low-diversity land plant fauna, dominated by giant Archaeopteris trees. The palynomorph Retispora lepidophyta was abundant in most spore zones used to define the terrestrial ecosystems of the Famennian. The major marine extinction pulse of the Hangenberg Event occurred at the boundary between the LE and LN zones, the third- and second-to-last spore zones of the Devonian, respectively. Plants were unaffected at this time. However, they started to decline near the end of the LN zone and the terrestrial ecosystem collapsed at the start of the VI zone, the last spore zone of the Devonian. This land plant extinction, which wiped out most or all of the Archaeopteris and R. lepidophyta floras, is correlated with the extinction of ‘survivor’ faunas in the latter part of the Hangenberg Event. Spore taxa that went extinct include specialized forms with divided spines (likely from an early form of lycopod) as well as widespread tiny spores (Retispora, Diducites, Rugospora) which were probably from fast-growing fern-like plants. Plants were significantly more affected by the Hangenberg event than by the Kellwasser event. Causes Anoxia The Hangenberg event was an anoxic event marked by a layer of black shale, and has been suggested to have been linked to an increase in terrestrial plant cover. That would have led to increased nutrient supply in rivers and may have led to eutrophication of semi-restricted epicontinental seas and could have stimulated algal blooms. However, support for a rapid increase in plant cover at the end of the Famennian is lacking. Global cooling Evidence such as glacial deposits in northern Brazil (near the Devonian South Pole) suggests widespread glaciation at the end of the Devonian, as a broad continental mass covered the polar region. The Hangenberg event has been associated with sea-level rise followed swiftly by glaciation-related sea-level fall, and thus a cause of the extinctions may have been an episode of severe global cooling and glaciation at the end of the Famennian, marking the dawn of the Late Palaeozoic Ice Age. Supernova One hypothesis for the cause of the last pulse of the extinction notes the abundance of malformed plant spores at the Devonian-Carboniferous boundary. This could implicate increased UV-B radiation and ozone depletion as the kill mechanism, at least for terrestrial organisms. Intense warming may lead to increased convection of water vapor in the atmosphere, reacting to inorganic chlorine compounds and producing ClO, an ozone-depleting compound. However, this mechanism has