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The Trilobite Eye A Wonder of Complex Design

Some of the first preserved fossils were trilobites. Most paleontologists thus consider trilobites to be one of the most ancient of known fossil groups. Fortunately, a large number of well-preserved examples exist, which allows a detailed study of the animal. As a result, much is known about its well-designed, complex eye. New research on the workings of the trilobite eye shows that it is far more complex and better designed than thought even just a few years ago. Such a discovery is contrary to evolution theory.

trilobiteTrilobita is a large class of extinct marine bottom-dwelling arthropods (a group including insects, spiders and crustaceans like lobsters) that were abundant in the Cambrian and Silurian seas. Fossilized trilobites are commonly found in many parts of the world. The large number of well-preserved examples has allowed detailed studies of the animal’s anatomy. They possessed the first known “compound” (multi-lensed) design type of eye (specifically the diopter apparatus) that preserves very well in the fossil record. The once misnamed “simple primitive” trilobite eye is now known to incorporate an incredibly complex optical-chemical system into its design. Marine bioogist Richard Ellis called the “compound eyes of trilobite… with their hundreds of lenses… far more complicated than the eyes of any vertebrates” (2001, p. 7). Scientists claim that the trilobite not only had: “highly organized visual organs, but some of the recently discovered properties of trilobites’ eye lenses represent an all-time feat of function optimization… a very successful scheme of eye structure: the composite or compound eye.” (Levi-Setti, 1993, p. 29).

The trilobite eye is the “oldest eye of which we have record” (Sinclair, 1985, p. 9). Trilobites lived, by evolutionist reckoning, over 500 million years ago. Duke-Elder wrote a half century ago that a major problem for vision evolution is that “among the earliest fossils known to man” the Trilobites, Arthropods which crept over the sea-bed… both median ocelli [simple eye] and lateral compound eyes were present which have reached a high stage of complexity ” (1958, pp. 156-157). Trilobite scientists now conclude that trilobites “possessed the most sophisticated eye lenses ever produced,” and their vision may actually have “been superior to current living animals” (Shawver, 1974, p. 72). Based on careful examination of fossils, researchers have concluded that trilobites could see exceptionally well, even though they often lived in the deep (thus very dark) sea bottom. One reason why is that their eye lenses were designed specifically to function in low-light, watery environments.

A compound eye is constructed from a large array of separate eye optical elements called ommatidia. Each eye component (ommatidium) was pointed in a different direction, allowing the trilobite to simultaneously see in front, on each side, and behind it, giving it a panoramic view of the world (Fortey, 2004, p. 449). A network of photoreceptors and neurons then translated the many optical images picked up by the compound eye into a single composite picture. Evidence of the effectiveness of this eye design is the fact that it is still widely used in both insects and crustaceans today (Levi-Setti, 1993, p. 29).

One example of the excellent trilobite design was the eye lens used on each ommatidium (Fernald, 1997; 2001). The corneal lens faced the outside world. It was constructed of clear calcite crystals, a hard mineral with very unique optical properties, well suited for underwater vision. The calcite lens also makes trilobites unique in the entire animal kingdom (Fortey, 2000, p. 92). Most eye lenses are the “soft” type constructed out of cuticle. The trilobite calcite lens design used two separate layers called a doublet, each with different optical properties that functioned together as a unit to focus the image.

Trilobite eyes were usually hexagonally shaped, but some used square elongated clear calcite prisms (Fortey, 2000, p. 96). The result was a design that had a huge advantage in low light, even compared to most modern eyes. The lens used a design that largely eliminated the spherical aberration problem, the distortion caused by the lens shape (Fortey, 2004, p. 449). Spherical distortion occurs when the image is less sharp and slightly distorted, especially at the lens periphery compared to the centre of the lens. Levi-Setti wrote that: “This optical doublet is a device so typically associated with human invention that its discovery in trilobites comes as something of a shock. The realization that trilobites developed and used such devices half a billion years ago makes the shock even greater. And a final discovery that the refracting interface between the two lens elements in a trilobite’s eye was designed in accordance with optical constructions worked out by Descartes and Huygens in the mid-seventeenth century “borders on sheer science fiction” (1993, p. 54).

