A three-dimensional reconstruction of the skull of the bird’s Ray-tailed Quail 120 million years ago. Photo courtesy of Wang Min
Birds are currently the most diverse terrestrial vertebrates in the world. Why did they evolve so successfully? A key factor is that some of the bones of the bird’s skull can move independently of each other, which helps the beak complete a large number of fine movements, such as pecking at food of different sizes and forms, nesting and so on. In a sense, a bird’s beak is no less flexible than the hands of other vertebrates.
Recently, the nature index journal eLife published a result of the team of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (hereinafter referred to as the Institute of Vertebrate Paleontology), in which researchers revealed the characteristics of early bird skull evolution through high-precision three-dimensional scanning and reconstruction.
Wang Min, the corresponding author of the paper and a researcher at the Institute of Paleovertebrae, introduced that the unique mobility of bird skulls mainly depends on the flexion band distributed in the snout and two skeletal channels, one is a “lateral channel” formed by square bones-square cheekbones-cheekbones-maxilla, and the other is a “palatine channel” composed of square bones-wing bones-palatine bones-vomer bones on the palatine surface.
“Simply put, as the square bones rotate forward and backward, the bones on these two channels are displaced through movable joints, like a conveyor belt, completing the opening and closing of the mouth. In the ancestor of birds, non-avian dinosaurs, its thick skull is very clumsy because it lacks the mobility of these two channels. ”
However, due to the long-term limitations of fossil preservation and research methods, paleontologists do not know the morphological function of the main areas of the skull, especially how these two pathways have changed in the evolutionary history of birds.
Therefore, the research team of the Paleovertebrate Institute used high-precision CT to restore the skull of the Mesozoic anti-bird Ya-tailed quail they had previously discovered, and reconstructed the three-dimensional morphology of almost all the skull skeletons, including the bones that make up the skull mobility channel.
The researchers found that the quail retained the temporal structure typical of the archosaur bitemporal arch, which restricted the anteroposterior movement of the zygomatic bones, meaning that its “lateral channels” were not formed; When they restored the morphology of the palatal surface skeleton, they also found that the palatal surface structure of the quail was similar to that of theropods, relatively primitive, and the “palatal channel” did not appear.
Interestingly, compared to the evolutionarily conserved structure of the temporal and palatine regions, other skull morphologies of quails exhibit typical and progressive bird characteristics.
“This shows that the rate of evolution of different parts of the skull of birds is not uniform.” Wang Min explained that this primitive and progressive morphological feature appears at the same time, which is a typical mosaic evolution.
Anti-birds represented by quails retain primitive non-movable skulls, but they are one of the most successful taxa in the evolution of Mesozoic birds because they spread across the globe. But by the end of the Cretaceous mass extinction event, they were “wiped out”, while the present-day bird-type with movable skulls survived and rapidly evolved in the Cenozoic era to form all modern birds. “This also shows that the mobility of bird skulls increases the adaptability of individuals in the face of extreme selection pressures.” Wang Min said. (Source: Hu Minqi, China Science News)
Related paper information: https://doi.org/10.7554/eLife.81337