419-Million-Year-Old Chinese Fossil Shows Human Middle Ear Evolved From Fish Gills - SciTechDaily

Embryonic and fossil evidence proves that the human middle ear evolved from the spiracle of fishes.

However, the origin of the vertebrate spiracle has long been an unsolved mystery in vertebrate evolution.

“These fossils provided the first anatomical and fossil evidence for a vertebrate spiracle originating from fish gills.” — Prof.

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

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

GAI Zhikun from IVPP, first author of the study, researchers from the institute successively found over the last 20 years a 438-million-year-old Shuyu 3D braincase fossil and the first 419-million-year-old galeaspid fossil completely preserved with gill filaments in the first branchial chamber.

“These fossils provided the first anatomical and fossil evidence for a vertebrate spiracle originating from fish gills,” said GAI.

However, fish spiracles were eventually replaced in most non-fish species as they evolved to breathe through their noses and mouths.

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.

“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.

Donoghue, 19 May 2022, Frontiers in Ecology and Evolution.

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