Chinanews.com, Beijing, December 12 (Reporter Sun Zifa) Is the hollow skeletal structure of pterosaurs just to reduce weight and adapt to flight? Is the relatively thick bone wall a "unique skill" of the Dzungar pterosaurs? ......
The team of Wang Xiaolin and Jiang Shunxing from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences conducted in-depth research on the pterosaur fossil materials collected from the strata of the Rehe biota in China about 1 million years ago, and recently discovered and established a new genus and species of pterosaur - "North China Kraton Pterodactyl".
A fossil specimen of a new genus and species of pterosaurs, "North China Craton", found in strata of the Rehe biota in China about 1 million years ago. Photo by Chinanews reporter Sun Zifa
This important pterosaur research paper was recently published in Heliyon, a subsidiary of the internationally renowned academic journal Cell. Associate researcher Jiang Shunxing, the first author and co-corresponding author of the paper, said in an interview with reporters that the Rehe biota is divided into three stages: early, middle and late, for a long time, pterosaur fossils were only found in the middle and late stages, and the first pterosaur fossil was not found until 2022 in the early stage, but only one wing and right foot were preserved, and the researchers classified it as a bird's palm pterosaur. The North China cratonic pterosaur in this study is the second early pterosaur specimen of the Rehe biota, and although it is not complete, it has preserved part of the axial skeleton and most of the right wing.
Jiang Shunxing, the first author and co-corresponding author of the paper and associate researcher of the Institute of Paleovertebrology of the Chinese Academy of Sciences, introduced the fossil discovery and research results of the new genus and species of pterosaurs, "North China cratonic pterosaur". Photo by Chinanews reporter Sun Zifa
With a wingspan of about 1.8 meters, the North China craton pterosaur is a member of the ancient pterosaur class of medium size, with a large nerve foramen on the ventral surface of the proximal end of the first wing phalanx, and the joint of the black rostroid and scapula is not enlarged, and has a combination of five characteristics: first, a nearly square sternal plate; second, the articular surface of the coracoid bone associated with the sternum is concave, and it has a posterior expansion; third, the proximal humeral head and deltoid crest lack protrusions; fourth, the humerus is slightly longer than the pterygometacarpus; Fifth, the phalanges of the first and third wings are nearly equal in length.
Based on these characteristics, the research team identified a new genus and species of Pterodactylidae. In addition to the pterosaur, this fossil specimen also contains three representative creatures of the Rehe biota, including the wolf-fin fish, the oriental leaf limb, and the three-tailed mayfly.
The fossil orthotype specimen of "North China Kratonosaurus" discovered in this study. Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
Jiang Shunxing pointed out that for a long time, as flying reptiles, pterosaurs had a thin-walled, hollow skeletal structure like birds, which has been considered an adaptation to flight behavior, most often explained as the need to lose weight when flying. In addition, in the pterosaur taxa, Dzungar pterosaurs are traditionally considered to be a type with particularly thickened bone wall, which is also one of its identification characteristics, and some researchers have believed that the thickening of the bone wall of Dzungar pterosaurs is an adaptive feature of frequent takeoff.
The North China craton pterosaur in this study did not belong to the Junggar pterosaur class, but had a large relative bone wall thickness, which made the research team doubt the above traditional view, so a total of 143 sets of data were obtained by synthesizing the published data on the relative thickness of the bone wall of the pterosaur and supplementing a large number of information on Junggar pterosaurs and other Chinese pterosaur fossils.
Jiang Shunxing said that through statistical analysis of these data, the research team found that the relatively thick bone wall of pterosaurs was not unique to Junggar pterosaurs, but was widely distributed in the Jurassic flourishing "beak-billed dragons" (non-pterosaurs) and some relatively early pterosaurs, and also had similar characteristics of relatively large bone walls in several known pterosaurs, so the relatively thick bone wall should be a primitive feature of pterosaurs.
In fact, in addition to the different relative thickness of the bone wall of different pterosaur species, there are many other factors that will also affect the relative thickness of the bone wall, including obvious thickness differences in different parts of the same bone, and the relative thickness of the same part of the same bone will also change during the growth and development from juvenile to adult.
Tissue section of the diaphylanx of the second wing of the "North China Kraton" shows its relatively thick bone wall and incomplete growth arrest line. Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
In addition, different bones in the same body of pterosaurs will also have large variations in bone wall thickness. This study found that not only the relatively thick bone wall could not be used as a characteristic for the identification of Dzungar pterosaurs, but also the bone walls of Dzungar pterosaurs were not all thick, such as the relatively thin bone walls of the humerus and radius, which also existed in living vertebrate bats. From the analysis of material mechanical properties, the thinner the thickness of a hollow homogeneous tube, the stronger the torsion resistance.
"Therefore, it is likely that the relative thinning of the humeral and radius bone walls of Dzungar pterosaurs is similar to the adaptation of bats to flight, increasing the torsional resistance of their bones during drum-wing flight, rather than just for weight loss." Jiang Shunxing said.
Statistical histogram of the relative thickness of the bone wall of the pterosaur taxa. Courtesy of the Institute of Paleospine, Chinese Academy of Sciences
Prof. Wang Xiaolin, co-corresponding author of the paper, emphasized that although the research team's latest research on the North China craton pterosaur and Junggar pterosaur has challenged and given a new explanation for the long-held traditional view that the bone wall of pterosaurs thinned only to reduce weight, there is no doubt that the bones of extinct pterosaurs and living bats, birds and other flying animals have evolved to a thin bone wall and hollow structure, and the general direction is to reduce weight and adapt to flight. (ENDS)