Autecology of Silurian eurypterids

The autecology of eurypterids is reviewed, with particular reference to Silurian forms, and from a functional morphological standpoint. The three salinity-related ecological phases of Silurian eurypterids recognized by Kjellesvig-Waering (1961) appear to be valid and useful. Two of the four most probable eurypterid walking trails show in-phase gait patterns, suggesting they were made by animals partly or wholly out of their usual aqueous habitat. Pterygotoid and hughmillerioid eurypterids may have swum using the hydrofoil principle. Eurypteroids used the rowing principle; calculations based on this model reveal that Baltoeurypterus may have reached a maximum velocity of 2·5 x its body length per second. From the generalized eurypteroid feeding type evolved two feeding strategies: enlarged spinose limbs II and III (mixopteroids) and enlarged chelicerae (pterygotoids). Pterygotoid chelicerae appear well adapted for dealing with nektonic vertebrate prey. The 'claspers' on the anterior limbs of males of some eurypterid species may have functioned as sperm transfer organs. Knowledge of the detailed morphology ofSilurian eurypterids surpasses that ofother contemporaneous arthropods, thus far more could be known about their mode of life. I N the Silurian the eurypterids showed their greatest diversity and abundance, but Silurian eurypterid remains are of little use in detailed biostratigraphical studies because they occur most commonly in facies severely restricted in space and time. Where they do occur their importance in palaeoecological reconstructions should not be underestimated. Large and rare animals, they almost certainly occupied high trophic levels, probably as primary carnivores. Indeed, Romer (1933) suggested that Silurian eurypterids provoked the development of protective dermal armour in their vertebrate contemporaries.