I saw this photo on my Facebook page and was transfixed. It was taken by Stephen Marley, who gave me permission to post it here (the image is under his copyright). As he said on FB:
“This is a type of eye called schizochroal, photographed on a Devonian trilobite Hollardops mesocristata (there are two other major trilobite eye types and literally thousands of individual lens configurations at the species level). What’s really cool about this specimen is that the individual calcite lenses have been preserved with some sort of iron oxide, which makes them clearly stand out from the rest of the dark exoskeleton.”
Steve added later that this specimen dates from 409-394 mya and is from the Atlas Mountains of Morocco.
If you have a serious interest in evolution, you must read about trilobite eyes. They represent the first evolutionary appearance of a compound eye, and their construction and diversity are stunning. Unlike the compound eyes of insects, trilobite eyes were hard, as they were composed of the mineral calcite (calcium carbonate). As Richard Fortey quipped, this gives new meaning to the term “stony gaze.”
A good introduction to trilobite eyes is this site. It’s short, but if you don’t have the attention span at least check out the photos.
And here is a paper with an irresistible title, and some even weirder photos, “A Devonian Trilobite with an Eyeshade”, by Richard Fortey and Brian Chatterton. Fortey is a paleontologist, but also a great science writer whose books have not gotten the attention they deserve on this side of the pond. He’s the author of Trilobite!, a popular book on the beast that I recommend highly.
Note: Accessing the Fortey and Chatterton paper might require a subscription, so I’ll post the picture of the “eyeshade” trilobite eye below. It’s also from a Devonian fossil collected in Morocco, and the authors claim that these bizarre columnar eyes allowed the beast a full 360-degree view of the sea floor around it. The “eyeshade,” or overhanging lip on the top of the eye, supposedly prevented overhead light from striking the eye (see demonstration in D and E below).
Fig. 1. “Eyeshade” eye from Fortey and Chatterton paper. Here’s their caption: Erbenochile erbeni (Alberti). Devonian (Emsian) Timrahrhart Formation (Jebel Gara el Zguilma, near Foum Zquid), southern Morocco. (A) Posterior view showing overhanging eyeshades. (B) Lateral view. (C) Dorsal view. The headshield is 32 mm across. (D) Side view detail of right eye showing lenses under optimum illumination, and (E) how the eyeshade cuts out light from above, when directed as a parallel beam above the palpebral lobe.
Preparation and photography of H. mesocristata (from SM): “This specimen was prepared by Mike Thomas using skillful application of micro air-abrasive techniques to preserve the delicate details. The photo was taken with a 55mm micro-Nikkor lens on a 35mm “film based” Nikon F2 Camera using a fiber optic illumination system. The 35mm film was scanned at 2400 dpi on a Imacon Flextight scanner and converted to a jpeg file. The eye measured 8.5 mm horizontally.”
Thanks to Steve for permission and information.