Giant claw reveals the largest ever arthropod

Abstract

The fossil record has yielded various gigantic arthropods, in contrast to their diminutive proportions today. The recent discovery of a 46 cm long claw (chelicera) of the pterygotid eurypterid (‘sea scorpion’) Jaekelopterus rhenaniae , from the Early Devonian Willwerath Lagerstätte of Germany, reveals that this form attained a body length of approximately 2.5 m—almost half a metre longer than previous estimates of the group, and the largest arthropod ever to have evolved. Gigantism in Late Palaeozoic arthropods is generally attributed to elevated atmospheric oxygen levels, but while this may be applicable to Carboniferous terrestrial taxa, gigantism among aquatic taxa is much more widespread and may be attributed to other extrinsic factors, including environmental resources, predation and competition. A phylogenetic analysis of the pterygotid clade reveals that Jaekelopterus is sister-taxon to the genus Acutiramus , and is among the most derived members of the pterygotids, in contrast to earlier suggestions.

Cope's Rule and Romer's theory: patterns of diversity and gigantism in eurypterids and Palaeozoic vertebrates

“…Basal taxa in both suborders are relatively small, and more derived taxa tend to increase in size. This trend has been noted specifically in pterygotids (Braddy et al 2008a), with an increase in length of 1250 per cent, and hibbertopteroids (Lamsdell et al 2009), with an increase in length of 823 per cent. In this respect, both hibbertopteroids and pterygotids obey Cope's Rule or 'phyletic gigantism' (Gould & MacFadden 2004), yet clearly occupied different life habits; the pterygotids were nektonic predators capable of excursions into the open marine realm, while the hibbertopteroids were benthic sweep-feeders limited to freshwater environments from the Late Devonian until their extinction.…”

“…Intrinsic factors including mechanical properties of their exoskeleton and respiratory system limit maximum arthropod size, especially on land. Pterygotids had a thin, unmineralized cuticle and could attain such large size because of their light-weight construction and aquatic lifestyle (Braddy et al 2008a). Hibbertopterids adopted a more graviportal approach; their cuticle is considerably thicker and they have other adaptations linked to supporting a large body size, including grooves on the podomeres of their loadbearing legs and tubercles or ridges interpreted as muscle attachment sites on the opisthosoma, aiding the function of respiratory organs (Lamsdell et al 2009).…”

“…Such selection for gigantism is often attributed to elevated oxygen levels during the Late Palaeozoic (Berner et al 2003); however, the presence of gigantism in aquatic arthropods including Ordovician trilobites (Rudkin et al 2003), and Early Devonian eurypterids (Braddy et al 2008a) suggests that mechanisms for gigantism selection are more complex.…”

“…Most are small-medium nektonic predators (Eurypterina), and include the largest arthropods ever to have lived; gigantic pterygotids, with lengths of 250 cm estimated in Jaekelopterus (Braddy et al 2008a). Stylonurine eurypterids (Stylonurina), which have their posterior legs retained for walking, range from the Late Ordovician to the Late Permian, and also attain gargantuan proportions: Pagea, from the Early Devonian, is around 120 cm long (Plotnick & Elliott 1995) and Cyrtoctenus, from the Carboniferous, is 135 cm long (Waterston et al 1985).…”

An Evolutionary Model for the Neoproterozoic (Ediacaran)-Phanerozoic Biosphere. Part One: Concepts and Exploitation of Aquatic Environments

“…Eurypteroids were active, predaceous, benthonic animals occupying all aquatic environments and commonly reached a size of 10 -20 cm [12], although giant forms of two or more meters in length are known [13]. Eurypteroids had claw-shaped chelicerae that served for catching and crushing prey, and several pairs of oar-shaped appendages served for swimming.…”