New observations on a Pridoli plant assemblage from north Xinjiang, northwest China, with comments on its evolutionary and palaeogeographical significance

Abstract

-Detailed descriptions of plant remains from a late Silurian (Pridoli) locality in Xinjiang Province, northwest China are presented. They include Junggaria spinosa Dou, interpreted as identical with Cooksonella sphaerica Senkevich, Salopella xingjiangensis Dou, and a number of sterile axes, including one with a leafy appearance superficially resembling a lycophyte, and others of probable algal affinity. Lack of anatomical and reproductive characteristics precludes a more precise assessment of relationships. A justification for the Pridoli rather than Lower Devonian age of the assemblage is based on graptolites. The composition of the assemblage is compared with coeval ones from Europe, North America, north Africa and Kazakhstan and has closest similarities with the latter. Palaeogeographic proximity on the Kazakhstan palaeocontinent is postulated, but the dearth of global Silurian occurrences of land plants make it premature to evaluate the significance of Kazakhstan and Chinese assemblages in terms of global provincialism in the late Silurian. The most distinctive element in these assemblages {Junggaria/Cooksonella) has sporangia with more complex, indeed more enigmatic organization, than seen in most Silurian and early Devonian rhyniophytoids.

Diversity and distribution of Devonian Protolepidodendrales (Lycopsida)

“…Collections from Xingxiang, northern China, probably belong with this palaeocontinent, in the same way that Pridoli assemblages from the same area are believed to originate from the Kazachstan plate (Cai et at., 1993 1983).…”

Silurian freshwater arthropod from northwest China

“…This spore assemblage was relatively common in the late Silurian strata, and very similar to that of the Utubulak Formation in the neighbouring Mangkelu area (Cai et al . 1993), the latter containing Pridoli graptolites (Ni et al . 1998).…”

Plant assemblages from the Silurian of southern Bolivia and their palaeogeographic significance

“…Other taxa e.g. C. crassiparietilis (Yurina, 1969) and Cooksonella/Junggaria (Cai et al, 1993) have relatively wider borders and differ in vegetative characters. Similarly shaped sporangia are seen in Renalia Gensel (1976), but these terminate lateral branching units of a pseudomonopodial system, a type of branching not recorded in the numerous sterile axes at Jarcas.…”

“…They were thus deposited at the same time as the initial radiation of Cooksonia recognized in the Anglo-Welsh area, the earliest record of the genus coming from the Wenlock of Ireland (Edwards & Feehan, 1980). There is no evidence for the lycophyte Baragwanathia in Bolivia although it is recorded in Australia during this time interval, nor of enigmatic 'leafy' axes and more complex rhyniophytes such as Junggaria/Cooksonella in Kazakhstfinjiang (Garratt et al, 1984;Cai et al, 1993) and those with terminal sporangia on lateral axes in Bathurst Island (Basinger et al, 1996) in securely dated Ludlow-Ridoli strata. For reviews of distribution of late Silurian assemblages see Edwards (1990) and Edwards & Wellman (2001).…”