Julia Clarke’s interests were eclectic from the start. At nine she read Lost Horizon, by John Hilton, and decided she wanted to live out her days as a writer buried in a tiny, hidden village in the Himalayas.

“When I was 15, I told my parents I wanted to go to Tunisia – I needed to see Carthage,” she says.

Her parents never took her there, but they did go to Morocco and Italy. In high school, she got into sculpture and volunteered on archaeology sites where she studied ancient Polynesian culture on Hawai'i and early humans in the Mediterranean Basin.

At Brown University, she created her own major around the history of science and comparative Spanish literature, and then planned to work toward a PhD in philosophy of science and settle into a career of pondering the arc of human discovery.

But that was before she started digging for bones.

Today, Clarke is one of the world’s leading experts on the branch of dinosaurs that eventually became birds – and she's as eclectic as ever. When you enter her office on the Austin campus of the University of Texas, you think you’ve come upon either a lifelong bird fanatic or a dinosaur fan who never grew up. Her walls are covered with elegant sketches of sauropod bones and vintage paintings of birds. Several plastic and cloth toy dinosaurs perch in her window.

But you would be wrong. “I was not a dinosaur fangirl. Or a bird one,” she says, chuckling at the toys. The toys – which she’s picked up around the world – aren’t for her amusement, but rather serve as a reminder of all humanity’s fascination with these creatures. “What’s my favorite dinosaur?” Clarke asks, with a shrug. “It’s the one I’m working on right now.”

Clarke wants to understand how dinosaurs became birds and what that evolution tells us about modern-day birds. But rather than focus on just one piece of this paleontological puzzle, she asks broad, far-ranging questions about movement, coloration, and, most recently, vocalizations. Her study requires complex collaborations with all kinds of experts outside of paleontology, such as biologists, geneticists, and engineers. But most of all it requires a nimble, eclectic mind. 

To understand Clarke’s career, one must understand that it’s more about the question than the creature. For instance, late during her years at Brown she studied the Chicxulub crater on the Yucatan Peninsula which, in 1990, had been linked to a massive asteroid impact that ended the Cretaceous Period by killing off all the dinosaurs except those that evolved into birds (the so-called K-Pg extinction event).

“Why do all other dinosaurs go extinct at the K-Pg boundary?” Clarke asks. “There were all these different flying dinosaurs by the end of the Cretaceous Period, but only species in one group survived.” 

Imagine an event that could wipe out a dominant and diverse group of animals like that – essentially reshaping life on Earth. What would allow an animal to escape such a fate? Feathers? Fur? Flight? Plenty of other dinosaurs had feathers and even wings. We’re still not sure what the answer is, but with Clarke’s help, we now have some of the right questions. 

To try to find an answer, Clarke, at the end of her graduate studies in the late 1990s, looked at the fossils of early bird-like creatures, such as Ichthyornis dispar (“fish bird,” which resembled a seagull with teeth) and Apsaravis ukhaana (a sort of dove-like species from Mongolia). Her examination of the latter animal with paleontologist Mark Norell led her to essentially rewrite the family tree for all the ancestral birds going back 200 million years before the K-Pg extinction. In a single sweep she erased a dozen traits previously thought crucial to identifying modern birds, and upended the belief held at the time that those dinosaur survivors were only found along shorelines.

Clarke and Norell published their findings in 2001 in the journal Nature. The paper laid the groundwork for Clarke’s later work, allowing her to see a broader picture – the relationships among all the animals she was studying. It was the third among more than 75 scientific papers she has published over the past 16 years and the first of 10 papers in either Nature or Science. Her research findings have also been featured in The Origin of Birds, one of a trilogy of Great Transitions films produced for the classroom by HHMI’s BioInteractive educational resources group.

Early on, Clarke became an expert in phylogenies, or evolutionary trees, and has produced more than a dozen papers organizing and reorganizing these trees using data from fossilized bones from around the world. But when one studies the relationships among dinosaur fossils, one can’t help but fill in muscles and soft tissue. So, not surprisingly, Clarke soon became fascinated with how the bird-dinosaurs moved.

When Clarke talks about evolution, the adaptations that separate one animal from another on her phylogenic trees, she often sounds as if she’s describing a Silicon Valley start-up. Every change that led to flight is an “innovation” in her parlance. In some sense, that’s what she’s dedicated her life to – the study of animal innovation. 

So what led to one of the greatest innovations in the history of life on the planet? What in the dinosaur body led to flying birds? Certainly, movement and body design are at the top of the list. Clarke has looked at the earliest examples of the fan-like tail that flying dinosaurs used to stay stable in the air as well as the size of the animal – consistently small-framed. She also helped overturn the commonly repeated supposition that feathers arose to power flight. Far from it, in fact: rudimentary feathers existed 100 million years before flight, during the early days of dinosaurs.

“Feathers evolved for some other purpose,” Clarke says. “There’s an independent event that led to diversification in body coverings that has nothing to do with flight. It has to do with changes in locomotion in a different, earlier period close to the start of the age of dinosaurs.”

Early feather-like structures, Clarke found, seemed to be just one of a suite of coverings seen in early reptiles that shows a more upright posture and higher metabolic rates. They were one tool in a diverse kit of innovations dinosaurs came up with to regulate body temperature, attract mates, or perhaps even to sense the world around them.

