Overview
- Using contrast-enhanced microCT and 3D modeling, researchers identified telephone-cord-like loops in the optic nerves of multiple, distantly related chameleon species.
- The coils extend each nerve to as much as roughly three times the straight brain-to-eye distance, supplying slack that enables wide, independent scanning before precise binocular targeting of prey.
- Embryonic imaging of veiled chameleons showed the nerves start straight and twist into loops by hatching, indicating the structure forms late in development.
- Comparative scans of more than 30 reptiles, including three chameleons from different lineages, found the coiled design in chameleons but not in other lizards or snakes examined.
- Non-destructive imaging corrected misreadings from historical dissections, and the authors propose the coils may have evolved to compensate for chameleons’ stiff necks, a premise that awaits further testing.