"We have shown that there is a fundamental adaptive mechanism linking a species' locomotion with the sensory systems that process information about its environment," says Alan Walker, Evan Pugh Professor of Anthropology and Biology at Penn State University, one of the team's leaders. The researchers studied 91 separate primate species, including all taxonomic families. The study also included 119 additional species, most of which are mammals ranging in size from mouse to elephant, that habitually move in diverse ways in varied environments.
The project is the first large-scale study to document the relationship of the dimensions of the semicircular canals to locomotion. These structures are filled with a fluid, which moves within the canals when the animal moves. The fluid's movement is sensed by special cells that send signals to the brain, triggering the neck and eye muscles to reflexively keep the visual image stable.
By mapping the structure of the balance organ to each style of movement they have created a map for comparison of extinct species. Example, baboons have much more development of the semicircular canal than sloths. Humans have more than baboons. Given a skull fragment with most of the canal structure in it and a CAT scanner to image it, you can arrive at a general idea of what kind of animal it was.
The basic hypothesis of the project was that the organ of balance -- which helps stabilize an animal's gaze and coordinate its movements as it travels through the environment -- should be irrevocably linked to the type of locomotion produced by its limbs. "If an animal evolves a new way of moving about the world, its organ of balance must evolve accordingly," Walker explains. From the visual information, the animal tracks its position relative to stationary objects such as tree trunks, branches, rocks or cliffs, or the ground. Having a stable image of the environment is especially crucial for acrobatic animals that leap, glide, or fly.
Damn that's clever eh? I love cleverness like that.