419-million-year-old Chinese fossil shows human middle ear evolved from fish gills

3D Shuyu puzzle. Credit: IVPP

The human middle ear, home to three small, vibrating bones, is essential for transmitting sound vibrations to the inner ear, where they become nerve impulses that allow us to hear.

Embryonic and fossil evidence proves that the human middle ear originated from the miracle fish. However, the origin of vertebrate stigma has long been an unsolved mystery in vertebrate evolution.

“These fossils provided the first anatomical and fossil evidence of a vertebrate horizontal miracle of fish gills.” – Professor GAI Zhikun

about twentye Horn researchers, believing that early vertebrates should possess a complete spiny gill, looked for one between the mandibular and hyoid arches of early vertebrates. Despite extensive research spanning over a century, none have been found in vertebrate fossils.

Now, however, scientists from the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) and their collaborators have found evidence of this mystery in armored galeaspidae fossils in China.

Their findings were published in the journal Frontiers in Ecology and Evolution May 19, 2022.

According to Professor GAI Zhikun of IVPP, first author of the study, researchers at the institute have consecutively discovered the 438 million-year-old creature over the past 20 years. Shuyu 3D puzzle and first fully preserved 419 million year old fossil with gill filaments in the first gill chamber. The fossils were found in Changxing, Zhejiang Province, and Qujing, Yunnan Province, respectively.

Shuyu 3D Virtual Reconstruction

Shuyu’s 3D virtual reconstruction. Credit: IVPP

“These fossils provided the first anatomical and fossil evidence of a vertebrate horizontal prodigy from fish gills,” GAI said.

A total of seven hypothetical endings of Shuyu Then the puzzles were pieced together. Almost every detail of skull anatomy Shuyu It was revealed in his fingernail-sized skull, comprising five brain sections, sensory organs, cranial nerve pathways, and cranial blood vessels.

“Many structures important to humans can be traced back to our fish ancestors, such as our teeth, jaws, middle ears, etc. The main task of paleontologists is to find important missing links in the evolutionary chain from fish to man. Shuyu He was considered a missing link no less important than ArcheopteryxAnd the Ichthyostega And the Tiktaaliksaid ZHU Min, an academician of the Chinese Academy of Sciences.

A fully preserved 419-million-year-old gallepid fossil with gill filaments

The earliest fossil of a 419 million year old gallipid with gill filaments in the first gill chamber. Credit: IVPP

The miracle is a small hole behind each eye that opens in the mouth of some fish. In sharks and all rays, the miracle is responsible for introducing water into the mouth space before it is expelled from the gills. The miracle is often located on top of the animal allowing it to breathe even when the animal is mostly buried under sediment.

in the multi-winged, which are the most primitive living bony fishes, use vents to breathe air. However, fish breathing openings were eventually replaced in most non-fish species as they evolved to breathe through their noses and mouths. First of all[{” attribute=””>tetrapods, the spiracle seems to have developed first into the Otic notch. Like the spiracle, it was used in respiration and was incapable of sensing sound. Later the spiracle evolved into the ear of modern tetrapods, eventually becoming the hearing canal used for transmitting sound to the brain via tiny inner ear bones. This function has remained throughout the evolution to humans.

“Our finding bridges the entire history of the spiracular slit, bringing together recent discoveries from the gill pouches of fossil jawless vertebrates, via the spiracles of the earliest jawed vertebrates, to the middle ears of the first tetrapods, which tells this extraordinary evolutionary story,” said Prof. Per E. Ahlberg from Uppsala University and academician of the Royal Swedish Academy of Sciences.

Reference: “The Evolution of the Spiracular Region From Jawless Fishes to Tetrapods” by Zhikun Gai, Min Zhu, Per E. Ahlberg and Philip C. J. Donoghue, 19 May 2022, Frontiers in Ecology and Evolution.
DOI: 10.3389/fevo.2022.887172

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