From there, Clarke got hooked on penguins, discovering the earliest species from South America. Following her interest in how novel ways of moving evolve, she looked at how fossils and the penguin evolutionary tree might tell us how a wing for flight could turn into a flipper for swimming. She asked how losing flight and gaining wing-propelled diving shaped all parts of the body from sensory systems to body coverings.

And then back to feathers. In 2004 a colleague discovered a truly massive penguin fossil in Peru (the creature would have been twice the weight of an emperor penguin). Painstakingly removing layers of the rock surrounding part of the fossil, Clarke found layers of tiny, popsicle stick-shaped wing feathers. Analysis showed that these approximately 40 million-year-old feathers were brown or reddish in color, and arranged like those of a living penguin. 

This work led Clarke to wonder how the modern penguin ended up in a shimmering black tuxedo. She combed the literature and was shocked to find that no one had ever bothered to look inside a penguin feather and ask. So she turned to a new technique for looking at microscopic, light-absorbing structures called melanosomes.

Melanosome shapes were known to vary in birds of different brown, black, gray, and iridescent colors. Her team found that melanosomes in living penguins were bizarre compared with all other birds – arranged like clusters of grapes and unusually round. This took Clarke down a new rabbit hole of investigation: bird and dinosaur coloration, an area that has seen tremendous attention over the past decade or so. 

She and collaborators in the U.S. and China even found that some feathered dinosaurs had long, skinny melanosomes that – as in ducks and pheasants – create a shine from a gloss to dazzling bright green, blue, and reddish colors. Why? Well, why does any critter need to sparkle? To attract a mate. 

“Sexual selection seemed to be really important in dinosaurs, especially right around the origin of flight and the origin of [modern] feathers,” she says.

When it comes to evolution, sex is paramount. The selection of mates determines which innovations continue and which disappear. Imagine a bright green parrot for a moment, sweeping from side to side, flashing shimmering feathers in the setting sun, hoping to catch the eye of a female. Millions of innovations were passed down from his dinosaur ancestors, working together to ensure a next generation. Except there is one piece missing from that picture – one more innovation Julia Clarke decided to follow down one more rabbit hole.

“The whole thing started when she saw something in a fossil that other people hadn’t seen,” says Clifford Tabin, a renowned Harvard University geneticist now working with Clarke. “Other people had sort of ignored it and just looked at beaks and legs.” 

That fossil was Vegavis, an ancient sort of duck that lived not long before the K-Pg asteroid slammed into Earth. What Clarke saw was the animal’s voice box. It’s hard enough to pick out a feather or a shoulder bone from a fossil that’s been squashed in mud for 70 million years. But spotting a voice box is nearly impossible. That’s because, unlike the human larynx located in the throat, the structure birds use to vocalize, the syrinx, is buried deep in the chest, just above the lungs. This fossil syrinx, Clarke figured, might be the key to understanding the dinosaur voice and, eventually, bird voices.

“If you’ve got a voice box that makes a quack, a voice box that makes a cheep, and a voice box that makes a honk, how do the different shapes of the boxes affect the different sounds?” Tabin asks.

As with the iridescent feathers, Clarke is convinced that form is related to function, and the key to understanding both is to blend the old with the new. For feathers, longer melanosomes correlated to structures in modern birds that refract light. To understand the evolution of sound in dinosaurs, she will attempt to parse the relationship between shape and sound in modern birds. 

This time, Clarke has assembled a truly eclectic group of scientists from around the world, from Germany to Idaho. Engineers, geneticists, experts in the sound-making of the living, experts in the long dead, all puzzling over complex 3D scans of bird syrinxes from across the bird world. And at the center sits Clarke, a thousand new questions popping in her head.

At the end of the day, Clarke is a tricky person to fit into any niche. She’s not a bird behavior expert, nor is she driven by new dinosaur discoveries, although she’s worked a lot in these areas. She’s equally comfortable in a lab or at an Antarctic dig site. Her synthetic research blends paleontology, genetics, animal behavior, and evolutionary theory.

What unifies her work is her boundless curiosity. For the past two decades she has followed a series of questions, each leading to a new one, and each offering a broader understanding of how one group of small dinosaurs survived the devastating K-Pg extinction and evolved into modern birds. 

“She has a talent for identifying the really interesting questions – the ones that nobody has ever asked before,” says Johannes Müller, an expert in reptile evolution at the Museum of Natural Sciences in Berlin who’s working with Clarke on the syrinx research.

More than anything, that’s what makes Clarke’s work so interesting. Her questions force her to take things that can fossilize – like bones, melanosomes, or syrinxes – and use them to understand things that don’t – like behavior or song. And it’s these evanescent traits that can drive evolution.

From the eclectic girl captivated by John Hilton’s world to the scientist she is today, Julia Clarke has never lost her most compelling characteristic: she’s indifferent to all boundaries. When she a question gets stuck in her head, she pursues it wherever it leads.

Her ability to bring together disparate fields has brought her to ask questions that few other paleontologists would. It’s helped her to reshape family trees, understand movement and feathers, and come closer to understanding that special thing that allowed birds to become the most diverse vertebrates on the planet (twice as diverse as mammals). It’s brought her to dig up long-dead creatures in nine countries and on six continents.

“Julia is a transformative figure in ornithology, and I don’t say that lightly,” says Shannon Hackett, a curator at Chicago’s Field Museum who has worked with Clarke for years. “And she’s very collaborative – that’s one of her strengths. Collaborative not just with people but also with completely different disciplines of science. That’s her nature,” Hackett says, “and that’s, I think, her special gift.” ■

Story by Erik Vance
Photography by Aggie Brooks