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, 114 (51), 13489-13494

Structure and Function of a Compound Eye, More Than Half a Billion Years Old


Structure and Function of a Compound Eye, More Than Half a Billion Years Old

Brigitte Schoenemann et al. Proc Natl Acad Sci U S A.


Until now, the fossil record has not been capable of revealing any details of the mechanisms of complex vision at the beginning of metazoan evolution. Here, we describe functional units, at a cellular level, of a compound eye from the base of the Cambrian, more than half a billion years old. Remains of early Cambrian arthropods showed the external lattices of enormous compound eyes, but not the internal structures or anything about how those compound eyes may have functioned. In a phosphatized trilobite eye from the lower Cambrian of the Baltic, we found lithified remnants of cellular systems, typical of a modern focal apposition eye, similar to those of a bee or dragonfly. This shows that sophisticated eyes already existed at the beginning of the fossil record of higher organisms, while the differences between the ancient system and the internal structures of a modern apposition compound eye open important insights into the evolution of vision.

Keywords: Cambrian; arthropod; compound eye; evolution; visual system.

Conflict of interest statement

The authors declare no conflict of interest.


Fig. 1.
Fig. 1.
Trilobite S. reetae Bergström, 1973 (25) (GIT 294-1) and its compound eye. (A) Holotype. (B) Head region of A. (C) Fields of view. (D) Abraded part of the right eye. Arrowheads indicate the ommatidial columns. (E) Lateral view of the right eye. (F) Schematic drawing of E. (G) Two visual units (big arrows in D). (H) Schematic drawing of G. (Scale bars: AC, 1 cm; D, 1 mm; E and F, 2 mm; and G, 200 μm.)
Fig. 2.
Fig. 2.
Internal structures of the functional visual unit. (A) Ommatidium. Note the cellular elements (relicts of receptor cells) arranged radially around the central core (relict of the rhabdom). (B) Ommatidium positioned in a basket. Note the cellular elements (relicts of receptor cells) arranged radially around the central core (relict of the rhabdom). (C) General aspect of B for interpretation in D. (E) General aspect of A for interpretation in F. (G) Cross-section of the ommatidium of the extant crustacean Dulichia porrecta (Bate, 1857) (87) (Crustacea, Amphipoda) (88). (H) Schematic drawing of the elements of a typical sensory system in the aquatic compound eye in G. (I) Schematic drawing of a longitudinal section of an ommatidium. (J) Schematic drawing of the visual unit of S. reetae. b, basket; cc, crystalline cone; L, lens; om, ommatidium; p, pigment screen; r, rhabdom; sc, sensory (receptor) cells. (Scale bars: A, B, E, F, and J, 200 μm; C and D, 100 μm; and G, 1 μm.)
Fig. 3.
Fig. 3.
H. kjerulfi (Linnarsson, 1871) (85) (Natural History Museum at the University of Oslo, PMO 73168). (A) Head region of H. kjerulfi. (B) Left eye of A. (C) Dense facets in B, hexagonally packed. (D) Lateral aspect of the head. (Scale bars: A and D, 1 cm; B, 2 mm; and C, 500 μm.)

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