Our earliest ancestors may have breathed through their ears, say paleontologists Martin Brazeau and Per Ahlberg of Uppsala University in Sweden. The tubes that form the middle-ear canal in humans probably evolved from a pair of gill-like holes that allowed primeval sea creatures to breathe from the back of their heads, the researchers find.
Brazeau and Ahlberg deduced this transformation from studies of the 370-million-year-old Panderichthys, an intermediate species between fish and the first four-limbed animals to crawl onto land. Panderichthys had small bones in its skull that appear to be early analogues of both ear canals and the gill system in some modern fish. Brazeau theorizes that the canals developed into true ears only after Panderichthys's descendants became air breathers, freeing up the former gill structures for sensory functions.
"We have long suspected that there was a connection between throat structures used for air breathing and middle-ear structures used for hearing," says Jennifer Clack of the University Museum of Zoology in Cambridge, England, who has studied related fossils. "Here is the concrete evidence."
