In a stunning twist to our understanding of evolutionary history, an international team of scientists has revealed that the earliest known vertebrates possessed not two, but four image-forming eyes. The research, centered on exquisitely preserved 518-million-year-old fossils from the Chengjiang biota in China, was published in Nature.

The fossils belong to two species of myllokunmingiids—primitive, fish-like vertebrates that swam during the Cambrian Period. While their paired lateral eyes were already recognized, advanced imaging techniques have now identified a second pair of smaller, dorsally positioned organs between them. These contain dense layers of melanin-rich cells (melanosomes), identical to those in the retinal pigment epithelium of modern camera-type eyes, and distinct lens-like structures.

This compelling evidence suggests that both sets of organs functioned as sophisticated visual systems capable of forming images. The dorsal pair likely corresponds to the pineal complex—a structure retained in many living vertebrates as a light-sensitive but non-image-forming “third eye.”

The discovery overturns long-held assumptions that early vertebrates had simple visual systems. Instead, it appears that a four-eyed configuration may have been the ancestral vertebrate condition, offering a wider field of view for detecting predators or navigating complex Cambrian seas. Over time, evolution streamlined this system, with the dorsal eyes losing their image-forming capacity in later lineages.

According to the researchers, this finding not only illuminates the deep evolutionary origins of vertebrate vision but also underscores how early life experimented with complex sensory solutions during the “Cambrian explosion”—a period of dramatic biological innovation.

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Reference

Lei, X., Zhang, S., Cong, P. et al. Four camera-type eyes in the earliest vertebrates from the Cambrian Period. Nature (2026). https://doi.org/10.1038/s41586-025-09966-0