Caught between two mass extinctions: The rise and fall of Dicroidium

Chris Mays and Stephen McLoughlin (Sweden) In the aftermath of Earth’s greatest biotic crisis 251.9 million years ago – the end-Permian mass extinction – a group of plants arose that would come to dominate the flora of the Southern Hemisphere. Recovery of the vegetation from the end-Permian crisis was slow; but steadily, one group of seed plants, typified by the leaf fossil Dicroidium, began to diversify and fill the dominant canopy-plant niches left vacant by the demise of the Permian glossopterid forests (Fielding et al., 2019). Eventually, Dicroidium re-established a rich peat-forming vegetation across Gondwana through the Late Triassic, dominating the flora between 30°S and the South Pole (Kustatscher et al., 2018). Indeed, few fossil plant assemblages of this age can be found in Gondwana that do not contain this plant. The importance of Dicroidium is not just its role in showing biogeographic and tectonic linkages between southern lands or its value in determining the age of continental strata. Dicroidium and its associated plant groups were so successful that they were major contributors to the development of thick coal seams in the Late Triassic that are now mined to produce electricity. Although Dicroidium is generally envisaged as a plant of cool temperate climates, the very first fossils that might belong to this group are from the Permian-Triassic transition of Jordan, located near the palaeoequator (Blomenkemper et al., 2018). Nevertheless, the distribution of Dicroidium soon shifted to high southern latitudes in the Early Triassic and they overwhelmingly dominated the southern vegetation … Read More

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Wealden insects: An artist’s update (Part 4)

Biddy and Ed Jarzembowski (UK) An ‘artist’s impression’ of Wealden insects, inspired by the original work of Neil Watson, appeared in a three-part mini-series in Deposits issues 47 to 49. Since then, the discovery of a number of species new to science (belonging to diverse groups) has meant that an update was needed. Here are some completely new watercolours by Biddy, including the first true bug (heteropteran) from the Wealden, and the first Wealden earwig (dermapteran). Insects are arthropods and an accompanying Wealden crustacean is added this time. Photographs of actual fossils found in the Weald Clay Formation of Lower Cretaceous (Hauterivian and Barremian) age are provided too. We are indebted to Fred Clouter, Terry Keenan, Tony Mitchell and Pete Austen (UK) for help with these images. As before, Ed has supplied some explanatory notes to accompany the pictures, with more on the way. We have incorporated some new ideas on established species, such as different interpretations of the fossil lifestyle in the case of the ‘moss’ bug. Wealden insects are often disarticulated (due to transport in water). Where intact relatives are known from other contemporary deposits (especially Asia and Spain), these have been referred to, as well as recent representatives. While we can now recognise the commoner insect groups from the late age of the dinosaurs, continuing fieldwork shows that others remain to be unearthed. The artist’s job is ongoing, like that of the specialist and collector. We shall continue to periodically share the finds with you as a … Read More

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