A provisional classification of the graptolite Order Dendroidea

It is argued that a morphological, stratigraphical and evolutionary series can be established in the Middle and Upper Cambrian for the origin and early diversification of the graptolite Order Dendroidea, the main benthic order of the class Graptolithina. Rhabdosomal form is shown to be useful in classification down to generic level, and it is considered thatDendrograptus gave rise through more ordered species, sequentially toCallograptus andDictyonema;Desmograptus;Aspidograptus andAcanthograptus; and then to compoundAcanthograptus, Thallograptus andPalaeodictyota. Thus by the Upper Cambrian all the main genera of the families Dendrograptidae and Acanthograptidae were established. The latter family then became dominated by genera with compound stipes; whilst a minority of compound genera arose in the Dendrograptidae such asPseudocallograptus Skevington 1963; some groups deriving from the Dendrograptidae are separated as distinct families, namely the Pseudodictyonemidae and the Stelechocladiidae (Chapman et al. 1993).