The trilobites, the creatures that ruled the earth before the dinosaurs, had unique eyes
More than 500 million years ago, long before the age of the dinosaurs, trilobites ruled the world: the ancestors of crustaceans and creatures with an external skeleton, some of which developed special "eyes".
The trilobites became extinct 248 million years ago, in a global climate disaster, in which more than 90% of the creatures living in those days were wiped out. Then the age of reptiles began.
The main characteristic of the trilobites - invertebrates with a hard outer shell - was the exoskeleton, reminiscent of the skeletons of cockroaches and multi-legged insects today. The soft parts of their bodies were not preserved. The smallest of the trilobite fossils, smaller than 1 mm; And the big one, known - almost 1 meter.
It is estimated that they fed mainly on carcasses, and some of them may also have been "hunters" of live prey.
The name trilobite ("three lobes"), comes to express the organization of their body structure with a longitudinal central lobe and 2 side lobes.
The visual system of some trilobites was one of the most developed among the ancient creatures from half a billion years ago. Most of them had a pair of compound eyes on either side of the "head", or in the front of their bodies. Complex eyes, built from hundreds to thousands of "simple" eyes, in which a small lens focuses light from a certain segment, on neural photoreceptors. for a beaver, for example,
His eyes are trained. But there were trilobites whose eyes were formed on the tentacles, such as the snails. And they were also eyeless.
This variety of eyes was designed for the needs of life in different environments: those who lived on the bottom of the oceans, did not need eyes, because the light did not reach the depths anyway. The advantage of compound eyes is probably in detecting movement - an important matter for predators and their victims.
Vertebrate eyes are characterized by a flexible eye-lens, which is able to change shape and adjust the focused vision to different distances. The use of a pair of eyes, together with the processing of the images in the brain, enables stereoscopic vision, in depth, which yields the distance estimate.
The trilobites probably achieved this, using many simple eyes, in the structure of the compound eye. To adjust vision for different distances, in a situation where the lens of the eye is not flexible, they used a special form of the lens made of two materials with different refractive indices.
It is a combination of two lenses ("doublet") to correct the focus of the hard lens. This form of lens was invented in the 17th century by the French physicists Descartes and the Dutch Huygens.
Dr. Noah Brosh
