A fully preserved fossilised skeleton of a bird that lived in what is now China about 120 million years ago, dinosaur-like head perched atop a body that resembles more modern birds, might shed light on important stages in the metamorphosis process. Some of the most extreme changes in habitat, function, and shape occurred during the transition from dinosaur to bird, which ultimately resulted in the basic avian body plan we see today.
Even now, some of those morphological changes can be noticed in how modern birds grow. The exact sequence of these modifications and the nature of the evolutionary pressures that led to the development of purely avian traits are still up for debate.
The intriguing, recently discovered fossil known as Cratonavis zhui may offer crucial insights into the development of contemporary birds. During excavations in northern China, scientists found the body print of Cratonavis, the bird with a dinosaur skull.
In these sedimentary strata, produced about 120 million years ago during the Cretaceous period, body prints of early birds and feathered dinosaurs, notably Confuciusornis sanctus, have been found.
High-resolution computed tomography (CT) scanning was the first step in the scientists' examination of the ancient skull under the direction of palaeontologist Zhou Zhonghe from the Chinese Academy of Sciences (CAS). The team recreated the shape and function of the skull as it was during the bird's life using the digital representations of the calcified bones. The findings demonstrate that the Cratonavis skull is not shaped like a bird, but rather is almost identical to that of dinosaurs like Tyrannosaurus rex.
The remarkable fusion of an akinetic dinosaur head with a bird skeleton supports earlier research on the significance of evolutionary mosaicism in the early diversification of birds. The first metatarsal is thought to have undergone natural selection during the transition from dinosaurs to birds, shortening it in the process, according to the study's authors. Its early roles were eliminated once it reached its ideal size, which was less than a quarter of the length of the second metatarsal.
The elongate scapula may enhance the mechanical advantage of muscle for humerus retraction/rotation, which makes up for this early bird's generally underdeveloped flight apparatus. According to palaeontologist Min Wang, one of the lead authors, these variations represent morphological experimentation in volant behaviour early in bird diversification.
The authors point out that the preserved abnomal morphologies of the scapula and metatarsals from Cratonavis demonstrate the extent of early birds' skeletal plasticity.