Cryptospores from the Hanadir Shale Member of the Qasim Formation of Saudi Arabia: a Darriwilian (Ordovician) Base for the Land Plant Spore Record

P. Strother¹, M. Vecoli², and A. Traverse³

Abstract

The stratigraphic first occurrence of land plants (Embryophyta) has long been based on the occurrence of geometrically regular (isomorphic) spore tetrads, the most widely-recognized of which are species of cryptospore genus, Tetrahedraletes. Well preserved palynomorphs from the Hanadir Shale Member of the Qasim Formation (Darriwilian) from Saudi Arabia, first recognized by Strother et al. (1996), include a variety of cryptospore tetrads, dyads and monads, which have recently been described systematically (Strother et al, in press). Our results demonstrate that the Hanadir cryptospores are more similar to younger assemblages (e.g., Silurian) than to assemblages described from Lower Ordovician and Cambrian strata. The Hanadir cryptospore tetrads are dominated by isomorphic forms, including Tetrahedraletes and a suite of newly erected taxa, which clearly demonstrate the occurrence of plant-like cell division during spore generation by Darriwilian time. This is in contrast to Dapingian (Vecoli, Beck and Strother, submitted) and Late Cambrian (Taylor and Strother, 2009) cryptospores that lack isomorphic arrangements in spore morphology. The Hanadir cryptospore tetrads now establish the Darriwilian base of land plant type spores well in advance of the Wenlock (Silurian) first occurrence of land plant megafossils. This temporal gap may be explained either by a lack of recalcitrant tissues in the earliest bryophyte-like plants or by the establishment of a “land-plant” style of simultaneous cell division in algal (streptophyte) lineages well in advance of the first true embryophytes.

AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain