Jakarta –
Recently, researchers found an ancient animal with crystal eyes. Trilobites, ancient animals from around 300 million years ago, were recorded as having eyes made up of the mineral calcite.
Trilobites are a type of ancient animal that became extinct about 250 million years ago. However, before the extinction of these animals are believed to have inhabited the Earth for 300 million years.
The adaptation of life to nature is often one of the things that make animals have this amazing structure. Living hundreds of millions of years ago, these ancient animals could have unusual structures that modern organisms don’t have, as quoted from Science Alert.
Primordial Animal Crystal Eyes
The complex eyes of ancient Trilobites relied on an unusual material to focus light. This is because their eyes are made of hard crystals, a mineral known as calcite.
Knowledge of the crystals in the eye was discovered when researchers examined parts of the eye lens that were damaged but well fossilized. It was this eye fossil that revealed that the crystalline material in the eye consisted of calcite.
Trilobite Eye Types
Interestingly, these animals also have compound eyes like insects. Each eye is made up of a collection of photoreceptor units called ommatidia and their respective lenses.
Its oldest and most common eye is known as the holochroal. The tiny ommatidia photoreceptors are covered by a single corneal membrane. The lenses are close together in direct contact.
Well, holochroal is the type of eye of an ancient trilobota animal that most closely resembles the appositional eye of modern insects and crustaceans. This finding led scientists to believe the eyes of trilobates and insects would have worked in a similar way.
In the insect’s eye, each ommatidium will work individually so that the image seen by the insect is a mosaic of all the images combined.
Next is the abathochroal eye which is only owned by Eodiscidae. This type of eye has tiny lenses and each lens is covered by a thin cornea.
Finally, schizochroal eyes which can only be found in the Phacopina suborder. The lenses of these eyes are larger, widely separated, and each has its own cornea.
Why Can Ancient Animals Have Crystal Eyes?
Studies in 2019 have questioned whether calcitic corneas can be the result of a preservation process. If so, then Trilobite crystal eyes are much more common than many think.
However, the reason why calcite crystals appeared in the eyes of these ancient animals was not known until now. In the meantime, scientists studying the vision of Trilobites can predict how these eyes work.
Note that pure calcite is transparent so that in theory, light could pass through it and be focused, where photoreceptors might detect it. It is predicted that trilobites may not see at high resolution, but they are very sensitive to motion.
However, calcite has one of the strongest birefringences in nature. This means that light is split in half as it passes through the calcite. The two rays will travel at different speeds resulting in a double image.
However, in small ommatidia like those of holochroal eyes, this would not be a big problem. This is because in this type of eye, the deviation of the rays is smaller than that of the light-sensing organs.
However, double refraction can be a problem for schizochroal eyes. This is because the crystals are not flexible, so the larger ommatidia cannot change their focus to mitigate the effect.
Instead, scientists have discovered that schizochoral eyes have what is known as a doublet lens structure. That is, the lens has two layers with different refractive indices.
Structures in the schizochroal eye can improve double refraction, so trilobites seem to have built-in glasses. The doublet lens was invented by mathematicians Rene Descartes and Christian Huygens in the 17th century.
Recent studies have revealed that the schizochroal eye is much more complex than we assume, this finding moves us closer to understanding this eye type.
In schizochroal eyes it is also found that each lens will cover its own small compound eye so that it will form a kind of hyper-eye.
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2023-07-13 12:00:03
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