This undated handout photo shows two images together with an interpretive line drawing of the "Chicago Archaeopteryx," a specimen collected by the Field Museum of Natural History in Chicago, the United States. (Chinese Academy of Sciences/Handout via Xinhua)BEIJING, May 15 (Xinhua) -- A new study led by researchers from China and the United States has unveiled a well-preserved specimen of Archaeopteryx -- widely accepted as the most primitive bird. The study discovered new details about the bones, soft tissues and feathers of the species.The findings, published in Nature on Wednesday, provide crucial evidence of the skull evolution and flight adaptations the species underwent during its transition from dinosaur to bird.Collected by the Chicago-based Field Museum of Natural History in 2022, the pigeon-sized specimen analyzed in the study is the world's 14th Archaeopteryx ever found -- and the smallest. The researchers have designated it the "Chicago Archaeopteryx."The specimen is intact, with most of its bones well-preserved. It also has rare soft tissues such as skin, toe pads and feathers, making it a landmark specimen in the research of early bird evolution, the study noted.Through high-resolution CT scans and digital 3D reconstruction, the researchers found that almost the entire skull of the specimen is preserved, including the palatal region, which is the roof of the mouth area.The skull's shape is somewhere between that of troodontids -- bird-like theropod dinosaur that inhabited Earth from the Late Jurassic to the Late Cretaceous period -- and those of more derived Cretaceous birds."This represents a critical evolutionary stage in the transition from the rigid, immobile skulls of non-avian dinosaurs to the more lightweight and flexible skulls of birds," said lead researcher Hu Han from the Chinese Academy of Sciences' Institute of Vertebrate Paleontology and Paleoanthropology.This undated image shows a restoration drawing of the "Chicago Archaeopteryx" based on a specimen collected by the Field Museum of Natural History in Chicago, the United States. (Chinese Academy of Sciences/Handout via Xinhua)In addition to skeletal features, the study also uncovered preserved soft tissues. Notably, the shape of the toe pads closely resembles that of modern ground-foraging birds, indicating this creature likely had remarkable walking abilities."These findings support the idea that the creature may have enjoyed a versatile lifestyle, moving between the ground and possibly trees, indicating greater flexibility than previously thought," Hu said.The Chicago specimen is also the first Archaeopteryx specimen found to have "tertials" -- the third row of feathers on a bird's wing, which are thought to enhance flight efficiency. Since such structures have never been observed in non-avian feathered dinosaurs, their presence in Archaeopteryx suggests that they could represent a novel flight-related feature, which would have been an important evolutionary step toward the development of flight, according to the study.One of the world's most famous fossil species, Archaeopteryx was discovered shortly after the publication of Darwin's "On the Origin of Species," offering strong support for the theory of evolution. However, the "original bird" has puzzled scientists for about 160 years since, with discussions revolving around whether it was a dinosaur or a bird.The study of the Chicago specimen has offered new evidence of the enigmatic creature, and shows great potential for the use of advanced technologies in the future analysis of fossil bird skulls, the researchers said.