Latest research shows that the ‘paratympanic organ’ (PTO) – the innate barometer in the middle ear of birds – evolved from a fish sense organ that detects jaw movement.
The work, published in Nature Communications, sheds new light on the evolutionary trajectory of sensory systems after tetrapods left the oceans and moved onto land.
The ‘spiracular organ’ found in cartilaginous fishes (sharks and rays) and some bony fishes (including gars, sturgeons and lungfishes) is structurally similar to a bird’s PTO and located in the same position within the head, that is, in the wall of the ‘spiracle’ – the first gill slit – from which the middle ear cavity of all land vertebrates evolved.
Both organs contain motion-detecting hair cells, like those in the human inner ear used for hearing and balance. Ear drum movements in birds, and jaw movements in fish, respectively distort the PTO and spiracular organ, triggering the hair cells.
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Image: PTO organ with hair cells labelled in green
Credit: Paul O'Neill
Reproduced courtesy of the University of Cambridge
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Natural barometer in birds evolved from ancient fish sense organ
5 September 2012
New research indicates that a bird’s ability to detect changes in air pressure is the evolutionary remnant of an ancient sense organ found in sharks and sturgeons.