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Ancient fish reveals one step in how ears evolved

30 January 2006

The skull bones of an ancient fish have revealed the early stages of how our ears evolved.

Structures corresponding to those most likely used for breathing in the fish show the early stages of evolving into the structures in our ears.

Martin Brazeau and Per Ahlberg, palaeontologists at Uppsala University in Sweden, studied the fossil of a Panderichthys , an extinct metre-long fish that existed in the Devonian period 370 million years ago.

Comparisons

They compared structures in its skull with those of a more primitive fish and an early tetrapod - a group of ancient four-legged vertebrates that were the primitive ancestors of amphibians, reptiles, birds and mammals.

Fish and tetrapod link

The team found the Panderichthys structures hadfeatures found in both fish and tetrapods. The findings support the idea that Panderichthys is an evolutionary link between fish and the early tetrapods.

Breathing holes

Paired spaces, linking the back of the mouth to the outside of the animal, are far larger than expected for a normal fish. The team say that these spaces would have been filled with a spiracle - a special opening and pathway that was used to draw water over the gills like breathing holes in modern-day sharks and rays.

Evolutionary transition

Over time this spiracular space was used to create the middle ear we see in some early tetrapods. One bone next to the spiracle evolved to have a totally different function, as a bone that transmitted sound. The discovery shows a small part of the evolutionary transition between the two functions of this part of the animal.

The research is published in the journal Nature

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