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Fossil insect eyes shed light on trilobite optics and the arthropod pigment screen

机译：化石昆虫的眼睛照亮了三叶虫光学元件和节肢动物色素屏幕

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Fossilized eyes permit inferences of the visual capacity of extinct arthropods(1-3). However, structural and/or chemical modifications as a result of taphonomic and diagenetic processes can alter the original features, thereby necessitating comparisons with modern species. Here we report the detailed molecular composition and microanatomy of the eyes of 54-million-year-old crane-flies, which together provide a proxy for the interpretation of optical systems in some other ancient arthropods. These well-preserved visual organs comprise calcified corneal lenses that are separated by intervening spaces containing eumelanin pigment. We also show that eumelanin is present in the facet walls of living crane-flies, in which it forms the outermost ommatidial pigment shield in compound eyes incorporating a chitinous cornea. To our knowledge, this is the first record of melanic screening pigments in arthropods, and reveals a fossilization mode in insect eyes that involves a decay-resistant biochrome coupled with early diagenetic mineralization of the ommatidial lenses. The demonstrable secondary calcification of lens cuticle that was initially chitinous has implications for the proposed calcitic corneas of trilobites, which we posit are artefacts of preservation rather than a product of in vivo biomineralization(4-7). Although trilobite eyes might have been partly mineralized for mechanical strength, a (more likely) organic composition would have enhanced function via gradient-index optics and increased control of lens shape.
机译：僵化的眼睛可以推断出已灭绝节肢动物的视觉能力（1-3）。但是，由于离子和成岩过程的结果，结构和/或化学修饰会改变原始特征，因此有必要与现代物种进行比较。在这里，我们报告了5400万年前的鹤蝇的眼睛的详细分子组成和微观解剖结构，它们共同为解释某些其他古代节肢动物的光学系统提供了代理。这些保存完好的视觉器官包括钙化的角膜晶状体，这些钙化的角膜晶状体被包含真木兰色素的中间空间隔开。我们还表明，在生活中的白鹤蝇的小平面壁中存在着Eumelanin，其中在包含几丁质角膜的复眼中，Eumelanin形成了最外层的色素遮盖物。据我们所知，这是节肢动物中黑色素筛选色素的第一个记录，并且揭示了昆虫眼中的一种化石模式，该模式涉及抗腐烂的生物色素以及早期的成虫成虫成虫的成虫晶状体。最初为几丁质的晶状体表皮的可证实的二次钙化对建议的三叶虫钙质角膜有影响，我们认为这是保存的假象，而不是体内生物矿化的产物（4-7）。尽管三叶虫眼的机械强度可能已部分矿化，但（更可能的）有机成分将通过梯度折射率光学器件和增强的镜片形状控制功能得到增强。

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