A new fossil from China has left scientists amazed at birds’ evolutionary journey, which are believed to be descendants of dinosaurs. Paleontologists have found a complete 120-million-year-old fossil with a dinosaur-like skull on a body that is built like a bird.
Named Cratonavis Zhui, the fossil has an elongated scapula and first metatarsal, making it stand out from all other birds, including fossil ones. The new find indicates a dramatic transformation morphologically, functionally, and ecologically that gave rise to the characteristic bird body plan.
The new find details have been published in the journal Nature Ecology & Evolution, which states that it highlights a breadth of skeletal plasticity, stemming from their distinct developmental modules and selection for possibly raptorial behaviour. Researchers have noted that the Cretaceous period is a critical time interval that encompasses explosive diversifications of terrestrial vertebrates..
The study of the unique fossil was conducted by paleontologists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences. The team used high-resolution computed tomography (CT)scanning.
They digitally removed the bones from their rocky tomb and reconstructed the original shape and function of the skull. What they saw was that the Cratonavis skull is morphologically nearly identical to that of dinosaurs such as Tyrannosaurus rex rather than being bird-like.
“The primitive cranial features speak to the fact that most Cretaceous birds such as Cratonavis could not move their upper bill independently with respect to the braincase and lower jaw, a functional innovation widely distributed among living birds that contribute to their enormous ecological diversity,” said Dr. LI Zhiheng, a lead author of the study.
Researchers noted that the scapula is functionally vital to avian flight, and it conveys stability and flexibility. trace changes of the scapula across the Theropod-Bird transition, and posit that the elongated scapula could augment the mechanical advantage of muscle for humerus retraction/rotation.
An increased evolutionary lability was present among Mesozoic birds and their dinosaur kins, which may have resulted from conflicting demands associated with its direct employment of the hallux in locomotion and feeding,” Dr. Thomas Stidham, co-author of the paper, said in a statement.
The new study shows that the first metatarsal was subjected to selection during the dinosaur-bird transition that favoured a shorter bone. It then lost its evolutionary lability once it reached its optimal size, less than a quarter of the length of the second metatarsal.
