342 Upper Wenlock and Ludlow Plectograptinae, Cape Phillips Fm., Canada

A rich fauna of beautifully preserved, isolated and uncompressed late Wenlock and early Ludlow retiolitids of the Subfamily Plectograptinac were recovered through acid dissolution of limestone nodules in the Cape Phillips Formation, central Arctic Islands. The fauna ranges in age from the late Wenlock Cyrtograplus lundgreni-Monograptus testis Zone to the mid-Ludlow Saetograplus fritschi linearis Zone.

Morphological characteristics of the long-ranging taxa Paraplectograptus and Plectograptus (Sokolovograptus) suggest they are the progenitors of two late Wenlock and early Ludlow subgroups: the first being those in which the virgula is attached throughout, or to some distal part of the rhabdosome; the second being those in which the virgula is free distally. Representatives of both groups ranged through to the early or mid-Ludlow. prior to the final extinction of the plectograptines.

 

Year published: 1993