Nav: Home

Leg-wing cooperation in baby birds, dinosaurs is key transition in origin of flight

April 21, 2016

New research based on high-resolution x-ray movies reveals that despite having extremely underdeveloped muscles and wings, young birds acquire a mature flight stroke early in their development, initially relying heavily on their legs and wings to work in tandem to power the strenuous movement. The new study, published today in the journal PLOS ONE, is important for understanding the development of flight in modern birds and reconstructing its origins in extinct dinosaurs.

"The transition from ground-living dinosaurs to flight-capable birds is one of the major evolutionary transitions in vertebrate history, because flight is the most physically demanding form of locomotion," said lead author Ashley Heers, a postdoctoral researcher in the American Museum of Natural History's Division of Paleontology. "The kind of flight that we normally think of in living birds--for example, what you might see in a pigeon or a robin--involved a huge evolutionary overhaul of the animal's basic body plan over time. And although scientists have been studying flight for more a century, there's actually a surprising amount that we don't know about how birds fly."

Adult birds have many anatomical features that presumably help meet the demands of flight. However, juvenile birds, like the first winged dinosaurs, lack many hallmarks of advanced flight. Instead of large wings, they have small "protowings," and instead of robust, interlocking forelimb skeletons, their limbs are more gracile and their joints less constrained. These traits are often thought to preclude extinct theropods--the group of dinosaurs most closely related to modern birds--from powered flight, but young birds with similar rudimentary anatomies flap their wings as they run up slopes and even briefly fly, challenging longstanding ideas about the origin of flight.

To further explore this work, Heers and colleagues used a technique called x-ray reconstruction of moving morphology (XROMM)--which essentially produces a 3-D x-ray movie--to visualize skeletal movement in developing birds.

"For a long time, researchers weren't able to tell how birds were moving their skeletons because, of course, they are covered in feathers and muscles," Heers said. "This x-ray technique allows us to look at what's happening inside of the animals as they're performing different behaviors."

At Brown University, the researchers used XROMM to look at Chukar partridges (Alectoris chukar) at a variety of ages as they flapped their wings to help climb steep slopes--a behavior scientists call wing-assisted incline running (WAIR). They found that when flap-running at similar levels of effort, juvenile and adult birds show similar patterns of joint movement. Despite their undeveloped anatomy, young birds can produce all of the elements of the avian flight stroke and modify their wing stroke for different behaviors, just like adults.

How is this possible? The study suggests that the cooperation between a juvenile bird's legs and wings is key in early life: the force generated by flapping pushes the birds forward as well as upward, improving traction as they climb.

"When wings and legs are viewed in isolation, it is difficult to imagine how animals lacking flight adaptions could produce useful aerodynamic forces," Heers said. "However, flapping behaviors that involve cooperative use of wings and legs, like WAIR, require less muscle power and less aerodynamic force than level flight. Transitional behaviors therefore allow flight-incapable juveniles to transition to flight-capable adults in a continuous fashion, supplementing their underdeveloped wings and flight muscles with their legs until the flight apparatus can fully support body weight."

This wing-leg cooperation is a bridge between leg- and wing-based modes of locomotion. And the study indicates that extinct theropod dinosaurs might have done the same thing with their "mini-wings" before flight evolved.

"Baby birds anatomically look a lot like some of the dinosaur fossils that we see," Heers said. "And so, by studying baby birds and looking at how they actually use these dinosaur-like anatomies, we can get a better sense of how these long-extinct animals might have been using their wings."
-end-
Other authors on the paper include David Baier, Providence College; Brandon Jackson, Longwood University; and Kenneth Dial, University of Montana.

Funding for this study was provided by the National Science Foundation (NSF) Graduate Research Fellowship, award number GRFP-2007057068, NSF grant # 0919799, and by the W.M. Keck Foundation.

An XROMM video showing Chukar partridges of a variety of ages performing WAIR can be seen here: https://www.youtube.com/watch?v=ig_BPx0GLP8

AMERICAN MUSEUM OF NATURAL HISTORY (AMNH.ORG)

The American Museum of Natural History, founded in 1869, is one of the world's preeminent scientific, educational, and cultural institutions. The Museum encompasses 45 permanent exhibition halls, including the Rose Center for Earth and Space and the Hayden Planetarium, as well as galleries for temporary exhibitions. It is home to the Theodore Roosevelt Memorial, New York State's official memorial to its 33rd governor and the nation's 26th president, and a tribute to Roosevelt's enduring legacy of conservation. The Museum's five active research divisions and three cross-disciplinary centers support approximately 200 scientists, whose work draws on a world-class permanent collection of more than 33 million specimens and artifacts, as well as specialized collections for frozen tissue and genomic and astrophysical data, and one of the largest natural history libraries in the world. Through its Richard Gilder Graduate School, it is the only American museum authorized to grant the Ph.D. degree and the Master of Arts in Teaching degree. Annual attendance has grown to approximately 5 million, and the Museum's exhibitions and Space Shows can be seen in venues on five continents. The Museum's website and collection of apps for mobile devices extend its collections, exhibitions, and educational programs to millions more beyond its walls. Visit amnh.org for more information.

Follow

Become a fan of the Museum on Facebook at facebook.com/naturalhistory, and follow us on Instagram at @AMNH, Tumblr at amnhnyc, or Twitter at twitter.com/AMNH.

American Museum of Natural History

Related Dinosaurs Articles:

In the shadow of the dinosaurs
Research published this Wednesday in Scientific Reports describes Clevosaurus hadroprodon, a new reptile species from Rio Grande do Sul state in southern Brazil.
When the dinosaurs died, lichens thrived
When the asteroid hit, dinosaurs weren't the only ones that suffered.
Dinosaurs were thriving before asteroid strike that wiped them out
Dinosaurs were unaffected by long-term climate changes and flourished before their sudden demise by asteroid strike.
Did volcanoes kill the dinosaurs? New evidence points to 'maybe.'
Princeton geoscientists Blair Schoene and Gerta Keller led an international team of researchers who have assembled the first high-resolution timeline for the massive eruptions in India's Deccan Traps, determining that the largest eruption pulse occurred less than 100,000 years before the mass extinction that killed the (non-avian) dinosaurs.
Want to learn about dinosaurs? Pick up some Louisiana roadkill
Scientists are able to learn about an animal's ecosystem by studying the chemical makeup of its body, whether the animal died recently or millions of years ago.
More Dinosaurs News and Dinosaurs Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...