Graptolites from Anticosti Island

Abstract

Summary In graptolite collection sent to Professor Lapworth near the end of the 19th century are some pieces of limestone from Anticosti Island, Canada. These form the basis of the present study, in which the structure and development of two new species of Amplexograptus and a species of Climacograptus are described from specimens preserved compressed and in relief. Much of the investigation was carried out using serial sections made with the Croft parallel grinder. The amplexograptids resemble Amplexograptus [ Climacograptus ] inuiti (Cox) but were not put into the genus Climacograptus because they possess characters relating them to Diplograptus s.l. , e.g, a high length ratio of the excavation, long interthecal septa sloping to the axis of the rhabdosome, and a sub-rectangular cross-section. The climacograptid features, e.g. a low length ratio of the excavation, interthecal septa parallel to the axis and a circular or nearly circular cross-section, are shown in Climacograptus aff. scalaris . Compressed specimens of Amplexograptus elongatus (which has very small mesial thecal flanges) show both amplexograptid and orthograptid views and an attempt is made to account for this. I. Introduction The material investigated consists of a few small pieces of limestone from Anticosti Island, Canada, included in a collection of graptolites sent to Professor Lapworth at Birmingham towards the end of the 19th century (Bulman 1950). The specimens figured here will be deposited, temporarily at least, with the Department of Geology, Birmingham University. The limestone is from the following three main localities (Twenhofel 1928, fig. 1.): Observation Cliff, North Shore; Macdonald's Cove

Uppermost Ordovician (upper Katian-Hirnantian) graptolites of north-central Nevada, U.S.A.

“…-In addition to the species included by Stewart & Mitchell, the taxon as emended here is expanded to include a number of Amplexograptus-like species with pattern K proximal structure: Amplexograptus prominens Barrass, 1954, Amplexograptus elongatus Barrass, 1954, Climacograptus latus Elles & Wood, 1908, Glyptograptus uniformis Mu & Lin (in Mu et al 1993, and Paraclimacograptus decipiens Riva, 1988. Remarks. -The genus Anticostia was established to encompass a small group of species with variously orthograptid to glyptograptid thecal profile, strong apertural lappets, a Pattern K proximal structure (Stewart & Mitchell 1997), and retaining a tightly upturned first thecal pair with a mesial spine on th1 1 similar to that in Rectograptus and Paraorthograptus.…”

Discussion of ‘Gisbornian (Caradoc) graptolites from New South Wales, Australia: systematics, biostratigraphy and evolution’ by B. Rickards, L. Sherwin and P. Williamson

“…I have collected forms that are superficially similar from close to the Eastonian-Bolindian boundary level ( Figure 2D). This form is, however, too rare (represented by about five individuals), and preservational aspect too variable, to judge its generic affiliation with any confidence; it shows some similarities with Amplexograptus prominens (Barrass 1954).…”