Chaetocladus gracilis n. sp., a non-calcified dasycladales from the Upper Silurian of Skane, Sweden

A rare non-calcified dasycladalean alga Chaetocladus gracilis n. sp. is described from the Upper Silurian (Ludlow) Bjarsjolagard Limestone (Klinta Formation; Oved-Ramsasa Group), Skime, Sweden. C gracilis comprises a slender rod-like thallus with euspondyl, acrophorous laterals arrayed in more or less equally spaced verticils. In its morphology Chaetocladus converges on several other groups of contemporaneous flora (e.g., charalean algae, land plants) and fauna (e.g., graptolites), and the potential of misattributing dasyclads of this type to other groups such as green algae and in particular to land plants is noted and discussed. The preservation of such a delicate thallus suggests that special taphonomic conditions prevailed over parts of the Bjarsjolagard Limestone, involving rapid burial in anoxic mud and low levels of bioturbation. The presence of Chaetocladus is also indicative of an unusual floral/faunal assemblage that has been termed a 'thallophytic-alga-dominated biota'. Assemblages of this type are characterized by thallophytic algae, annelid worms, lightly sclerotized arthropods and a low diversity shelly fauna. (c) 2006 Elsevier B.V. All rights reserved.