Trilobite eyes: most complex found (Introduction)

by David Turell , Wednesday, July 12, 2023, 15:38 (501 days ago) @ David Turell

New studies:

https://www.sciencealert.com/ancient-trilobites-had-crystal-eyes-and-theyre-still-a-mys...

"...we know that trilobites had compound eyes like insects, consisting of clusters of photoreception units called ommatidia, each with its own photoreceptors and lenses. Examinations of broken sections of the fossilized lenses reveal a crystalline material made of calcite.

"Pure calcite is transparent, so, in theory, light could penetrate it and be focused, where the photoreceptors might detect it. As with insect vision, there was likely a trade-off: Trilobites probably didn't see in high spatial resolution, but they were particularly sensitive to motion.

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

"The abathochroal eye is only seen in the family Eodiscidae; the small lenses are each covered by a thin cornea.

***

"Finally, the schizochroal eye is only seen in the Phacopina suborder. The lenses are larger, widely separated, and each has its own cornea. They were probably, scientists believe, highly specialized.

"The holochroal eye is the most similar to modern apposition eyes seen in some insects and crustaceans, and scientists believe they worked in a similar way. Each ommatidium operates individually, and the image the insect sees is a mosaic of all the images combined.

"...scientists have found that schizochroal eyes have what is known as a doublet lens structure.

"That means the lens has two layers, each with a different refractive index, that could correct for birefringence, almost like the trilobites had built-in spectacles. Lenses of this type were invented, separately, by mathematicians Rene Descartes and Christian Huygens in the 17th century, unaware that trilobites had beaten them to the punch.

"For all our understanding of the various structures of the trilobite's eye, though, we still don't quite understand how the schizochroal eye worked, whether it was similar to an apposition eye or did something differently, as the different structure would suggest.

"A recent study showed schizochroal eyes are far more complex than we thought, which brings us closer. Each lens was found to cover a small compound eye of its own, forming a sort of "hyper-eye".

Comment: there are no earlier eyes!! Trilobites just simply appear. This just intensifies the meaning of the Cambrian gap.