A lot of living birds have what is called a kinetic skull. Yuanchuavis reveals a mosaic of dinosaurian and bird characteristics such as a feathered bird body with wings, a toothed mouth, and an immovable dinosaurian palate and snout.
These functions ruled out any kinesis in the skull of early birds, the paleontological team was able to reveal a secret hidden in the fossil skull regarding the origin of kinesis. Dinosaurs and the oldest bird Archaeopteryx have that contact, which helps stabilize the palate bones and restricts motion. In contrast, the palatine of living birds, like Yuanchuavis, does not have that contact, thus facilitating back-and-forth moving throughout bird skull kinesis.
Many living birds have what is termed a kinetic skull. This means that upper beak motion is independent of the braincase. This movement is accomplished by two chains of skull bones lined up from the back of the skull to the front, with one chain along the cheek and the other along the palate (roofing system of the mouth). These chains of interconnected bones help to transfer forces from the back of the skull to the beak, enabling its motion.
Contrast of skull morphology of dinosaurs, Yuanchuavis, and modern birds, showing that essential components of the two chains of skull bones crucial for cranial kinesis are doing not have in Yuanchuavis and dinosaurs. Credit: Wang Min
” We still do not understand which chain of bones was finished and freed initially in bird development, and even if it was all finished together,” stated Professor Wang Min from IVPP, lead and matching author of the study. “What we see in dinosaurs and the earliest birds like the enantiornithine Yuanchuavis is that these chains are missing connections or are locked in location since they linked to more bones that would stop most movements.”
” This fossil actually helps to narrow the time when, and where on the bird family tree, components of that portable beak or kinesis evolved. We can show that it absolutely was not provide any earlier in bird evolution,” said Professor Thomas Stidham from IVPP, coauthor of the study.
Yuanchuavis is a member of a group of extinct birds called enantiornithines or “opposite birds”– so named due to the fact that of key differences in their skeleton from living birds. The enantiornithines ended up being extinct at the end of the Cretaceous during the worldwide mass termination marking the end of the Age of Dinosaurs.
Digital reconstruction of the skull of the Cretaceous bird Yuanchuavis kompsosoura. Credit: Wang Min
By using high-resolution CT-scanning, the research study group had the ability to digitally recognize, isolate, and assemble all skull bones into a detailed three-dimensional restoration. This work exposed lots of physiological details not understood for early risers. Yuanchuavis reveals a mosaic of dinosaurian and bird qualities such as a feathered bird body with wings, a toothed mouth, and an immovable dinosaurian palate and snout.
Amongst the primitive dinosaurian functions of Yuanchuavis is the existence of bar-forming contacts among the bones of the temporal region of the skull behind the eye that are found in dinosaurs, snakes, crocodiles, and lizards (referred to as the diapsid condition). These interconnections essentially “lock up” one of the chains of bones in Yuanchuavis that is otherwise totally free in living birds, a requirement for kinesis.
The scientists comprehensive research study of the shape of the pterygoid, a palate bone, reveals that it had no direct contact with another bone called the quadrate, which is also needed to finish the palatal chain of bones in kinesis. That lack of contact is seen in most dinosaurs, including Triceratops and Tyrannosaurus, however the bones get in touch with one another in living birds.
In addition, the research team was able to verify that the pterygoid of enantiornithines retained an unique shape. It had a two-pronged projection behind the eye like Velociraptors and other close dinosaurian family members of birds.
The research studys group validated that the pterygoid of enantiornithines maintained a distinct shape. It featured a two-pronged protrusion behind the eye, comparable to Velociraptors and other dinosaurs carefully associated to birds.
These functions ruled out any kinesis in the skull of early birds, the paleontological group was able to uncover a secret concealed in the fossil skull relating to the origin of kinesis. Detailed analysis and contrast of the palatine, another bone in the taste buds of Yuanchuavis, reveals that the palatine does not have a crucial contact with the jugal bone, a part of the cheekbone. Dinosaurs and the earliest bird Archaeopteryx have that contact, which assists stabilize the taste buds bones and restricts movement. In contrast, the palatine of living birds, like Yuanchuavis, does not have that contact, hence facilitating back-and-forth moving during bird skull kinesis.
According to Professor Wang, the modification in palatine bone shape from having contact with four to just 3 other skull bones in enantiornithines may be where skull kinesis began.
” New features evolve from old ones, and kinesis must have evolved in birds from a forefather lacking it,” stated Professor Wang.
Professor Stidham observed that most individuals would anticipate early birds to have bird skulls that matched their feathered wings and bodies. “However, these early birds hadnt entirely moved beyond their dinosaurian ancestry, and the evolutionary course from a little feathered dinosaur to a living bird was not a straight line,” he said, keeping in mind that bird evolution had its “detours and dead-ends.”
Reference: “Insight into the evolutionary assemblage of cranial kinesis from a Cretaceous bird” by Min Wang, Thomas A Stidham, Jingmai K OConnor and Zhonghe Zhou, 5 December 2022, eLife.DOI: 10.7554/ eLife.81337.
Digital reconstruction of the skull of the Cretaceous bird Yuanchuavis kompsosoura. Credit: Wang Min
A brand-new study from researchers at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the Field Museum of Natural History has found that birds retained essential dinosaurian characteristics for millions of years after the split in between dinosaurs and birds.
The study, which analyzed and reconstructed a 120-million-year-old bird fossil called Yuanchuavis kompsosoura, found that this ancient bird maintained many of the same functions as its dinosaurian ancestors. This fossil likewise offered insights into the origins of cranial kinesis, a crucial feature in the skulls of modern birds.
The study was just recently published in the journal eLife.
