Trilobite vision: A comparison of schizochroal and holochroal eyes with the compound eyes of modern arthropods

  • Fordyce D
  • Cronin T
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An analysis of trilobite vision is strengthened by the use of new mathematical approaches to compound eye design. In particular, the product of the facet diameter (D) and the interommatidial angle (??) gives the value of the eye parameter, D??, which is a reliable indicator of the photic conditions in which the eye was used. In modern arthropods, D?? values range from 0.3 for animals active in bright sunlight to 20 or more for nocturnal or deep-sea animals. Two major types of compound eyes existed in trilobites: schizochroal and holochroal. In this paper, we have examined holochroal compound eyes in Asaphus cornutus, Isotelus gigas, and Homotelus sp. Holochroal eyes contain far more ommatidia than do schizochroal types, reducing both facet diameter (D) and interommatidial angle (??). Thus, D?? values in these species fall into the same range as in modern nocturnal compound eyes. This implies that function of the holochroal eye was similar to that of modern arthropods, and that they were used in moderate to dim intensities of light. -from Authors

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  • David Fordyce

  • Thomas W. Cronin

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