The sophisticated visual system of a tiny Cambrian crustacean: analysis of a stalked fossil compound eye

Abstract

Fossilized compound eyes from the Cambrian, isolated and three-dimensionally preserved, provide remarkable insights into the lifestyle and habitat of their owners. The tiny stalked compound eyes described here probably possessed too few facets to form a proper image, but they represent a sophisticated system for detecting moving objects. The eyes are preserved as almost solid, mace-shaped blocks of phosphate, in which the original positions of the rhabdoms in one specimen are retained as deep cavities. Analysis of the optical axes reveals four visual areas, each with different properties in acuity of vision. They are surveyed by lenses directed forwards, laterally, backwards and inwards, respectively. The most intriguing of these is the putatively inwardly orientated zone, where the optical axes, like those orientated to the front, interfere with axes of the other eye of the contralateral side. The result is a three-dimensional visual net that covers not only the front, but extends also far laterally to either side. Thus, a moving object could be perceived by a two-dimensional coordinate (which is formed by two axes of those facets, one of the left and one of the right eye, which are orientated towards the moving object) in a wide three-dimensional space. This compound eye system enables small arthropods equipped with an eye of low acuity to estimate velocity, size or distance of possible food items efficiently. The eyes are interpreted as having been derived from individuals of the early crustacean Henningsmoenicaris scutula pointing to the existence of highly efficiently developed eyes in the early evolutionary lineage leading towards the modern Crustacea.

Description and interpretation of the internal structure of a Cambrian crustacean compound eye

“…Ever since the "Orsten" fossils were first discovered, they offered new insights into Cambrian life, including the anatomy of early arthropods (e.g., Müller 1979aMüller , b, 1983Müller , 1985Müller & Waloszek 1985, 1987Waloszek 1993, Waloszek & Müller 1990, 1998aMaas et al 2003;Ahlberg et al 2005;Waloszek et al 2007;Haug et al 2009Haug et al , 2010aSchoenemann et al 2012). "Orsten" fossils, originally isolated from upper Cambrian limestone concretions collected in southern Sweden, have now been found worldwide (Maas et al 2006).…”

Mineralized rods and cones suggest colour vision in a 300 Myr-old fossil fish

“…Except for the optical system, as in the calcified lenses of trilobite and ostracod arthropods, other parts of the visual system are not usually preserved in the fossil record, because the soft tissue of the eye and the brain decay rapidly after death, such as within 64 days and 11 days, respectively 7 . Only five studies have reported a fossilized visual receptor [8][9][10][11] or a mould equivalent 12 , all of which involved arthropod eyes. The lack of receptor preservation in fossilized vertebrate eyes has limited their comparison with the eyes of extant relatives.…”

The clever strategy of a tiny crustacean eye early in the evolution of vision

“…1AB2) (compare ref. 21, Fig 1C). In the ‘cyclopic’ forms such as Cambropachycope clarksoni Walossek and Müller 1990 it is even probable for example to show, that probably polarized light was used for predation, an astonishing convergence with the tactics used by living predatory waterfleas 22 .…”