Stratigraphic distribution and suggested evolution of dendroid graptolites from the Silurian of eastern Australia

Five evolutionary lineages are proposed for Silurian species of the benthic dendroid graptolite genus Dictyonema, based largely on the exceptional eastern Australian records of the genus, comprising at least 25 species. These are: A, the delicatulum lineage with bifurcating ventral autothecal apertural spines; B, the paululum lineage with single ventral apertural spines or processes; C, the elegans lineage with isolated thecal apertures ± processes; D, the sherrardae lineage with dorsal apertural processes; and E, the venustum lineage with simple autothecal apertures. Brief comments are also made on other dendroid genera occurring in Australian strata, namely: Acanthograptus, Koremagraptus, Callograptus, Dendrograptus, Stelechocladia, Thallograptus and Palaeodictyota. Other non-graptoloid benthic hemichordates also listed are the tuboids Galaeograptus, Reticulograptus and Cyclograptus and the rhabdopleuran ?Rhabdopleura. Age ranges of all the species attributable to all of the above genera are tabulated.