Article: Implications of normal and abnormal growth structures in a Scottish Silurian dendroid graptolite

Normal growth patterns and structure of one species of dendroid, Dictyonema pentlandica, from the North Esk Inlier, Pentland Hills, Lothian, UK, are described and considered to be the result of the secretory zooids adhering to a strict and characteristic growth pattern. Aberrant and abnormal structures include: stipe truncation and compensatory growth by neighbouring stipes; changes in growth pattern; abnormal bursts of growth; tearing or splitting; and abnormal thecal growth. The possible causes of these abnormalities are considered to be the result of mutation, injury or trauma, disease and/or parasites, environmental-change, and preservation. Dendroids could repair their rhabdosomes after damage, the nature of the repair being dependent on where the injury had taken place. It is suggested that more palaeoenvironmental and palaeoecological data could be obtained by the recognition of aberrant features in other animal groups.