Taphonomy of arthropod cuticles from Pliocene lake sediments, Willershausen, Germany

University of Bristol, Department of Earth Sciences, Bristol, United Kingdom

The Pliocene lake sediments at Willershausen, Germany, have yielded a diversity of remarkably preserved fossils, including crayfish and insects. The internal structure of the cuticle of the crayfish Astacus and of insects is preserved, but shows evidence of some degradation. Chitin and amino acids survive, although the quantity that remains is variable. The proportion of chitin in the cuticle of the modern crayfish Pacifastacus (12.2%) is higher than that in Astacus from shallow depths in the Willershausen paleolake (5%), indicating that the fossils have undergone degradation. Analyses of the cuticles of these crayfish following demineralization show that some chemical components, which were presumably bound to the carbonate, are lost. The proportion of chitin (40%) in the cuticle of a weevil from the deeper part of the stratified paleolake (below the chemocline) is comparable to that in the cuticle of modern beetles. A much lower proportion of chitin (2-5%) survives in the cuticle of insects from the shallower oxygenated part of the paleolake, indicating that intensive degradation has occurred. Thus depositional setting, and biomineralization, influence the preservation of the organic constituents of fossil arthropod cuticles.

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