The Fine Structure of Graptolite Periderm
Graptolites were marine colonial animals that lived in the benthos about 500 million years ago. From them planktonic automobile forms evolved, inheriting the fibrous periderm of their sessile ancestors. The great age of the fossilized periderm makes a chemical diagnosis impossible, and a transverse banding with a 70 nm periodicity (Crowther and Rickards, 1977) is the only evidence for an originally collagenous composition of the fibrils. It must also be recognized that some of the fine structure revealed by SEM could be the result of diagenesis. Nevertheless we shall describe and figure the clearest and most recurrent structures characteristic of grapto-lite periderm.
KeywordsSheet Fabric Transverse Banding Collagenous Composition Spiral Line Spiral Cord
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