Downloaded from rsbl.royalsocietypublishing.org on March 12, 2010 Biol. Lett. (2010) 6, 265–269 their posterior legs retained for walking, range from doi:10.1098/rsbl.2009.0700 the Late Ordovician to the Late Permian, and also Published online 14 October 2009 attain gargantuan proportions: Pagea, from the Early Palaeontology Devonian, is around 120 cm long (Plotnick & Elliott 1995) and Cyrtoctenus, from the Carboniferous, is 135 cm long (Waterston et al. 1985). A trackway from Cope’s Rule and Romer’s Scotland, attributed to Hibbertopterus, indicates an animal 160 cm long (Whyte 2005). theory: patterns of During the Devonian, the diversity of Eurypterina plummeted, whereas the hibbertopterid radiation diversity and gigantism in during the Late Devonian and Carboniferous rep- eurypterids and Palaeozoic resents the last major radiation of eurypterids. Romer (1933) proposed that eurypterids and early armoured vertebrates fish evolved in an ‘arms race’; while this theory has fallen out of favour in recent years, deemed too James C. Lamsdell* and Simon J. Braddy simplistic, it remains in text books and popular science Department of Earth Sciences, University of Bristol, Wills Memorial writing. Analysis of evolutionary trends in eurypterids Building, Queen’s Road, Bristol BS8 1RJ, UK thus provides an interesting case study to examine *Author for correspondence (
[email protected]). whether causal mechanisms for gigantism in Palaeo- Gigantism is widespread among Palaeozoic zoic arthropods, and their extinction, were primarily arthropods, yet causal mechanisms, particularly owing to abiotic (e.g. environmental) or biotic (e.g. the role of (abiotic) environmental factors versus competition between species) factors. (biotic) competition, remain unknown.