7/30/2019 Ngo 20130426 Bird

1/4

Birds' " Crouching" Gait Born in Dinosaur

Ancestors

Getting closer to the ground helped dinosaurs take flight, says a new study.

The ancestors of modern birds developed a crouched stance to compensate for larger forelimbs,

or wings.

Illustration courtesy Luis Rey

Brian Handwerk

forNational Geographic News

Published April 24, 2013

Watch a bird's odd, bent-legged gait and you'll see anevolutionary adaptationborn millions of

years ago in itsdinosaurancestors while they were still confined to the ground.

The crouched stance developed to compensate for the growth of larger forelimbs that eventually made

flight possible, according to new research that digitally "fleshed out" fossils to show physical changes

http://news.nationalgeographic.com/http://news.nationalgeographic.com/http://news.nationalgeographic.com/http://www.pbs.org/wgbh/evolution/library/03/4/l_034_01.htmlhttp://www.pbs.org/wgbh/evolution/library/03/4/l_034_01.htmlhttp://animals.nationalgeographic.com/animals/prehistoric/http://animals.nationalgeographic.com/animals/prehistoric/http://animals.nationalgeographic.com/animals/prehistoric/http://animals.nationalgeographic.com/animals/prehistoric/http://www.pbs.org/wgbh/evolution/library/03/4/l_034_01.htmlhttp://news.nationalgeographic.com/

7/30/2019 Ngo 20130426 Bird

2/4

over the eons as bipedal dinosaurs evolved into birds. (Read about the evolution of feathers in National

Geographic magazine.)

Birds and humans are the most common bipedal species in the modern world, but their legs are strikingly

different. Humans are basically straight-legged, which allows their bones to support their resting body

weight. But bird legs are bent into a zigzag, putting them in a crouched position that requires much more

muscular effort to stand.

"It's more efficient to bear weight passively, in a straight line down your long bones [like] a pillar," said

Vivian Allen of the Royal Veterinary College's Structure and Motion Labat the University of London, and

co-author ofa study published this weekin the journal Nature.

"In a crouch you have to use your muscles a lot more to resist gravity. Think about how much easier it is

to hold something when you're standing up straight than it is when you are crouched down. So if you

were designing an animal, this seems slightly odd from the perspective of mechanical principles."

(Related:"Baby Dinosaurs Flexed Muscles Inside Their Eggs.")

Surprising Results

To uncover the origins of this odd stance, Allen's team used fossils to create 3-D skeletons of

17 archosaurs, a group that includes both dinosaurs and living land animals like birds. They then digitally

fleshed out their bodies, using detailed muscular reconstructions and estimates taken from CT scans of

living relatives, to reproduce the body shapes of the extinct animals.

The results allowed the team to trace biomechanical changes over time from 245-million-year-old,

crocodile-like quadrupeds, to the earliest winged and feathered dinosaur Archaeopteryx 150 million years

ago, to modern birds like the red junglefowl (Gallus gallus).

Big, heavy-tailed beasts likeTyrannosaurus rexgave way to animals with thinner or shorter tails. And

although this most obvious physical change has long been noted, the new research suggests these

modifications didn't drive the development of modern bird posture as was commonly believed.

"We'd never doubted the hypothesis that the tail was responsible for the major changes in dinosaur

balance and posture," co-author and Royal Veterinary College evolutionary biomechanics expert J ohn R.

Hutchinson said in a statement.

"The tail is the most obvious change if you look at dinosaur bodies. But as we analyzed, and reanalyzed,

and punishingly scrutinized our data, we gradually realized that everyone had forgotten to check what

influence the forelimbs had on balance and posture, and that this influence was greater than that of the

tail or other parts of the body."

The enlarged forelimbs that gave rise to a crouching posture, and eventually flight, can be seen in winged

dinosaurs likeMicroraptorandArchaeopteryx, and in the featheredVelociraptor. (Pictures: "Dinosaur's

Flashy Feathers Revealed.")

"The point we found is that if you get these big forearms, it does change the way your hind legs work as

well," Allen explained. There's a pretty good statistical relationship between increasing limb mass and the

position of a dinosaur's center of mass, he added, but none between the location of the center of mass

and the mass of the tail.

