Kurzfassung
Die Dicke von 100 Kopf- oder Schwanzschilden frühordovizischer Trilobiten entlang eines Küsten-Schelf-Profiles wurden in Dünnschliffen gemessen. Dabei zeigte sich, daß mit zunehmender Küstennähe die Maximaldicke der Cuticulae zunahm. Die dicksten Cuticulae sind 40mal so dick wie die dünnsten; ausschließlich dünne Cuticulae kommen nur in der küstenfernen Oleniden-Biofazies vor. Die Variationsbreite der Cuticula-Dicke nimmt küstenwärts zu. Die Cuticula-Dicke wird mehr von Umweltfaktoren bestimmt als von der Länge des Trilobiten: Einige verhältnismäßig große Trilobiten besitzen eine dünne Cuticula, und kleine Trilobiten können eine dicke Cuticula haben. Die Milieufaktoren, die das Verteilungsmuster bestimmen, werden kurz diskutiert. Die dünnen Cuticulae, die in der küstenfernen Oleniden-Biofazies dominieren, waren wahrscheinlich eine Anpassung an dysaerobe Verhältnisse. Dicke Cuticulae in der küstennächsten Biofazies boten vermutlich Schutz gegen Räuber und starke Wasserbewegung. Die Tatsache, daß dort auch Trilobiten mit einer dünneren Cuticula vorkommen, läßt sich durch die größere Verschiedenartigkeit des flachen, küstennahen Lebensraums erklären.
Abstract
100 thickness measurements from thin sections of cephala or pygidia of early Ordovician trilobites occurring across an onshore to offshore environmental gradient show that progressively greater maximum cuticle thickness was characteristic of increasingly inshore sites. There is a 40-fold difference between the thinnest and thickest cuticles, and exclusively thin cuticles are confined to the offshore Olenid Biofacies. Variability in cuticle thickness increases offshore to onshore. Environmental control is shown to be more influential on cuticle thickness than is the overall length of the trilobite: some comparatively large trilobites having thin cuticles and small trilobites thick cuticles. The environmental factors which might be responsible for the pattern are briefly discussed. The thin cuticles dominating the offshore Olenid Biofacies were probably appropriate for dysaerobic conditions. Thick cuticles in the most inshore biofacies may have offered protection against predators and turbulence, but the additional presence there of trilobites with thinner cuticles is considered to reflect the greater heterogeneity of the epeiric habitat.
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Fortey, R.A., Wilmot, N.V. Trilobite cuticle thickness in relation to palaeoenvironment. Paläontol. Z. 65, 141–151 (1991). https://doi.org/10.1007/BF02985779
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DOI: https://doi.org/10.1007/BF02985779