Ancient trilobites had crystal eyes, still a mystery: ScienceAlert

Nature has tried some wild approaches to life’s problems over the ages, and that’s true of vision.

Perhaps one of the earliest examples of a complex eye relied on a somewhat unusual material to focus light, a material not found in modern organisms. The eyes belong to an extinct group of animals called trilobitesAnd their eyes were made of a hard crystal, a mineral known as calcite — a little oddity that gives us a window into how these early animals sensed the world around them.

Trilobites became extinct about 250 million years ago but existed about 300 million years before that. There are also a lot of three-lobed body plans in the fossil record, indicating that those 300 million years ago were very successful. And because their strange eyes were made of stone, they are beautifully preserved in the many fossils they leave behind.

This is how we know that trilobites have it compound eyes Like insects, it is made up of groups of photoreceptor units called photoreceptors ommatidiaEach has its own photoreceptors and lenses. Examinations of the fractured sections of the fossilized lenses reveal the presence of a crystalline material made of calcite.

Pure calcite is transparent, so, in theory, light can pass through it and focus, where photoreceptors can detect it. As with seeing insects, there it was Most likely a trade off: It may not have seen trilobites with such high spatial resolution, but it was particularly sensitive to motion.

There were three types of these trilobite eyes. The oldest and most common is the type known as Holochroalin which the small ommatidia were covered by a single corneal membrane, with the adjacent lenses in direct contact with each other.

The slinging eye is only seen in the family Udiskiday; Small lenses are covered with a thin cornea.

Finally, the schizophrenic eye is seen only in Vakobina monotonous. The lenses are larger, widely separated, and each has its own cornea. Scientists think they were likely, High degree of specialization.

The holocral eye is most similar to the modern eye Eyes watching It has been seen in some insects and crustaceans, and scientists believe it worked in a similar way. Each omatidium works individually, and the photo that the insect sees is Mosaic for all images combined.

However, things get a little tricky with calcite. Calcite has one of the strongest refractions in nature. This means that it has two refractive indices; It will be light split twice As it travels through the calcite, the two rays travel at different speeds, producing a double image.

For small ommatidia, as seen in the all-seeing eye, that is It’s not likely to be a problem; The deviation in the rays is smaller than that of the light sensing organ.

For schizoid eyes, refraction is more of a problem. The crystal is not flexible, so larger ommatidia cannot change their focus to reduce the effect. Instead, the scientists found that schizoid eyes have what is known as a Dual lens structure.

This means that the lens has two layers, each with a different refractive index, that can correct for refraction, just like trilobites have built-in glasses. Lenses of this type were invented separately by mathematicians René Descartes and Christian Huygens in the Seventeenth Centuryunaware that the trilobites had knocked them out with the punch.

For all our understanding of the different structures of the trilobite eye, we still don’t fully understand how the schizoid eye works, whether it was similar to a locus eye or did something different, such as different structure I will suggest.

Bringing us closer, a recent study shows that schizoid eyes are much more complex than we thought. Each lens is found to cover its own small compound eye, forming a sort of ‘hyper-eye’.

It may be possible that we are completely wrong about trilobite vision. 2019 study questions Whether the calcite corneas are artifacts of a preservation process, meaning their crystal eyes are far less distinct than many conjectures.

We still don’t know why this type of eye appears – if it appears at all – or what benefits it confers, but now scientists are studying trilobite vision. A new way of looking at it.