Cryptospores from the Hanadir Shale Member of the Qasim Formation, Ordovician (Darriwilian) of Saudi Arabia: taxonomy and systematics

Abstract

Well preserved palynomorphs from the Hanadir Shale Member of the Qasim Formation (Darriwilian) from Saudi Arabia were recovered from wells KAHF-1 and TAYM-4, which include a variety of cryptospore tetrads, dyads and monads. An assemblage of these cryptospores is described systematically for the first time. Two new cryptospore genera, Cryptotetras and Didymospora are described; one new species of Rimosotetras, R. subsphaerica, is also erected to accommodate loosely arranged tetrads comprised of sub-spherical spore-members. The palynoflora appears to have more in common with younger assemblages of latest Ordovician and earliest Silurian age than it does with problematic spore-like microfossils from older strata, indicating that these cryptospores were produced by early embryophytes, true land plants. Given the somewhat advanced evolutionary spore character of the Hanadir assemblage, the gap between the megafossil record of plant axes and spores might indicate that the plants of the Ordovician were at a bryophyte grade of evolution. The possibility remains, however, that spore characters evolved in advance of other defining characters associated with the evolution of sporophytic plant phases on land.