Duck Dynasty

 

New research tells us to forget everything we thought we knew about dinosaurs.

If a time machine dropped modern day humans onto Antarctica’s Vega Island around the end of the Cretaceous period, they might find the sounds of that ancient forest familiar. “You would hear chicken-like or duck-like noises,” as well as pigeon-like coos, says Julia Clarke, a vertebrate paleontologist and UT Jackson School of Geosciences professor. She’s participated in a wave of discoveries debunking conventional ideas about dinosaurs—including evidence that some of the prehistoric creatures were feathered, not scaly, and almost certainly didn’t roar.

Last year, Clarke published a paper on the discovery of a vocal organ, called a syrinx, in a fossil of a bird that lived in Antarctica at least 66 million years ago. The syrinx is similar to those found in modern birds, consisting of rings of cartilage covered in soft tissues that vibrate to produce sounds. Most dinosaur fossils from the same time period lack such vocal organs.

The find brings scientists a step closer to figuring out what ancient birds and their dinosaur predecessors sounded like. It also advances Clarke’s professional focus on how avian dinosaurs evolved into modern birds with traits such as complex songs, which their ancestors lacked. There are some 10,000 individual bird species—more than the number of all land-dwelling vertebrates and double the number of mammal species.“That is an amazing number of terrestrial animal species,” Clarke says. “Where did they come from?”

A 150 million-year-old Archaeopteryx fossil discovered in 1861 first established an evolutionary link between modern-day birds and ancient reptiles. Based on many other fossils, scientists have since concluded that today’s birds evolved from a group of dinosaurs called theropods, which had small forelimbs. Some of these survived the global mass extinction 66 million years ago that wiped out most dinosaurs.

In 1996, while attending her first scientific meeting as a new graduate student, Clarke heard about 120 million-year-old fossils found in China of a chicken-sized dinosaur called Sinosauropteryx. “It was covered in some primitive form of feathers. But this dinosaur couldn’t fly,” she says. “So why did it have feathers?” The question launched her quest to trace the development of bird traits.

Clarke joined a team of scientists that concluded the Microraptor, a four-winged, 120-million-year-old dinosaur, used its feathers for courtship, not flight. She also discovered ancient dinosaurs had the same forms of color pigment, called melanosomes, as living mammals and birds. That research hinted at specific colors for early feathered dinosaurs and suggested some became warm-blooded earlier than previously thought.

And when a paper published in December 2016 about a feathered dinosaur tail preserved in amber created quite the stir, Clarke noted that the specimen preserves feathers in three dimensional detail not present in fossils pressed in rock. But at 99 million years old, it is hardly the earliest evidence of feathered dinosaurs; that title more likely belongs to a 155 million-year-old fossil, Anchiornis Huxleyi (Clarke and colleagues mapped its feather colors in a 2010 paper).

In 2005, Clarke described a new species, Vegavis iaai, a relative of modern-day ducks, based on a fossil from Antarctica. Up until 30-plus million years ago, the continent remained ice-free and rich in flora and fauna, including dinosaurs. The Vegavis fossil, discovered on Vega Island in 1992 by scientists from the Argentine Antarctic Institute, is the only known skeleton related to modern bird species that also lived alongside dinosaurs.

Clarke collected fossils herself on an 18-day expedition to Antarctica’s James Ross archipelago in 2011. She returned five years later for a two-month expedition funded by a National Science Foundation grant. More than an important part of her research, the expeditions, while strenuous, represented a dream come true for Clarke. “As a kid, I loved finding things and I was heavily influenced by Indiana Jones movies—although his techniques were terrible,” she says. “I never had an obsession with dinosaurs, but I did want to travel the world and go to remote places.”

Between these expeditions, in 2013, Clarke began studying a new fossil that had been found on Vega Island. About the size of a grapefruit half, it contained a jumble of fossilized bones still embedded in rock, including a tiny one that she thought was a toe bone. Around the same time, Clarke talked with several other scientists about a research project to look at the evolution of vocalization and related fossil data. “Bird vocalization is unique compared to all land dwelling mammals,” she explains. “Their voice box is deep in the chest, while other animals have a voice box in the throat. I was thinking about why this novel method evolved and that made me wonder whether the Vega fossil had a syrinx.”

She took another look and realized that the small “toe” bone was, in fact, a syrinx. Its presence means this early bird ancestor could have filled ancient Antarctica with those familiar chicken- and duck-like sounds.

Clarke has since assembled a team of scientists to explore the development and function of the syrinx from multiple angles, including developmental biology, physiology, and engineering. In addition to a paper describing the syrinx discovery, the team has already published its conclusion that some dinosaurs vocalized even without a syrinx, making sounds with their mouths closed, much like modern doves—and accounting for the coos in that ancient forest scene.

The collaborators plan to continue studying the fossil record. They’ll also examine the way modern birds and crocodilians make sound and extrapolate those findings back to their extinct ancestors, dinosaurs.

“There is still a lot we have to figure out,” Clarke says. “This is not the end of the story but the beginning.”

Illustration by Matt Collins

 

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