Meeting Abstract
The fossil record of arthropod compound eyes shows different modes and processes of eye reduction, sometimes leading to the loss of the eyes altogether. The first reason for having small, reduced eyes is to be a tiny organism with simply not enough space for establishing a regular compound eye. We find such a miniaturised system in the first planktonic trilobite so far known Ctenopyge ceciliae (Clarkson & Ahlberg, 2002) [trilobites: extinct arthropods, dominant during the Palaeozoic]. A reduction of compound eyes, or parts thereof, also occurs, if selective pressure for a high specialisation of eyes makes several facets fuse into a single functional unit. This possibly can be found in phacopid trilobites, ~400 million years old. Opaque conditions are often coupled with major extinction events during the Earth history, as in the late Permian, when more than 90% of all species died out. At other times, especially in many trilobites during the late Devonian, the reduction of eyes, often leading to total eye loss, has been documented in great detail, but in the same way it is intriguing to consider that certain coeval forms remained with good, unreduced compound eyes. In some trilobites eyeloss was compensated by the development of “compound noses”. For different reasons the fossil record presents only very limited evidence about parasites, in which the eyes are often reduced or absent. Possibly a few blind Agnostids, distant relatives of trilobites during the Lower Palaeozoic, may have been parasitic, and there are blind fleas preserved in amber, which have not changed very much since the Mesozoic era. Pentastomids (Crustacea), worm-like parasitic organisms, already present in the Cambrian (~487Ma), have eyeless from the very beginning. Finally, blind deep-sea organisms are documented by the fossil record.
