What makes cheetahs, the world's fastest land animal, a successful hunter is not just their speed. Much of the credit must also go to their one-of-a-kind inner ear that helps them keep their gaze locked on prey during high-speed hunting, suggests new research.
The inner ear is an organ that is essential for maintaining body balance and adapting head posture during movement in most vertebrates.
The study, published today in the journal Scientific Reports, found that the inner ear of modern cheetahs is unique and likely evolved relatively recently.
"If you watch a cheetah run in slow motion, you'll see incredible feats of movement: its legs, its back, its muscles all move with such coordinated power. But its head hardly moves at all," said lead author Camille Grohe from American Museum of Natural History in New York.
"The inner ear facilitates the cheetah's remarkable ability to maintain visual and postural stability while running and capturing prey at speeds of up to 65 miles per hour (over 100 kms an hour). Until now, no one has investigated the inner ear's role in this incredible hunting specialization," Grohe said.
In the inner ear of vertebrates, the balance system consists of three semicircular canals that contain fluid and sensory hair cells that detect movement of the head.
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Each of the semicircular canals is positioned at a different angle and is especially sensitive to different movements: up and down, side-to-side, and tilting from one side to the other.
The researchers used high-resolution X-ray computed tomography (CT) to scan the skulls of 21 felid specimens, including seven modern cheetahs from distinct populations, a closely related extinct cheetah that lived in the Pleistocene between about 2.6 million and 126,000 years ago, and more than a dozen other living felid species.
With those data, they created detailed 3-D virtual images of each species' inner ear shape and dimensions.
They found that the inner ears of living cheetahs differ markedly from those of all other felids alive today, with a greater overall volume of the vestibular system and longer anterior and posterior semicircular canals.
"This distinctive inner ear anatomy reflects enhanced sensitivity and more rapid responses to head motions, explaining the cheetah's extraordinary ability to maintain visual stability and to keep their gaze locked in on prey even during incredibly high-speed hunting," said coauthor John Flynn from American Museum of Natural History.
These traits were not present in the extinct species examined by the researchers, which suggests the recent evolution of the highly specialised inner ear of modern cheetah.
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