The dawn of terrestrial ecosystems on Baltica: First report on land plant remains and arthropod coprolites from the Upper Silurian of Gotland, Sweden

Sporangia, with their in situ cryptospores, spore masses, and a possible axis were identified in marginal marine Ludlovian deposits from Gotland, Sweden by means of light- and scanning electron microscopy. orangia identified are elongate, with fragments of the sporangia covering preserved, and contain well-preserved in situ embryophyte cryptospores identified as Laevolancis divellomedia (monad) and Dyadospora murusdensa (dyad). A single detached axis was identified possessing superficial longitudinal striations resembling epidermal cell patterning. The axis ends in a cup-shaped structure that possibly represents the basal part of a sporangium. Masses of cryptospore monads shrouded in amorphous organic material, most probably representing coprolites of terrestrial arthropods, were found in the same beds. The spores in these masses are degraded in sharp contrast to the excellent preservation of the dispersed and sporangia-hosted spores. The monad, L. divellomedia, a common local constituent of the dispersed microflora, was identified in the coprolites. This is the first report of undisputed Silurian land plant remains in Baltica and the study reveals one of the earliest examples of arthropod–plant interactions.