All the better to see you with: eyes and claws reveal the evolution of divergent ecological roles in giant pterygotid eurypterids

Abstract

Pterygotid eurypterids have traditionally been interpreted as active, high-level, visual predators; however, recent studies of the visual system and cheliceral morphology of the pterygotid Acutiramus contradict this interpretation. Here, we report similar analyses of the pterygotids Erettopterus, Jaekelopterus and Pterygotus, and the pterygotid sister taxon Slimonia. Representative species of all these genera have more acute vision than A. cummingsi. The visual systems of Jaekelopterus rhenaniae and Pterygotus anglicus are comparable to that of modern predatory arthropods. All species of Jaekelopterus and Pterygotus have robust crushing chelicerae, morphologically distinct from the weaker slicing chelicerae of Acutiramus. Vision in Erettopterus osiliensis and Slimonia acuminata is more acute than in Acutiramus cummingsi, but not to the same degree as in modern active predators, and the morphology of the chelicerae in these genera suggests a grasping function. The pterygotids evolved with a shift in ecology from generalized feeder to specialized predator. Pterygotid eurypterids share a characteristic morphology but, although some were top predators, their ecology differs radically between genera.

Telltale eyes: the lateral visual systems of Rhenish Lower Devonian eurypterids (Arthropoda, Chelicerata) and their palaeobiological implications

“…D–E) became available in the course of this study and supplements the data of McCoy et al . (). The latter species belongs to the eurypterine clade or ‘swimming eurypterids’ with their sixth prosomal appendage modified to possess a flattened spine on podomere VI‐7 (e.g.…”

“…() and McCoy et al . () examined the lateral eyes of a number of eurypterids with respect to their visual capacities, mostly representatives of the pterygotid clade which includes the largest eurypterids.…”

The evolution of vertebrate eye size across an environmental gradient: phenotype does not predict genotype in a Trinidadian killifish

“…; McCoy et al. ). Light availability has long been viewed as an important selective force on the evolution of eyes and is associated with both increased and decreased eye size across taxa (Von Salvini‐Plawen and Mayr ; Hiller‐Adams and Case ; Fernald , b; Moser et al.…”

“…This is because eyes are an indispensable organ for the vast majority of vertebrates. In vertebrates, increases in eye size are associated with improved vision (Walls 1942;Hughes 1977;Ritland 1982;Martin 1993;Motani et al 1999;Møller and Erritzoe 2010;Land and Nilsson 2012;Caves et al 2017) and shifts in mating, foraging, and predator behavior (Huber et al 1997;Garamszegi et al 2002; Thomas et al 2006;Hall and Ross 2007;Brischoux et al 2010;Moller and Erritzoe 2010;Liu et al 2012;McCoy et al 2015). Light availability has long been viewed as an important selective force on the evolution of eyes and is associated with both increased and decreased eye size across taxa (Von Salvini-Plawen and Mayr 1977;Hiller-Adams and Case 1985;Fernald 2004a, b;Moser et al 2004;Ross and Kirk 2007;Hall 2008;Tobler et al 2008;Somanathan et al 2009;Schmitz and Wainwright 2011;Veilleux and Lewis 2011;Hall et al 2012;Martinez-Ortega et al 2014).…”

New trace fossil evidence for eurypterid swimming behaviour

“…; McCoy et al . ) and swimming aptitude (Selden ; Plotnick ). Unlike the first two traits, which have been assessed reliably from fossils, eurypterid swimming behaviour remains unresolved.…”