Isolated sheets of resistant material in the fossil record are routinely referred to as cuticle or cuticle-like sheets; early records of this type of microfossil include specimens from the Early Ordovician of Tunisia (Combaz, 1967) and early Middle Ordovician of Saudi Arabia (Le Hérissé et al., 2007). The affinities of the organisms that produced the cuticle were probably very diverse and included not only plants, but animals, fungi, and perhaps lichen-like associations. Although most cuticle sheets lack distinctive ornamentation, similar to those of Nematothallus (Edwards and Rose, 1984), a few have pores or projections. Most of these cuticle sheets have been obtained from bulk maceration of rock in acid (usually hydrofluoric acid) and subsequent oxidation of the sample. Using such techniques, Edwards (1986) recovered numerous cuticles from Lower Devonian shales in Great Britain. On the inner surface of some specimens are inwardly directed flanges that may have marked the position of interior tissues. On the outer surface are projections of low relief. Because the biological affinities of these cuticles remain unknown, an artificial classification was created so that future workers would be able to correlate the various types of cuticles geographically and stratigraphically. These data may ultimately make it possible to trace the organisms in time and space once the questions of biological affinities are resolved. As paleobiologists learn more about the spatial and temporal distribution of cuticle fragments, and their macromolecular composition, the possibility of identifying which organisms produced the cuticle sheets also increases, and perhaps what evolutionary adaptations they represent.
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