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Geological Society, London, Special Publications; 1986; v. 20; p. 13-19;
DOI: 10.1144/GSL.SP.1986.020.01.03
© 1986 Geological Society of London

A possible new pattern of cortical deposit in Tremadoc dendroid graptolites from chert nodules

Adam Urbanek & Piotr Mierzejewski

Department of Palaeobiology (Unit for Graptolite Research), Polish Academy of Sciences, Newelska 6, 01-447 Warsaw, Poland
Museum of the Earth, Polish Academy of Sciences, A1. Na Skarpie 20/26, 00-488 Warsaw, Poland

Rhabdosome fragments of dendroids from upper Tremadoc chert nodules, studied with TEM, show an unusual pattern of cortical tissue. In contrast to previously studied tissues it consists of an irregular meshwork of wavy, branching and interconnecting fibrils. Differentiated in size and thickness, the fibrous material includes thick, strongly branched fibres. Their presence is a characteristic feature of the cortex in the dendroids examined. The observed pattern of ultrastructure is tentatively described as ‘reticulate fabric’. Its nature remains obscure. It may represent a primary feature, thus being an unusual state of aggregation of fibrous material, but its secondary origin due to preservational degradation of normal dendroid cortex seems more plausible.