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Bath Royal Literary and Scientific Institution, 16-18 Queen Square, Bath BA1 2HN
Ever since the discovery of the first eurypterids, they have inspired the imaginations of both scientists and laymen. Eurypterids were truly terrifying creatures - some forms grew to over 2 m long; the largest arthropods ever to have existed. Eurypterid palaeobiology was traditionally based upon comparions with the extant horseshoe ‘crabs’ (e.g. Limulus), the only extant aquatic chelicerates, but recent research (including study of exceptionally preserved fossils and computer modelling) has revised our understanding of their respiratory, reproductory and locomotory capabilities, enabling us to ‘breath life’ into these extinct animals, and revealing important implications for their palaeoecology and phylogeny.
Eurypterid respiration has remained a mystery for over a century, but it is now known that they possessed a dual-respiratory system (i.e. four pairs of vertical gills and five pairs of “Kiemenplatten”), enabling them to undertake amphibious excursions on land. Eurypterid reproduction involved indirect spermatophore transfer via the substrate. This new view of eurypterid palaeobiology supports the the fact that they were the aquatic ancestors of the scorpions - a fact still contested by some arachnologists. Although functional studies have suggested that eurypterids used out-of-phase walking techniques, computer modelling and their fossil trackways indicate that most forms used a Limulus-like in-phase ‘swimming stroke’ style of walking; in biomechanic terms eurypterids were not well-adapted for walking on land.
Competing models of eurypterid palaeoecology, in particular the current ‘facies’ hypothesis (i.e. that eurypterids were divided into three discrete biofacies) will be critically reviewed, incorporating evidence from sedimentology and their associations. A ‘mass-moult-mate’ hypothesis is proposed, i.e. that eurypterids migrated en-masse into marginal environments to moult and mate. This is supported by abundant accumulations of eurypterid moults, the palaeobiology of eurypterid respiration and reproduction, the occurrence of abundant, sub-parallel trackways in marginal environments, and analogies with extant semi-terrestrial crabs and horseshoe crabs.
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