Megarachne, a 300 million year old fossil from the Carboniferous of Argentina was described in 1980 at the world's largest spider. The idea of a huge tarantula-like spider with a body length of almost 34 cm and an estimated leg span of 50 cm caught the imagination of the public and scientists alike.
The Sedgwick Museum at the University of Cambridge has a cast of the original Megarachne fossil on permanent display alongside a full-sized model of the animal reconstructed as the world's largest spider. Researched, designed and installed by the 'Sedgwick Young Design Squad' (SYDS) in 2002, this display is popular with many of the Museum's visitors and is a fascinating glimpse into vanished worlds known only by fossils found today.
Ever since Megarachne was first described there has been controversy. Some people did not believe a spider could get so big. Others suggested it was not a spider at all. Now Megarachne has been reinterpreted by Paul Seldon (from the University of Manchester), José Corronca and Mario Hünicken (both from Argentina) as an extinct 'water scorpion' or eurypteryid, part of an extinct group that includes, for example, spiders and crabs.
The new interpretation of Megarachne, however, does not answer all of our questions. The animal still has a number of unusual features, even for a water scorpion. These questions can only be answered by the discovery of yet more fossils in Argentina.
The reinterpretation of Megarachne is a reminder of how scientific ideas change with time. Palaeontology, like many specialisms in the earth sciences, relies on making deductions about extinct animals, often on limited evidence. As more techniques become available, and as our understanding of the planet evolves, our knowledge of life on Earth will continue to be subject to reinterpretation.
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