Freckled Trilobites Had Great Eyes
Darlings of the Cambrian Explosion, trilobites had spotted markings and sophisticated eyes. Some have been exceptionally well preserved as fossils, down to the level of individual cells.
The compound eyes of trilobites had dozens of individual lenses, each with complex photoreceptor organs at the base. They were described by Science Now, “Looking a Trilobite in the Eye,” as like those of today’s insects and crustaceans.
The sensory cells underneath the lenses, however, were ephemeral, and scientists had always assumed that they had decayed without a trace.
So imagine Brigitte Schoenemann’s surprise when she spotted fossilized versions of these delicate sensory cells while x-raying a long dead trilobite with a computed tomography (CT) scanner. “I expected that we would see [something] in the lens of trilobites, but then suddenly we saw structures of cells below the lens,” recalls Schoenemann, a physiologist at the University of Bonn and the University of Cologne, both in Germany. Inspired, she applied to take more fossils to the European Synchrotron Radiation Facility in Grenoble, France, where she could use a particle accelerator’s high energy x-rays to peer deeper into the trilobites’ eyes. Now, she says, she’s created images of the extinct animal’s entire visual system, down to the level of fossilized individual cells.
So what does the inside of a trilobite eye look like? A bit like a flower, Schoenemann and a co-author report online today in Scientific Reports. Beneath each lens, round sensory cells are arranged like petals around a diamond-shaped photoreceptor able to pick up the dim light that filtered down through the Earth’s ancient oceans. Pigment cells filled in the space between the blooms and likely made trilobite eyes appear brownish-black.
The article said this discover brings researchers “one step closer to understanding the evolution of vision,” and that new lab techniques have “brought out really new knowledge … about the early evolution of eyes.” Richard Fortey at London’s Natural History, commenting on the fact that these eyes resemble those of living horseshoe crabs, said, “If you have an optical system that works, it can last.” He didn’t comment on how the trilobite eye arose in the first place. The first trilobites already had compound eyes.
Trilobites could see well in their environment, but might not have wanted to be seen. A paper in Geology reported spotted patterns on the shells of some exquisitely-preserved trilobite fossils found in New York. The authors speculated they might have been for camouflage. National Geographic described the techniques the team used to conclude the spots were original, not artifacts of the fossilization process (see also Live Science and Nature). The specimens had some 500 calcite-filled spots arranged in patterns that might have scattered light and blurred the image of the animal to passing predators.
National Geographic suggested many other trilobites may have had these markings. As for their function, the article “cautioned against ascribing a function for the spots on an extinct organism, noting that it’s very difficult to know for sure how the animal used them.”
Speaking of the Cambrian Explosion, another phylum joins the forty or so phyla that “emerged” without ancestors at the base of the Cambrian. Nature reported that acorn worms (tubiculous enteropneusts) alleged to be 500 million years old have been found in the Burgess Shale in Canada, suggesting to the authors that “hemichordates originated at the onset of the Cambrian explosion.” Exactly how they “originated” fully formed was not explained. Flexing his thesaurus, though, Henry Gee tried to spin an evolutionary tale out of the finding in a companion piece in Nature:
However, the question remained: how did a large, free-living worm evolve into the minuscule tube-dwelling pterobranch that filters detritus from sea water using an elaborate crown of tentacles. The fossil record preserves all kinds of possibly intermediate morphologies between one creature and another. But the record is notoriously delphic, if not laconic, and on this subject it has even less to say than usual. Enteropneusts, being soft-bodied, do not preserve well as fossils: their record in stone is exiguous in the extreme.
Readers may wish to look up some of those words, but here’s a hint: they have to do with paucity of evidence, such that a variety of conflicting stories can be concocted from the same observations.
Is it credible to believe that trilobite fossils are hundreds of millions of years old? There are numerous problems with the idea. One is the fact that they appear abruptly in the record, fully formed, with no ancestors displaying a record of “the early evolution of eyes.” Another is the fact that horseshoe crabs are similar to trilobites in many ways. Horseshoe crabs are living fossils by themselves, having appeared abruptly, supposedly existing over 450 million years with no changes to the present. Lastly, the trilobite fossils show exquisite preservation, down to the level of spots and individual photoreceptor cells below the clearly-defined lenses. Why do we continue to buy into the evolutionary story and timeline? It makes no sense in light of the evidence.
If former Nature editor Henry Gee admits that the evidence for evolution of complex Cambrian animals is delphic, he has confessed that evolutionary science is not much better off than the ambiguous divinations of well-paid Greek priestesses babbling under the influence of gas.