A large amount of variety exists in the eye design of the estimated 200 different trilobite species. Research has found that specific trilobite eye design varied according to the light environment in which the trilobite lived (Clarkson, 1975). Some trilobites had eyes with a few lenses; other types had eyes with lenses numbering in the thousands. Some eyes were enormous, taking up most of the surface of the head. The most common eye design was a turret shape that produced a combined visual field that covered the animal’s entire surroundings (Levi-Setti, 1993, p. 32). Three basic designs exist: the holochroal, the schizochroal, and the abathochroal.

The holochroal variety was both the most common trilobite eye type and also the most complex. This design consisted of thousands of small hexagonal-shaped lenses that function together as a unit. Each lens used a shelled, biconvex design consisting of a thin calcite layer covered by a thin protective film. This design is found in all trilobite orders and in many different species. Trilobites in sediments above the Cambrian had thicker lenses.

The second trilobite eye type, the aggregate or schizochroal eye, was similar to the holochroal type except that it had fewer and larger biconvex lenses that were set in a turret-like arrangement separated by a hard fibrous membrane. This “highly sophisticated” eye design is found only in the trilobite order Phacopida, and is a “visual system quite different from any other eye that has ever appeared in the animal kingdom” (Fortey, 2004, 449; Levi-Setti, 1993, p. 43). The juvenile holochroal eye resembled a schizochroal eye, and Darwinists believe that it represents the retaining of ancestral juvenile characteristics into adulthood (Clarkson, 1975). This eye type appeared fully formed in the fossil record at higher levels of Cambrian rock.

The last basic trilobite eye type, the abathochroal form, resembles a schizochroal eye, except that it does not have membranes between each individual lens. This design is found in only a few types of Cambrian trilobites.

Some eyeless trilobite species also existed, all of which lived in the darkness of the deep sea floor below the sunlit zone (Fortey, 2004, p. 449). Instead of labeling these trilobites more primitive than sighted trilobites, and because lobsters and other crustaceans that lived on the deep sea floor were eyeless, evolutionists speculate that the eyes of these trilobites were slowly lost during evolution. The Darwinist’s explanation of the origin of the trilobite eye is that: “Through natural selection operating on chance variations” trilobites evolved a remarkably sophisticated optical system. For an optical engineer to develop such a system would require considerable knowledge of such things as Fermat’s principle, Abbe’s sine law, Shell’s laws of refractions, the optics of birefringent crystals, and quite a bit of ingenuity” (Stanley and Raup, 1978, p. 182).

Although trilobite eyes are well preserved and abundant in the fossil record, no evidence exists of their evolution. They appear fully formed in the fossil record. Levi-Setti concluded the external similarities of the “primitive” trilobite eye “to those of some modern insects (for example, the ant) is quite remarkable” (1993, p. 34). This man wrote that the schizochroal eye “probably evolved from the holochroal eye,” but this conclusion is based solely on comparisons of outward appearance, not fossil evidence of transitional forms.

The trilobite eye is the earliest known eye existing in the fossil record, yet it is extremely well designed. It is not a primitive eye in any way, but a highly advanced and highly effective eye, especially given the trilobites’ typical environment at the bottom of deep water that is normally close to completely dark. As Shawver wrote, trilobite eyes are an “impressive feat of early evolution,” but even though trilobites were the most prevalent animal in the Cambrian Sea, no evidence of trilobite eye evolution exists “in spite of an abundant fossil record dating back to the early Cambrian (1974, pp. 72-73). Lack of empirical evidence has forced scientists to speculate on the path of trilobite eye evolution and, for this reason, historically, “views on eye evolution have flip-flopped, alternately favoring one or many origins” Fernald, 2006, p. 1917).

The most that scientists can now say is we “have some understanding of how eyes might have evolved” Fernald, 2004 p. 141 emphasis mine). As Levi-Setti concluded, the “real surprise” is not that the eyes functioned according to the laws of physics, but that their “basic lens designs” were engineered “with such ingenuity” (1993, p. 54). This evidence contradicts Darwin’s prediction that the earliest eyes were primitive, and that a large number of transitional forms, suggestive of eye evolution from simple to complex, would be found in the fossil record (1859). This is certainly food for thought!

Jerry Bergman
December 2007

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