http://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://www.rvc.ac.uk/SML/http://www.rvc.ac.uk/SML/http://www.google.com/url?q=http%3A%2F%2Fwww.rvc.ac.uk%2FSML%2F&sa=D&sntz=1&usg=AFQjCNEaTYC5TeCKAzk_i_iv5M77-kiMUAhttp://www.google.com/url?q=http%3A%2F%2Fwww.rvc.ac.uk%2FSML%2F&sa=D&sntz=1&usg=AFQjCNEaTYC5TeCKAzk_i_iv5M77-kiMUAhttp://dx.doi.org/10.1038/nature12059http://dx.doi.org/10.1038/nature12059http://dx.doi.org/10.1038/nature12059http://news.nationalgeographic.com/news/2013/13/130410-lufengosaurus-oldest-baby-dinosaur-embryo-paleontology/http://news.nationalgeographic.com/news/2013/13/130410-lufengosaurus-oldest-baby-dinosaur-embryo-paleontology/http://news.nationalgeographic.com/news/2013/13/130410-lufengosaurus-oldest-baby-dinosaur-embryo-paleontology/http://www.ucmp.berkeley.edu/diapsids/archosauria.htmlhttp://www.ucmp.berkeley.edu/diapsids/archosauria.htmlhttp://www.ucmp.berkeley.edu/diapsids/archosauria.htmlhttp://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://www.rvc.ac.uk/Staff/jhutchinson.cfmhttp://www.rvc.ac.uk/Staff/jhutchinson.cfmhttp://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://news.nationalgeographic.com/news/2012/03/pictures/120309-microraptors-dinosaurs-iridescent-feathers-science-nature/http://news.nationalgeographic.com/news/2012/03/pictures/120309-microraptors-dinosaurs-iridescent-feathers-science-nature/http://www.google.com/url?q=http%3A%2F%2Fnews.nationalgeographic.com%2Fnews%2F2012%2F03%2Fpictures%2F120309-microraptors-dinosaurs-iridescent-feathers-science-nature%2F&sa=D&sntz=1&usg=AFQjCNFD2bsPbFGWqeLBovYFUS-YQAiGAAhttp://www.google.com/url?q=http%3A%2F%2Fnews.nationalgeographic.com%2Fnews%2F2012%2F03%2Fpictures%2F120309-microraptors-dinosaurs-iridescent-feathers-science-nature%2F&sa=D&sntz=1&usg=AFQjCNFD2bsPbFGWqeLBovYFUS-YQAiGAAhttp://www.google.com/url?q=http%3A%2F%2Fnews.nationalgeographic.com%2Fnews%2F2012%2F03%2Fpictures%2F120309-microraptors-dinosaurs-iridescent-feathers-science-nature%2F&sa=D&sntz=1&usg=AFQjCNFD2bsPbFGWqeLBovYFUS-YQAiGAAhttp://www.google.com/url?q=http%3A%2F%2Fnews.nationalgeographic.com%2Fnews%2F2012%2F03%2Fpictures%2F120309-microraptors-dinosaurs-iridescent-feathers-science-nature%2F&sa=D&sntz=1&usg=AFQjCNFD2bsPbFGWqeLBovYFUS-YQAiGAAhttp://news.nationalgeographic.com/news/2012/03/pictures/120309-microraptors-dinosaurs-iridescent-feathers-science-nature/http://news.nationalgeographic.com/news/2012/03/pictures/120309-microraptors-dinosaurs-iridescent-feathers-science-nature/http://news.nationalgeographic.com/news/2012/03/pictures/120309-microraptors-dinosaurs-iridescent-feathers-science-nature/http://news.nationalgeographic.com/news/2012/03/pictures/120309-microraptors-dinosaurs-iridescent-feathers-science-nature/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://animals.nationalgeographic.com/animals/prehistoric/velociraptor-mongoliensis/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://news.nationalgeographic.com/news/2012/01/120124-dinosaurs-feathers-archaeopteryx-science-wings/http://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://news.nationalgeographic.com/news/2012/11/121105-microraptor-dinosaurs-flying-wings-paleontology-science/http://www.rvc.ac.uk/Staff/jhutchinson.cfmhttp://www.rvc.ac.uk/Staff/jhutchinson.cfmhttp://www.rvc.ac.uk/Staff/jhutchinson.cfmhttp://www.rvc.ac.uk/Staff/jhutchinson.cfmhttp://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://animals.nationalgeographic.com/animals/prehistoric/tyrannosaurus-rex/http://www.ucmp.berkeley.edu/diapsids/archosauria.htmlhttp://www.ucmp.berkeley.edu/diapsids/archosauria.htmlhttp://www.ucmp.berkeley.edu/diapsids/archosauria.htmlhttp://news.nationalgeographic.com/news/2013/13/130410-lufengosaurus-oldest-baby-dinosaur-embryo-paleontology/http://dx.doi.org/10.1038/nature12059http://dx.doi.org/10.1038/nature12059http://dx.doi.org/10.1038/nature12059http://www.google.com/url?q=http%3A%2F%2Fwww.rvc.ac.uk%2FSML%2F&sa=D&sntz=1&usg=AFQjCNEaTYC5TeCKAzk_i_iv5M77-kiMUAhttp://www.google.com/url?q=http%3A%2F%2Fwww.rvc.ac.uk%2FSML%2F&sa=D&sntz=1&usg=AFQjCNEaTYC5TeCKAzk_i_iv5M77-kiMUAhttp://www.rvc.ac.uk/SML/http://www.rvc.ac.uk/SML/http://www.rvc.ac.uk/SML/http://www.rvc.ac.uk/SML/http://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-texthttp://ngm.nationalgeographic.com/2011/02/feathers/zimmer-text

7/30/2019 Ngo 20130426 Bird

3/4

To imagine how the adaptation occurred, Allen said, you must remember that a biped's foot position is

strongly related to its center of mass.

