Abstract

Benthic dendroid graptolites occur sporadically throughout the Devonian, but have no biostratigraphic significance. The planktonic Graptoloidea are confined to the Lower Devonian (Gedinnian to lower Emsian; Lochkovian to topmost Pragian; Zlichovian). They are of outstanding value for worldwide correlations, faunas being uniformly composed of cosmopolitan species. The following eight to nine Lower Devonian graptolite zones are distinguished (in ascending order): Monograptus uniformis, M. praehercynicus, M. hercynicus, M. falcarius, M. kayseri, M. fanicus (this is supposed to be in part or all correlative with the kayseri Zone), M. thomasi (with lower and upper subzone), M. yukonensis, and M. pacificus; the zonation above the hercynicus Zone is in part tentative. All continents, except South America and Antarctica, have yielded Devonian graptoloids. Some 30 species and subspecies are recognized and assigned to 4 genera: Monograptus (almost 30), Linograptus (1); Abiesgraptus (at least 3), and Climacograptus (single rhabdosome from the Carnic Alps, Austria). The Monograptus species are small to medium sized, typically with 20 to 40 thecae in the straight to moderately curved, robust rhabdosome. Thecae are of the type of M. uncinatus, at least proximally, often becoming simpler distally. The giant Linograptus and Abiesgraptus that house up to several thousand zooids are confined to the Lochkovian (Gedinnian).