Few morphological features in the entire fossil record are as singularly significant as trilobite eyes. By the time the initial members of the trilobite line appeared early in the Cambrian, slightly more than 520 million years ago, many of those arthropods already featured highly developed eyes -- marking them as the first creatures to leave behind fossil evidence of such a major evolutionary advance.
Those original eyes were crescent-shaped and in most cases seemingly provided nearly 360-degree vision for the primitive trilobite types, such as Olenellus transitans and Redlichia takooensis, which sported them. Indeed, it has been speculated that the development of trilobite eyes, and that advancement's subsequent impact on both predatory and prey animals within their primal ecosystem, helped spark the famed Cambrian Explosion.
By the Ordovician, approximately 50 million years later, trilobite eyes had developed into an almost dizzying array of sizes and shapes. Some, like those attached to Russian species such as Asaphus kowalewski and Cybele panderi, sat atop spindly “stalks” up to three inches long. This feature presumably allowed the trilobite a better view of the world around it… even when it may have been lurking under a thick layer of silt or mud along the sea bottom. Other trilobites of the time period, such as the aptly named Cyclopyge bohemica and the closely related Pricyclopyge binodosa, developed huge wrap-around holochroal eyes featuring over a thousand small, tightly packed lenses that allowed a virtually uninterrupted view of the ocean floor beneath it.
Almost 100 million years later, in the Middle Devonian, trilobite eyes had developed into the most complex optic attachments ever to see, or be seen. Eldgredgeops milleri presented schizochroal eyes featuring dozens of individual lenses stacked in rigid, symmetrical rows that provided its host with a truly unique view of the world around it.
Other Devonian trilobites, such as Erbenochile issomourensis, showcased eyes with over 200 large, individual lenses, as well as a small “brim” atop the eye column, apparently designed to shade each oculus. Rather ironically, at roughly the same time, trilobite species like Struveaspis sp. had lost virtually all the lenses of their eyes, appearing to be almost totally blind. Such evolutionary features reflected the shallow, or correspondingly deep, water environments in which these trilobites thrived, as well as the role that filtered sunlight may have played within their particular ecological niche.
Unlike any modern eyes -- whether they are anthropoid, arthropod or annelid -- the lenses of trilobite eyes were actually constructed of calcite. This provided these ancient creatures with virtually unparalleled vision that we can assume (thanks to recent experiments conducted with calcite crystals) was filled with streams of light and bursts of color.
With the “space-age” geometric symmetry presented by each lens, these eyes seem to defy their incredibly ancient ancestry. And when we today stare into the fossilized eyes of a trilobite, it takes only minimal imagination to sense that these primeval creatures may indeed be staring back at us, providing a dramatic link to life some 500 million years in the past.
Here's a look at some of the most amazing eyes in the world of trilobites:
The largest trilobite eye: Fenestraspis amauta, Devonian, Bolivia... 2.2 cm in height.
The stalked eyes of Asaphus kowalewski could reach three inches in length, providing this Ordovician trilobite from Russia with one of the most alien appearances in the fossil world.
The primitive, crescent-shaped eyes of Olenellus transitans allowed it to be among the first creatures with sight in the entire history of Planet Earth.
The stalked eyes of Cybele panderi provided the trilobite with excellent vision… even when it was covered in mud along the sea floor.
Thousands of tiny lenses construct the eye of Pricyclopyge binodosa, which in life wrapped around and under the trilobite's head.
The giant eye (1.9 cm) of Pricyclopyge sp. from the Ordovician of England is covered in thousands of separate lenses.
Eldgredgeops milleri possesses perhaps the most studied eye in trilobite history. Such research has helped map its migratory and evolutionary pattern.
The huge eye of Erbenochile issomourensis is one of the largest among trilobites. Note the small “brim” at the very top of the eye column.
Struveaspis moroccanica from the Devonian of Morocco developed a unique eye.
The amazing holochroal eye of Scutellum sp., a Devonian trilobite from Morocco.
The wrap-around eyes of Symphysops stevaninae provided this Devonian trilobite with vision of the entire sea floor.
By the Late Devonian, some phacpoids, such as this Eocryphops sp., had seen their lens count drop to a precious few.
Conocryphe sulzeri was a blind trilobite, indicating a life in deep water where vision was not an evolutionary advantage