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Missing link in pterosaur origins discovered

Lagerpetids, including the species Ixalerpeton (illustrated here), may be close relatives of pterosaurs.
Lagerpetids, including the species Ixalerpeton (illustrated here), may be close relatives of pterosaurs. (Image credit: Rodolfo Nogueira)

Nearly nothing is known about the family tree of pterosaurs — iconic reptiles that flew alongside the dinosaurs. These now-extinct beasts appear in the fossil record with already developed wings and senses adapted for flying, with researchers having nary a clue about their immediate evolutionary history.

But now, the pterosaur's family tree has a new branch; an enigmatic group of small reptiles, known as lagerpetids, might be the closest-known pterosaur relatives on record, the researchers of a new study say.

Unlike pterosaurs, however, lagerpetids did not fly. "Now, we have an idea of what a flightless pterosaur relative would look like," study co-researcher Sterling Nesbitt, an associate professor of geosciences at Virginia Tech, told Live Science. 

Related: Photos: Baby pterosaurs couldn't fly as hatchlings 

The first pterosaur fossils were described in 1784, and countless pterosaur remains have turned up since then, dating as far back as 220 million years during the Triassic period to about 65 million years ago, at the end-Cretaceous extinction. But beyond knowing that pterosaurs were archosaurs, a group that includes dinosaurs, birds and crocodylians, scientists haven't figured out the pterosaur's immediate ancestors — animals that could offer clues about how the pterosaur became the first vertebrate to evolve powered flight.

Although lagerpetids were Earth-bound, they do shed light on pterosaur flight, Nesbitt said. Researchers have published studies on lagerpetid fossils since the 1970s, but they didn't know much about this weird reptile, except that it lived from about 237 million to 210 million years ago, and that it was likely related to dinosaurs, which first appeared about 233 million years ago. After all, the lagerpetid hindlimb and pelvis did resemble that of a dinosaur, Nesbitt said. But then, researchers started finding more complete lagerpetid fossils in more places around the world, including a 237 million-year-old "tiny bug slayer" from Madagascar, and realized that these animals shared more in common with pterosaurs than with dinosaurs. 

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This small reptile, a lagerpetid known as Ixalerpeton, climbs a tree.

This small reptile, a lagerpetid known as Ixalerpeton, climbs a tree about 233 million years ago in what is now Brazil. (Image credit: Rodolfo Nogueira)
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Martín Ezcurra (left) and Sterling Nesbitt (right) collect reptile specimens from Triassic rocks at the Chañares Formation of northwest Argentina.

Martín Ezcurra (left) and Sterling Nesbitt (right) collect reptile specimens from Triassic rocks at the Chañares Formation of northwest Argentina. (Image credit: Courtesy Martín Ezcurra)
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The researchers excavate fossils at the Chañares Formation in Argentina.

The researchers excavate fossils at the Chañares Formation in Argentina. (Image credit: Courtesy Martín Ezcurra)
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A reconstruction of a lagerpetid skeleton.

A reconstruction of a lagerpetid skeleton. (Image credit: Courtesy Martín Ezcurra)
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Martín Ezcurra (left) and Sterling Nesbitt (right) hunt for fossils in northwest Argentina.

Martín Ezcurra (left) and Sterling Nesbitt (right) hunt for fossils in northwest Argentina. (Image credit: Courtesy Martín Ezcurra)
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The Triassic rocks of the Chañares Formation (grey and brown), in northwest Argentina, that held the remains of the lagerpetid Lagerpeton.

The Triassic rocks of the Chañares Formation (grey and brown), in northwest Argentina, that held the remains of the lagerpetid Lagerpeton. (Image credit: Courtesy Martín Ezcurra)
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The Chañares Formation, where lagerpetid fossils were found.

The Chañares Formation, where lagerpetid fossils were found. (Image credit: Courtesy Martín Ezcurra)
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The location in Argentina where researchers found the lagerpetid Lagerpeton.

The location in Argentina where researchers found the lagerpetid Lagerpeton. (Image credit: Courtesy Martín Ezcurra)
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A partially prepared specimen (showing the trunk and tail vertebrae, pelvic girdle, and hindlimb) of the lagerpetid Lagerpeton from the Triassic Chañares Formation of Argentina.

