Li's source predator micro-tomography reconstruction map Mao Fangyuan / Courtesy of the picture
Li's source predator ecological environment and Reconstruction of Lujiatun fauna Zhao Chuang/Painting
This is a special "breakup" from 124 million years ago, the protagonist is one of the organs that manage "listening" and the other is the organ that manages "chewing".
Yes, a long time ago, the organ responsible for "hearing" and "chewing" was one. Mao Fangyuan, Wang Yuanqing and other scholars from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences collaborated with Meng Jin of the American Museum of Natural History to discover the li's source predator fossils 124 million years ago: once integrated hearing and chewing organs, in order to adapt to natural selection and improve the efficiency of hearing and chewing, the two modules were gradually separated.
Not long ago, the international academic journal Science published a paper on this achievement. It is mentioned that this 124 million-year-old fossil perfectly shows the two modules of hearing and chewing organs, and the phenotypic characteristics of the isolated nodes are evolved in the basal mammals, and the isolated hearing and chewing organs make the mammals' hearing more sensitive and chewing more efficient.
According to Mao Fangyuan, the first author of the paper and an associate researcher at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, modular evolution is a concept that combines evolutionary biology and developmental biology. Organisms can be decomposed at different levels into small morphological, developmental or functional units, which are relatively independent in development and gene regulation, have different rates of variation in evolution, and can independently accept the role of natural selection without affecting the morphological functions of other modules.
The forelimbs of vertebrates, an example of homologous modular evolution, can evolve into wings, fins, or human hands, but do not affect other parts, such as the morphology and function of the hind limbs.
Looking at the protagonist of this scientific discovery, based on 6 specimens preserved in three dimensions in the Lujiatun layer of the early Cretaceous River biota, the researchers used microscopic tomography and three-dimensional reconstruction to establish a new genus of paradonts: Li's source predator. Mao Fangyuan said, "The name was taken in honor of one of the authors of the article, li Chuankui, one of the founders of early Chinese mammal research who died in October this year." ”
Studies have shown that during the bite and chewing process, the jaw of the Lee's source predator has lateral movement and rotation along the long axis in addition to the opening and closing movement. This multi-directional process of jaw chewing is likely to be one of the selective pressures that cause the middle ear auditory bone of the mammal to detach from the tooth bone and the Myrdochondrine.
Mao Fangyuan said that in the past 20 years, among the Mesozoic mammals found in western Liaoning in China, the ossified Mai's cartilage of reptiles and other ossiculatory bones of Liaoning ceralates provide evidence of the evolutionary transition pattern from the middle ear of the mandibular to the middle ear of a typical mammal. However, in the transitional middle ear, the auditory bone, although detached from the dental bone, is still tightly twisted with the ossified Mychonne cartilage, which is connected to the dental bone; therefore, the functions of hearing and chewing have not been completely separated and have influenced each other.
The appearance of multiple fossil specimens of the Lee's source predator now shows for the first time a key feature, that is, the absence of a bone-free link between the auditory bone and the Mai's cartilage, representing a key node in the separation of the auditory and chewing modules in mammalian evolution.
Mao Fangyuan told reporters that a series of complete and continuous fossil evidence also shows that the isolated hearing and chewing modules have enhanced their "each doing their part" evolutionary ability, the auditory organs have the potential to develop to high-sensitivity and high-frequency hearing, and the chewing organs have also obtained the possibility of diversifying the evolution of teeth and occlusal patterns to ingest different foods, resulting in the flourishing of live mammals.
According to her, thanks to the results of high-precision microscopic tomography, the Lee's source predator fossil study also revealed that in the early days — at least 120 million years ago — there were 5 middle ear ossicles, only 5 mm long, and for the first time, 5 specific three-dimensional forms of ossicles were obtained. Today, mammals have only 3 middle ear ossicles, the other two ossicles, one that evolved into an external tympanic bone attached to the listening membrane, and the other that has been lost or fused into the articulation of the auditory chain during evolution.
It is worth mentioning that as an important part of the auditory organs, the middle ear receives signals, the inner ear transmits signals to the brain, and now this fossil study of Lee's source predator also found that the inner ear, which is closely related to the auditory bone of the middle ear, has been extended in a straight line to the base of the skull, but has reached its limit, representing an evolutionary "trial and error experiment" in which the mammalian cochlea grows in different ways to improve hearing.
"A number of research results of Lee's source predator fossils have provided more reference evidence for developmental biology research." Mao Fangyuan said that the success of mammals in earth's ecosystem today is inseparable from the various successful and failed evolutionary experiments of their ancestors. The separation of the auditory and chewing modules is an example of this evolutionary success.
China Youth Daily, China Youth Network reporter Qiu Chenhui Source: China Youth Daily