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Nature:寒武纪的奇虾眼睛含有16000个水晶体

2011/12/08 来源:sciencemag
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古生物学家最近在保存的非常好的动物眼睛印痕化石中发现了奇虾的标本,发现这种奇怪生物的眼睛就像蜻蜓一样,拥有多达16000的水晶体。

大约5亿年前,寒武纪海洋是美妙离奇的掠食动物奇虾(Anomalocaris)的家园。

这种生物,多见于艺术家的想象中,它们是节肢动物的远亲。它们的眼睛长在肉肢上,一张圆嘴包含着连锁的盘,就像遮挡相机镜头的盖子。

这些特征使得古生物学家认为奇虾(Anomalocaris)对于像蠕虫和三叶虫之类的生物来说是一种可怕的捕食者。不过,一直到现在,这种动物到底是如何发现它们的猎物的还依然是个谜。

在一项发表在《nature》上的新研究中,古生物学家报告说,他们在保存非常好的动物眼睛的印痕化石中发现了奇虾(Anomalocaris)的罕见标本。

很显然,这种生物的每个眼睛至少含有16000个六角形水晶体,使得它们具有和蜻蜓类似的高清视觉。

这篇论文的作者认为,奇虾(Anomalocaris)拥有如此犀利的视力可能是早期进化“军备竞赛”的一部分。

由于捕食者进化出了更好的视觉,它们的猎物则必须发展出更好的护甲或者其他的防御措施。和奇虾(Anomalocaris)躲猫猫显然是一项危险的游戏。


Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes

John R. Paterson, Diego C. García-Bellido, Michael S. Y. Lee, Glenn A. Brock, James B. Jago & Gregory D. Edgecombe

Until recently, intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerstätten. The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods4, but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2–3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris. Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision—such as Anomalocaris—within the early Cambrian ecosystem probably helped to accelerate the escalatory ‘arms race’ that began over half a billion years ago.

文献链接:http://www.nature.com/nature/journal/v480/n7376/full/nature10689.html

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