Few people notice their middle ear – unless it’s inflamed. But it’s the little guy that hides in his ear, both for humans and for the hearing of other mammals. Therefore, its evolutionary mechanism has become a major research topic for palaeontologists in the past many years.
Hot River Jun beast type specimen (bottom right corner) and a north ticket specimen preserved in the same rock plate Wang sea ice / supplies map
Hot River Jun beast ecological restoration map Xu Yong / supplies
Now, wang Haibing, assistant researcher at the Institute of Paleovertebrates and Paleoanthropology of the Chinese Academy of Sciences, Wang Yuanqing, a researcher at the American Museum of Natural History, has proposed a new model of mammalian middle ear evolution: special jaw joints and their feeding patterns, or can accelerate the evolution of the middle ear, simply by way.” To some extent, eating can promote hearing.”
All this, but also from a “specimen body about 15 cm long” fossil.
The fossil was found in the Baibai-tong-nine Buddha Church group under the Lingyuan Open-seigou in Liaoning Province, and was kept on the same rock slab as a fossil of the Northern Ticket, about 120 million years ago.
Wang Haibing is the youngest researcher in the research team, is also the first author of the paper, according to him, after a long period of careful indoor repair, data processing and comparative research, the research team determined that the fossil represents a new species of multi-tumor toothed beast, named it “Gai’s hot river beast” – It is also the first time scientists have found fossils of multi-tumor-toothed animals from the Jiufu Church group.
“The most interesting part of this specimen is that its skull has a very complete middle ear structure. Wang Said.
The evolution of the middle ear in mammals is considered a classic example of the biological re-enactment law, so scientists are “very sensitive” to its emergence. The mammalian middle ear went through three stages of evolution from the middle ear of the lower jaw, the transitional middle ear, to the middle ear of a typical mammal, Wang said. However, the time and mechanism of the occurrence of different middle ear evolution stages in the mammalian branches is always a difficult point of study.
Prior to this, “brain swelling” and “negative heterorate growth” are two common hypotheses of the evolutionary mechanism of the middle ear in mammals, the former of which holds that the enlargement of the brain skull during mammalian growth leads to the later movement of the middle ear position and eventually disengage disjointed from the jaw, while the latter emphasizes that in the early stages of embryonic development, the middle ear-shaped bone is larger relative to the lower jaw. The middle ear bone is osteoblastized earlier, so in the late stage of embryonic development, with the enlargement of the skull and jaw, the middle ear bone eventually disengages from the jaw.
However, with advances in fossil research and embryo development in emerging animals, support for both hypotheses is waning.
It was not until the emergence of the “Gai” fossil that scientists saw a new dawn.
“The positive specimen of the Gei’s hot river beast preserved a complete middle ear structure and provided direct evidence for the study of the evolution of the ear region of early mammals. Wang Said.
Specifically, the work reveals the complete shape of the individual bone blocks in the middle ear of the polymamal-toothed animal, as well as the relationship between each other, complementing the “extremely weighty puzzle” for the evolution of the cerebral bone in mammalian syltos, from the middle ear of the jaw to the middle ear of a typical mammal.
Based on this study, researchers, including Wang Haibing, have a clearer understanding of the evolution of the upper tibin in mammals. The study revealed for the first time that the upper tib in early mammals changed from a separate bone to a state of gradual healing with the hammer bone, becoming the outer part of the hammer bone.
At the same time, the researchers also proposed a new model of middle ear evolution in early mammals through morphological evidence and systematic developmental analysis.
In mesozoic mammals, the isozoic synobs evolved typical mammalian middle ears at least 160 million years ago in the Mid/Late Jurassic, while during the same period, and later in the Early Cretaceous, all other known mammalian groups retained the transitional middle ear.
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Wang Haibing found the explanation is: Gai’s hot river beast belongs to the hetero-beast, in the hetero-beast, the skull and jaw joint is a more open pattern, this structure allows its jaw to have a large forward and back range of activity, resulting in its feeding method is very unique, it is likely to provide a very strong choice of the middle ear evolution pressure, This leads to the acceleration of the evolution of the middle ear of the heteros.
“It is also understood to be ‘eating promotes hearing’. Wang Said.
Of course, there is also a transitional middle ear evolution phase, but according to Wang Haibing, this phase lasts longer in the isofauna, shorter than all other mammals, probably because of its unique jaw jointand and feeding method, They acquired the shape of the typical mammalian middle ear at least 160 million years ago, ahead of all other mammalian groups.
The results were published online in nature, an internationally renowned academic journal. It records Wang Yuanqing and Wang Haibing’s team based on the results of systematic development altogether, and the specific discussion of the mechanism of middle ear evolution in mammals, which will also become a new hypothesis from the date of publication of the paper.