Lower Devonian graptolites from southeastern Alaska

Abstract

The youngest zones of Monograptus occur in Devonian black shale and slate along the western shore of Prince of Wales Island and on Noyes Island, southeastern Alaska. The following five species of Monograptus , in close association with vascular plants and marine shelly faunas, indicate a Praguian, (Siegenian to Early Emsian), late Lower Devonian and possibly early Middle Devonian age: M. yukonensis Jackson & Lenz, M. n. sp. aff. yukonensis ? Jaeger & Stein, M. aeqimbilis notoaequakilis Jaeger & Stein, M. pacificus Jaeger n. sp. and M. craigensis Jaeger n. sp. The yukonensis zone containing M. craigensis in its upper part is followed stratigraphically higher by the M. pacificus zone – the youngest occurrence of Monograptus. The new species belong to the M. uncinatus group and, like most Praguian monograptids, have long dorsal tongues on their siculae. M. craigensis and M. pacificus increase to seven the number of species of Monograptus known from the Praguian. On the basis of the Alaskan material, the geographical distribution of M. aequabilis notoaequabilis now includes North America in addition to previously recorded occurrences in Australia, Southeast Asia, and Europe. This broad geographic distribution suggests that the last survivors of Monograptus had worldwide distribution and a rather uniform assemblage of species.