Human Ear Evolution Study Suggests Middle Structure Developed from Prehistoric Fish Gill

A fossilized Shuyu fish braincase was found by scientists. The team was able to recreate seven virtual casts of the Shuyu brain despite the specimen skull only being the size of an average fingernail.

They also discovered the first armored galeaspid fossil, which dates to 419 million years ago and is entirely preserved with gill filaments.

The Spiracle

The team from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences discovered the spiracle, slits that some species use to breathe. They are located behind the eyes and lead to the mouth.

The spiracle is in charge of ingesting water in sharks and all other rays before it is expelled from the gills.

The hearing canal used to transmit sound to the brain via tiny inner ear bones eventually developed from the spiracle into the ear of contemporary four-legged vertebrates.

This function has persisted throughout human evolution, and the information gained from the two fossils completes the picture showing how the human ear evolved from fish gills.

Three tiny, vibrating bones located in the human middle ear are essential for moving sound vibrations into the inner ear, where they are converted into nerve impulses that allow us to hear.

According to the study's first author, Professor Zhikun Gai of IVPP, these fossils offered the first anatomical and prehistoric proof of a vertebrate spiracle descended from fish gills.

For the study, a total of seven virtual endocasts of the Shuyu braincase were rebuilt.

The Missing Links

The fingernail-sized skull of Shuyu revealed almost all of its cranial anatomy, including its five distinct brain regions, sensory organs, and cranial nerve and blood vessel passages.

The "missing links" from the gill to the middle ear were hailed as fossils discovered in Changxing, China, in the Zhejiang Province, and Qujing, China, in the Yunnan Province.

Professor Min Zhu, an academician of the Chinese Academy of Sciences, said that the origins of numerous vital human body parts, including the teeth, jaws, middle ears, and other parts, can be traced back to fish.

The main objective of paleontologists, he continued, is to uncover the crucial gaps in the evolutionary process that led from fish to humans.

Shuyu has been viewed as a crucial missing piece that is just as significant as Archaeopteryx, Newsweek reports.

Professor Per Ahlberg from Uppsala University and an academician of the Royal Swedish Academy of Sciences who collaborated on the research said that their discovery ties together recent discoveries of the spiracles of the earliest jawed vertebrates, the middle ears of the first tetrapods, the gill pouches of fossil jawless vertebrates, and other parts of the spiracular slit's history to tell this extraordinary evolutionary tale.

The group of scientists are composed of Zhikun Gai, Min Zhu, Per E. Ahlberg, and Philip C. J. Donoghue. Their research was recently published in the website of Frontiers of Ecology and Evolution.