Article: Intraspecific variation and relationships of some Lower Ordovician species of the dichograptid, Clonograptus

The genus Clonograptus is redefined as a form genus consisting of one phylogenetically based subgenus, Clonograptus s.s., and additional species of uncertain relationships. Clonograptus is transferred from the Anisograptidae to the Dichograptidae, since bithecae are absent along the stipes in the type species. Temnograptus, Herrmannograptus, Anthograptus, and ?Calamograptus are considered synonyms of Clonograptus s.s., based on a large fauna of 'Temnograptus' multiplex that shows extreme variation, especially in stipe length. This variation indicates that the diagnostic characters of these genera are not tenable. It also suggests that 'stipe order' is an artificial concept in clonograptids, with stipe length being instead an expression of functional morphology. The C. (C.) multiplex fauna is in part very well preserved and details of proximal morphology are described from relief specimens. A closely related but slightly older species, C. (C.) sp. aff. C. multiplex, exhibits features transitional between the families Anisograptidae and Dichograptidae, necessitating a refinement of their diagnoses. In Dichograptidae we allow a sicular bitheca, and/or stipes with a triad budding mechanism but without bithecae. As a consequence, all 'clonograptids' with bithecae along the stipes must be referred to another, anisograptid, genus. The morphology and preservation of clonograptids, and the resulting constraints on the use of statistical methods, are extensively discussed.