A partially prepared specimen (showing the trunk and tail vertebrae, pelvic girdle, and hindlimb) of the lagerpetid Lagerpeton from the Triassic Chañares Formation of Argentina. (Image credit: Courtesy Martín Ezcurra)

In addition, researchers used a micro-CT (computed tomography) scan to analyze a lagerpetid braincase, where the brain sat. The results showed that lagerpetids and pterosaurs had similarly shaped brains and inner ears, so some of the pterosaur's specialized sensory systems likely evolved before powered flight. 

"It has to do with the semicircular canals [in the ear], which orients you in 3D space," Nesbitt said. "The shape of those canals correlates with ecology and how you move your head — basically, are you agile or not? And a lot of things that have flight have semicircular canals with a really large and characteristic [shape] because you're flying, you're in a lot more 3D space." 

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About 212 million years ago, in what is now Ghost Ranch, New Mexico, a species of lagerpetids known as Dromomeron romeri grabbed a drink while several pterosaurs fly overhead.

About 212 million years ago, in what is now Ghost Ranch, New Mexico, a species of lagerpetids known as Dromomeron romeri grabbed a drink while several pterosaurs fly overhead. (Image credit: Stephanie Abramowicz/Dinosaur Institute, NHMLAC)
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A field team excavates fossils from the Late Triassic Hayden Quarry at Ghost Ranch in 2018.

A field team excavates fossils from the Late Triassic Hayden Quarry at Ghost Ranch in 2018. (Image credit: Nathan Smith/Dinosaur Institute, NHMLAC)
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Triassic outcrops of the Chinle Formation of New Mexico, which held the fossils of the lagerpetid Dromomeron.

Triassic outcrops of the Chinle Formation of New Mexico, which held the fossils of the lagerpetid Dromomeron. (Image credit: Courtesy Martín Ezcurra)
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The site where researchers found the lagerpetid Dromomeron.

The site where researchers found the lagerpetid Dromomeron. (Image credit: Courtesy Martín Ezcurra)
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The lower left jawbone of the lagerpetid Ixalerpeton, from the Triassic Santa Maria Sequence of southern Brazil.

The lower left jawbone of the lagerpetid Ixalerpeton, from the Triassic Santa Maria Sequence of southern Brazil. (Image credit: Courtesy Martín Ezcurra)
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The lower left right jawbone of the lagerpetid Ixalerpeton, from the Triassic Santa Maria Sequence of southern Brazil.

The lower right jawbone of the lagerpetid Ixalerpeton, from the Triassic Santa Maria Sequence of southern Brazil. (Image credit: Courtesy Martín Ezcurra)

Lagerpetids, however, are not the direct ancestors of pterosaurs. If you think of a family tree shaped like a "Y," the lagerpetids and pterosaurs are on different "arms" of the Y, but share a common ancestor at the Y's base.

The study "provides some impressive evidence," but "some difficult questions remain," said David Unwin, a reader in paleobiology at the University of Leicester in England who studies pterosaurs, but wasn't involved with the study. 

"Lagerpetids, argued in this analysis to be the closest known relatives to pterosaurs, were small, lightly-built, fully bipedal [two-legged] animals with relatively short forelimbs," Unwin told Live Science in an email. "Pterosaurs, by contrast, were fully quadrupedal [four-legged] and had highly elongate[d] forelimbs." In other words, there's a huge difference in the body shapes of lagerpetids, pterosaurs and dinosaurs, and "these discoveries throw little light on when, where and how pterosaurs and their flight ability first evolved," Unwin said.

The study was published online Wednesday (Dec. 9) in the journal Nature

Originally published on Live Science.

Laura Geggel
As an associate editor for Live Science, Laura Geggel covers general science, including the environment, archaeology and amazing animals. She has written for The New York Times, Scholastic, Popular Science and Spectrum, a site covering autism research. Laura grew up in Seattle and studied English literature and psychology at Washington University in St. Louis before completing her graduate degree in science writing at NYU. When not writing, you'll find Laura playing Ultimate Frisbee.