The theory that birds descended from dinosaurs is now widely accepted. This transition is also understood to encompass some of the most dramatic morphological, functional, and ecological transformations that eventually gave rise to the characteristic body structure of birds.
However, paleontologists are still scratching their heads to understand how this fantastic evolutionary event happened, which is why the latest discovery of Chinese Academy of Sciences: a Cratonavis zhui.
Is about a complete new fossil bird which was found in the Asian country, 120 million years old, which, Chinese experts say, further complicates this problem by displaying an articulated dinosaur-like skull with a bird-like body.
In addition, the experts, through a statement, detailed that this fossil specimen it retains a strikingly elongated scapula and first metatarsal, making it stand out among all other birds, including fossil ones.
The study, published in Nature Ecology & Evolution on January 2, was conducted by paleontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences.
Cratonavis is positioned between the more reptile-like long-tailed Archeopteryx and Ornithotoraces (which had already evolved many modern bird traits) on the avian evolutionary tree.
The scientists said that to study the fossil skull they first used a high-resolution computed tomography (CT) scan. They then digitally extracted the bones from their rocky tomb and reconstructed the skull’s original form and function.
The result shows that Cratonavis’s skull is morphologically nearly identical to that of dinosaurs such as Tyrannosaurus rex rather than being bird-like. “Primitive cranial features speak to the fact that most Cretaceous birds, such as Cratonavis, could not move their upper beak independently with respect to the braincase and lower jaw, a widely distributed functional innovation among living birds. that contributes to its enormous ecological diversity,” said dr. Li Zhiheng, lead author of the study.
Regarding the foreign scapula and metatarsal in Cratonavis, Dr. Wang Min, lead and corresponding author of this study explained that the scapula is functionally vital for avian flight and conveys stability and flexibility.
“We trace changes of the scapula through the Theropod-Bird transition, and postulate that the elongated scapula might increase the muscle’s mechanical advantage for humerus retraction/rotation, compensating for the overall underdeveloped flight apparatus in this primitive bird. , and these differences represent morphological experimentation in early flight behavior in the diversifying bird.”
According to the experts in their report, the new study shows that the first metatarsal was subject to selection during the dinosaur-bird transition that favored a shorter bone. It then lost its evolutionary change once it reached its optimal size, less than a quarter of the length of the second metatarsal.
“However, there was greater evolutionary lability between Mesozoic birds and their dinosaur relatives, which may have resulted from conflicting claims associated with their direct employment of the hallux for locomotion and feeding,” said co-author Dr. Thomas Stidham. . For Cratonavis, such an elongated hallux probably derives from selection for raptorial behaviour.
The aberrant morphologies of the scapula and metatarsals preserved in Cratonavis highlight the breadth of skeletal plasticity in early birds, said Dr Zhonghe Zhou, co-author. Changes in these elements along the theropod tree show evolutionary branch-specific change resulting from the interplay between development, natural selection, and ecological chance.