The human middle ear evolved from fish gills, according to a study of a 438-million-year-old fossil fish brain.
Scientists discovered the fossil of the skull of a Shuyu fish. Although the skull was only the size of a fingernail, they were able to reconstruct seven virtual casts of the brain.
They also discovered the first 419-million-year-old armored galeaspid fossil preserved entirely with gill filaments.
The team from the Chinese Academy of Sciences’ Institute of Vertebrate Palaeontology and Paleoanthropology (IVPP) found the spiracle, slits behind the eyes that lead to the mouth and allow some species to breathe.
In sharks and all rays, the spiracle is responsible for taking in water before expelling it from the gills.
The stigma evolved into the ear of modern four-legged vertebrates and eventually became the ear canal, used to transmit sound to the brain via tiny inner ear bones.
This function has been preserved in the course of evolution up to humans.
The detail derived from the two fossils is the final piece of the puzzle, proving the lineage from fish gills to the human ear.
The human middle ear houses three tiny, vibrating bones that are key to transporting sound vibrations into the inner ear, where they become nerve impulses that allow us to hear.
Professor Zhikun Gai of the IVPP and lead author of the study said: “These fossils provided the first anatomical and fossil evidence for a vertebrate spiracle derived from fish gills.”
A total of seven virtual endocasts of the Shuyu brain bowl were reconstructed.
Almost all of the details of Shuyu’s skull anatomy were revealed in his fingernail-sized skull, including five brain divisions, sensory organs, and cranial nerve and blood vessel passages.
The fossils, found in China’s Changxing, Zhejiang Province and Qujing, Yunnan Province, have been hailed as “missing links” from the gill to the middle ear.
Professor Min Zhu, Academician of the Chinese Academy of Sciences, added: “Many important human structures can be traced back to our fish ancestors, such as our teeth, jaws, middle ears, etc.
“The main task of paleontologists is to find the important missing links in the evolutionary chain from fish to humans.
“Shuyu was seen as a key missing link, as important as Archeopteryx.”
Professor Per Ahlberg of Uppsala University and an academic at the Royal Swedish Academy of Sciences who collaborated on the research said: “Our find bridges the entire history of the spiral slit and brings together recent discoveries from the gill pouches of fossil jawless vertebrates from the spiracles of the earliest vertebrates with jaws extending to the middle ears of the first tetrapods, telling this extraordinary evolutionary story.”
The study was published in the journal Frontiers in ecology and evolution.
This story was provided to Newsweek by Zenger News.