Scientists described two fossilized birds from the Jurassic period in a recent article published in the journal Nature on Wednesday, marking a "historic" discovery. Unearthed in the Zhenghe region of Fujian province in southeastern China, one of the fossils belongs to a bird species the size of a quail, named Baminornis zhenghensis, which lived approximately 150 million years ago.
"Until now, the oldest record of short-tailed birds dated from the Early Cretaceous. Baminornis zhenghensis is the only short-tailed Jurassic bird and the oldest discovered so far, which pushes back the appearance of this derived characteristic of birds by almost 20 million years," said Professor Wang Min, lead author from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences.
The fossil of Baminornis zhenghensis reveals that it had a short tail ending in a fused bone called a pygostyle, an aerodynamic innovation that helps move the center of mass of the body forward toward the wings. This feature is also observed in living birds and has aerodynamic functions [https://www.sci.news/paleontology/baminornis-zhenghensis-13664.html]. The presence of a pygostyle in such an ancient bird indicates that advanced avian features evolved earlier than previously thought.
Baminornis zhenghensis displays a combination of features, including derived ornithothoracine bird-like shoulder and pelvic girdles, and it possessed modern features. These characteristics suggest the role of mosaic evolution in early bird development.
In their new study, Professor Wang and co-authors discovered and examined the fossils of two early birds, which were part of the so-called Zhenghe biota, filling a spatiotemporal gap in the early evolutionary history of birds.
The second fossil discussed in the study is incomplete, consisting solely of a furcula—a bird bone resembling a fork, formed by the fusion of both clavicles. The researchers performed geometric morphometric and phylogenetic analyses to explore the relationship of the furcula with other non-avialan and avialan theropods. However, due to its poor preservation, the team refrained from naming a new taxon based on this single bone and could not taxonomically place the furcula in the bird record.
The results supported the referral of this furcula to Ornithuromorpha, a diverse group of Cretaceous birds. The placement of the furcula within birds needs further fossil evidence, but these findings suggest a greater diversity of early birds than previously recognized.
These discoveries have implications for understanding avian evolution. Birds are the most diverse group of terrestrial vertebrates, yet their earliest evolutionary history has long been obscured by a fragmentary fossil record, which has hindered studies in this area. The new fossils help fill gaps in this record.
Archaeopteryx, previously considered the only widely accepted Jurassic bird, had feathered wings but closely resembled non-avialan dinosaurs due to its distinctive long, reptilian tail. This contrasts with the short-tailed morphology of modern and Cretaceous birds. Recent studies have questioned the avialan status of Archaeopteryx, classifying it as a deinonychosaurian dinosaur, the sister group to birds. This raises the question of whether any unambiguous records of Jurassic birds exist.
"If we take a step back and reconsider the phylogenetic uncertainty of Archaeopteryx, we have no doubt that Baminornis zhenghensis is the true Jurassic bird," said Dr. Zhou Zhonghe from the Institute of Vertebrate Paleontology and Paleoanthropology, co-author of the study, according to El Nuevo Día.
Stephen Brusatte from the University of Edinburgh noted the importance of this discovery. "Baminornis zhenghensis resembles modern birds more than Archaeopteryx," he explained. "It could even have been a better flyer than some other primitive birds several million years later, from the Cretaceous," Brusatte stated.
The article was written with the assistance of a news analysis system.