"You might imagine a seesaw," he said. "If you move the hinge point of the seesaw you also have to

move the support base of it. So you need to have your feet pretty well under the center of mass."

If you move that center of mass forwardwhich is what happens with larger forelimbs like wingsyou

also have to move your foot forward, continued Allen. "And that means that the limb has to bend at the

joints and become more crouched. If you look at an ostrich or an emu, you'll see a femur that's almost

horizontal and very short." Led street light

The Journey to Flight

Hans-Dieter Sues, curator of vertebrate paleontology at the Smithsonian's National Museum of Natural

History in Washington, D.C., wasn't involved in the study but said he found the analysis quite compelling.

"Past studies had focused on the change in tail length, but this new paper is the first to look at the impact

of the forelimbs on posture," he said.

What he liked about the study, Sues added, was the fact that the researchers tracked the changes in

posture in the context of the evolutionary history of early birds and their dinosaur relatives.

The growing forelimbs appeared well before any dinosaurs took flight, so other needs drove their initial

development.

"The forelimbs presumably changed in length in the stem group of birds for the purpose of seizing and/or

manipulating prey," Sues said. He noted, however, that these changes were a significant step on the

road to flight.

The long forelimbs definitely became wings in birds, he said, and "the tails became reduced as other

flight adaptations in the skeleton developed."

Allen said a future study might reveal more about how some dinosaurs finally got off the ground by

looking at how the center of lift evolved with early gliders and flyers. "That's more difficult and you really

need to have an idea of the shape and size of the feathers," she said. "But enough specimens exist that

someone could give it a go."

Share on emailMore

2 commentsSign in

Post comment as...

Newest | Oldest | Top Comments

mark Riggle

16 hours ago

Birds do have a different bipedal gait than MOST humans. Children with cerebral palsy walk

with one of 3 gaits; none of them is what is considered the typical human adult gait. The most

http://yahamlighting.com/http://yahamlighting.com/http://paleobiology.si.edu/staff/individuals/sues.htmlhttp://paleobiology.si.edu/staff/individuals/sues.htmlhttp://news.nationalgeographic.com/news/2013/13/130424-dinosaurs-birds-flight-paleontology-evolution-science/http://news.nationalgeographic.com/news/2013/13/130424-dinosaurs-birds-flight-paleontology-evolution-science/https://members.nationalgeographic.com/9608811/https://members.nationalgeographic.com/9608811/https://members.nationalgeographic.com/9608811/https://members.nationalgeographic.com/9608811/http://news.nationalgeographic.com/news/2013/13/130424-dinosaurs-birds-flight-paleontology-evolution-science/http://news.nationalgeographic.com/news/2013/13/130424-dinosaurs-birds-flight-paleontology-evolution-science/http://paleobiology.si.edu/staff/individuals/sues.htmlhttp://yahamlighting.com/

7/30/2019 Ngo 20130426 Bird

4/4

common gait they adopt is a toe-walk. That gait is exactly the bird gait; in both the CP child and

the bird, the lower leg swings forward (and also somewhat inward for CP) until the toes jam

into the ground. This has two effects: the first is that the friction with the ground slows the

toe-area's forward speed; the second is the geometry of the foot and knee then greatly

increase the downward pressure which also greatly increases the friction with the

ground. That friction rapidly stops the foot's forward motion (like a hinged doorstop will do

when it drops with the door moving). It is a stop so rapid it creates a shockwave in the tibia and

then in the femur. Unfortunately, in CP children, that shockwave will eventually damage the

knee, and hip, and also twists the femur.

So the prior post asks the extremely relevant question: why (in a neural system way) did the

therapods (the bipedal archosaur group) become bipedal and walk they way they do? Does

that answer tell us why CP children walk that way? Interestingly, the other two gaits that are

adopted by CP children also have strong shockwave generating impact strikes (and those also

cause extreme joint and bone damage).

And now add on to that that the normal adult walking gait also produces a strong impact

shockwave from the heel strike. That shockwave travels up the skeleton and then in some

people may cause bone and joint problems (but much less than for CP for which it always

occurs). Even the human gaits found during development, from 1st toddler steps until the

mature adult gait is reached, all have this shockwave impact.

To me, a shockwave generating impact seems a pretty common geature for the bipeds. What

does that mean?