Extraordinary dimorphism in the Phyllograptid Harrisgraptus n. gen. from the early Bendigonian (Early Floian, Early Ordovician) of Victoria, Australia

Abstract

Two graptolites from the early Bendigonian (Early Floian, Early Ordovician) formerly placed in Didymograptus, D. eocaduceus Harris, 1933 and D. hemicyclus Harris, 1933, are shown to be members of a single population that shows extraordinary dimorphism. This is mainly expressed in the tubarium habit which ranges from strongly reclined to horizontal, and in stipe width which changes systematically with tubarium shape. The population is placed in the new genus Harrisgraptus and placed in the family Phyllograptidae, characterised by well-developed sicular and thecal rutella.