The use of experimental palaeontology in reproducing the effects of diagenetic flattening on graptolites



The detailed effects of diagenetic flattening on the graptolitc rhabdosomc have been investigated experimentally. The initial procedure, to test the effects of flattening on cylinders constructed from a variety of semi-brittle to plastic materials when compressed in a plaster ‘matrix’, demonstrates that a degree of rigidity is necessary to prevent lateral spread on diagenetic compression, even when lateral confining pressures are present. A second experiment demonstrates conclusively that the effects of flattening on the thecal style of Dicellograptus complanatus proposed by Briggs & Williams (1981; Lethaia 14) can be simulated. A model of an aseptate diplograptid produced a median depression when compressed but no preservational ‘median septum’, which is considered to be produced in several diplograptid taxa. It is shown that some diplograptids spread laterally along a median line when flattened in scalariform orientation although this has not yet been achieved experimentally owing to the high degree of compression required. □Graptolithina, diagenesis, flattening,