New insights into the aquatic microfauna of the Lower Devonian Rhynie and Windyfield chert: an old ecosystem revisited

Investigating ecosystems of the past is understandably different from studying modern-day ones. Many properties of now-gone ecosystems can only be indirectly inferred, where in modern ecosystems observations or measurements would provide a direct access (though being less easy for hardly accessible ecosystems, e.g. in the deep sea). Indirect access to fossil ecosystems is provided by the life habits of the extinct organisms that have been living in these ecosystems, such as aspects of their feeding behaviour or their life history strategies. The life habits of an extinct organism can finally be inferred by reconstructing the functional morphology, based on the morphological details observed in fossils in comparison to modern counterparts. Such investigations gain precision when exceptionally well-preserved fossils are studied, like those of the Lower Devonian Rhynie and Windyfield chert. These deposits preserve a diverse range of representatives of Euarthropoda, partly with terrestrial, partly with aquatic, non-marine lifestyle. Among aquatic forms, especially crustacean fossils have become known, such as the famous Lepidocaris rhyniensis. The preservation of the crustacean fossils provides details of their feeding apparatus down to the sub-micron-range, including different types of setal structures. Based on these observations, we can infer that crustaceans in the Rhynie and Windyfield chert performed a variety of different life habits. The biota thus contained a rich and differentiated non-marine aquatic fauna already 400 million years ago.