen the flintstones but I also think Pluto is still a planet. However I don't know much about the hard sciences so take my thoughts with a grain of salt

Jane Shevtsov said...

Wasn't there more oxygen in the air during that period? That could fuel greater exertion.

But "weaker gravity"? LOL

WhySharksMatter said...

Of course they can fly. I've seen them do it on lots of movies. No know-it-all scientist is going to tell me otherwise. First Pluto, now this...

Bryan W/a 'y' said...

"A couple of things here that are of importance:

1. Pterosaurs are NOT dinosaurs. They are archosaurs yes, and probably closely related to dinosaurs, but lie outsie of Dinosauria.

2. There is a huge difference between 'not being able to fly' and 'not being able to thermal soar / dynamic soar' and these are not always well separated.

3. I can't think of a single pterosaur expert who things they have wings constructed like an albatross in temrs of the aspect ratio / chord. Pterosaurs are rather different animals in a great many ways, and the *structure* of their wings was clearly very different to that of birds. While it's true that we don't know much about how they did function, to assume that they are likely to be similar is a mistake.

4. Even the largest pterosaurs show adaptations towards powered flight (robust arms and shoulders with sites for large muscles) and the fossil record includes multiple pterosaurs with 7 metre wingspans found hundreds of miles of the then coastlines. Did they really swim all that way?

The take home message for me is that the authors have demonstrated that pterosaurs probably could not have flown like and albatross in some circumstances. But given that pterosaurs were not build like albatrosses, had adpatations towards powered flight that flat contradict some aspects of this study, may have had unknown adaptations towards efficient soaring we do not know about and we do not know much about the weather conditions of the time (perhaps there were consistent high-speed winds) most of the conclusions are either meaningless or something we have known for a very long time."

Here is a comment I got on my post on this same subject. I thought it might be helpful. It is from the one Dave Hone.

Christie Lynn said...

So in other words, Bryan, they're still as cool as I thought they were when I was a kid? :)

Anonymous said...

It might be enlightening to discover a Pterosaurian fossil on a small island where they presumably would not have survived as a terrestrial forager due to limited food resources... If there was minimal food and a number of their specie present as a breeding population the fossil record would show a reduction of their size over a short period of time (several hundred years could account for this, vis the 'mini-mammoths' bones found on that island off the coast of Canada. -Pony-sized mammoths... kewl!)

-Blown off course and stranded to die on a small island would suffice proof of flight. Or float..

Bryan W/a 'y' said...

Some more info I got in comments that might be interesting for you all:

There's a large diversity even among the biggest pterosaurs.

The extra-huge azhdarchids (such as Quetzalcoatlus and Hatzegopteryx) seem to have been stork analogues -- finding their food by walking across the countryside --, but they were very clearly able to fly. First, they had very, very powerful wings with attachment sites for huge muscles that weren't useful for anything else. They clearly flapped a lot -- unlike an albatross. Second, they had special adaptations for a very powerful launch: they were able to get off the ground in no time. And third, what is this kind of animal supposed to have done, other than launching, when a tyrannosaur came?

Pteranodon is a different beast. Small, weak hindlimbs, and hundreds of skeletons found hundreds of km away from the nearest coastline. Must have flown there, which -- again -- fits the anatomy of its wings and chest. Apparently it just didn't fly in the exact same way as an albatross.

And that's by no means an exhaustive list of the pterosaurs that surpassed the "maximum size" found by Sato et al..

The experts thrash this paper pretty impressively. Basically, it's a failure of peer review. Start here, click "next by date" a few dozen times ("next by thread" is unreliable), and then move on to the next month.


Sam said...

Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the legs to a dramatically lengthened fourth finger. Pterosaurs were an order of flying reptiles that lived during the time of the dinosaurs. Pterosaurs could flap their wings and fly with power, but the largest ones probably relied on updrafts (rising warm air) and breezes to help in flying.