‘Leggy bird’ complicates avian-dinosaur relationship

7 Sep 2023

Reconstruction of the 150m-year-old avialan theropod Fujianvenator prodigiosus. Image: Zhao Chuang

Researchers in China have found a Jurassic bird ancestor which provides a missing link in the evolutionary connections between dinosaurs and our modern flying friends.

A fossil discovered in the Fujian province of China provides key evidence in a sparse record about the early evolution of birds.

Described in a paper published in Nature yesterday (6 September), Fujianvenator prodigiosus is roughly 150m years old and is one of the youngest and geographically southernmost Jurassic avialans (the family of birds and their dinosaur relatives) ever discovered.

Birds are descended from theropod (hollow-boned) dinosaurs of the Jurassic period, which extended from about 145 to 201m years ago. Many scientists believe the now famous Archaeopteryx lithographica, which was discovered in Germany, to be the first bird ancestor capable of flight. It is also about 150m years old.

The discovery of Fujianvenator adds to mounting evidence that bird ancestors had already started diversifying before Archaeopteryx flew onto the scene.

Fujianvenator is described as the size of a koklass pheasant, weighed an estimated 641g and was young when it died. It doesn’t appear to have been capable of flight.

It had “unusually elongated lower legs”, and this and other attributes make it distinct from all avialan and non-avialan theropods of the era.

The fossil was found in an area that would have been swamp, a previously unknown habitat for early birds, and researchers believe its long lower legs indicate it may have been a fast runner or it could have waded in swamps. Unfortunately, because the digits on the fossil are poorly preserved, it was not possible to exam them for signs of webbing.

“Our comparative analyses show that marked changes in body plan occurred along the early avialan line, which is largely driven by the forelimb, eventually giving rise to the typical bird limb proportion,” said Dr Wang Min from the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) at the Chinese Academy of Sciences in Beijing, who is co-lead author of the study.

“However, Fujianvenator is an odd species that diverged from this main trajectory and evolved bizarre hindlimb architecture.”

Alongside Fujianvenator, researchers found a variety of swamp creatures and have referred to this find as the Zhenghe fauna. These include fish, turtles and other aquatic reptiles.

According to researchers, “the discovery of the Zhenghe fauna opens a new window into the Late Jurassic terrestrial ecosystem of the planet”.

The team from the IVPP and the Fujian Institute of Geological Survey plan to continue their exploration of Zhenghe and nearby areas in hopes of finding more pieces to add to the dinosaur-bird puzzle.

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Rebecca Graham is production editor at Silicon Republic