Other mass extinctions

Neal Monks (UK) The extinctions at the Cretaceous-Tertiary (K/T) boundary make up what is probably the most famous geological event in popular culture. This is the point when the great reptiles that characterise the Mesozoic went extinct. Alongside the dinosaurs, the giant marine reptiles died out too, as did the pterosaurs, and a whole host of marine invertebrates, including the ammonites and belemnites. What happened? Some geologists argue the climate changed over a period of a million years or more, thanks to the massive volcanism that created the Deccan Traps in India. Others maintain that the K/T extinctions happened suddenly, pointing to evidence of a collision between the Earth and an asteroid. Perhaps there wasn’t a single cause, but rather a variety of factors: volcanism, climate change, asteroid impact, underlying changes in flora and fauna, and perhaps even variation in the output of the Sun and resulting weather patterns. That life on Earth can be wiped out this way is the stuff of disaster movies as much as TV documentaries. However, what comes as a surprise to many people is that there wasn’t just one mass extinction at the K/T boundary, but a whole series of them that can be observed throughout the fossil record. One of them, the Permo-Triassic extinctions, appear to have been even more catastrophic than the K/T extinctions, and at least three other extinction events are comparable in scale. In between these five big extinctions were lots of smaller extinctions that aren’t well studied, but had … Read More

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Colossal tortoises: Climate change and the evolution of Europe’s largest ‘modern’ reptiles

Benjamin Kear (Australia) and Georgios Georgalis (Greece) Most people are familiar with the famous giant tortoises of the Galapagos Islands – isolated oddities evolving in the absence of predators on a remote tropical paradise. However, as little as 5mya, continental landmasses (including Europe, Africa and India) also had their own species of giants. However, these were nearly three times the size of their modern cousins, probably close to the mass of a small car, and would have rivalled some dinosaurs for being among the most colossal reptiles of all time. Fig. 1. A life-size reconstruction of the European gigantic tortoise Cheirogaster as displayed in the University of Athens Palaeontological and Geological Museum. This model represents a massive individual of a carapace length of around 2m and was based on finds from Pikermi, near Athens, and the island of Lesvos. The best preserved gigantic tortoise fossils (as opposed to the merely ‘giant’ ones) have been found in Mediterranean Europe, particularly France, Greece and Spain, and were described in the scientific literature as early as 1877. Yet, despite an impressive chronicle of discoveries, the inter-relationships between these different kinds of gigantic tortoises are far from adequately understood. The present, albeit tentative, consensus is that there are at least three separate lineages, all of which achieved maximal body size at about the same point in geological time. Cheirogaster, the genus found in Europe, has a long fossil history stretching back some 50mys to the Eocene and includes up to 11 species. It is … Read More

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