Upper Homerian (upper Wenlock, Silurian) graptolites from arctic Canada

Abstract

An extraordinarily well-preserved upper Homerian (uppermost Wenlock) post-extinction (post-lundgreni Event) graptolite fauna is described from Arctic Canada. The fauna of dendroids, retiolitids and monograptids, predominantly of uncompressed and isolated material, demonstrates almost totally new morphological features in comparison with the pre-extinction fauna. The two species of the lowest post-extinction fauna are followed by a rapid proliferation in the middle part of the interval, resulting in the maximum diversity, 21 species, for the entire upper Homerian. The upper Homerian is divided into three biostratigraphic units: the lower nassadubius Biozone, middle praedeubeli-deubeli Biozone, and the upper ludensis Biozone. The total fauna consists of ten species of monograptids and 11 species of retiolitids; of the latter group, three (Baculograptus, Papiliograptus and Doliograptus) are new genera, and six (B. batesi, P. papilio,P.? petilus,D. latus,Doliograptus sp. A, and Spinograptus praerobustus) are new species. Among the recognized species of monograptids, only Colonograptus schedidoneus and Lobograptus? cornuatus are confined to the Arctic, while five species of retiolitids (B. batesi,P.? petilus,D. latus,Doliograptus sp. A, and Spinograptus praerobustus) appear to be endemic.

Evolutionary history of theGothograptuslineage of the Retiolitidae (Graptolithina)

“…Two species of Baculograptus Lenz & Kozłowska-Dawidziuk, 2002 are known from the Colonograptus praedeubeli Biozone, B. chainos Lenz, 1993 andB. batesi Lenz &Kozłowska-Dawidziuk, 2002.…”

“…batesi Lenz &Kozłowska-Dawidziuk, 2002. The genus is characterized by a reticulated rhabdosome with the nema (Eisenack, 1951), ZPAL G.27/4, Baltic erratic boulder, Jarosławiec 49, Poland.…”

“…Species of Neogothograptus flourished continuously from the Col. praedeubeli Biozone up to the Lobograptus scanicus Biozone (Lenz & Kozłowska-Dawidziuk 2002;Kozłowska et al 2009). This is the first group of gothograptids with a free nema, which is a typical feature of Ludlow retiolitids.…”

“…Bates & Kirk 1984;Bates et al 2005). These walls are rarely completely preserved (Lenz & Melchin 1987;Kozłowska-Dawidziuk 1997;Lenz & Kozłowska-Dawidziuk 2002), being built from very thin and incrementally deposited fusellar layers supported by strong lists formed from bandages. Normally, therefore, only the rod-like bandaged lists of the retiolitid tubarium are preserved.…”

Internal supporting structures of some Late Ordovician graptolites from South China revealed by micro-CT

“…Important information on the structure of the graptolite tubarium has been obtained from specimens in which the original tubarium is preserved in three dimensions, whether dissolved out of siliceous or carbonate rocks (e.g. Bulman ; Kozłowski ; Urbanek ; Bates & Kirk , ; Lenz & Thorsteinsson ; Lenz & Kozlowska‐Dawidziuk ; Bates et al , ) or from serial sections (e.g. Wiman ).…”