On the morphospace of eurypterine sea scorpions

sSea scorpions (Eurypterida; Euchelicerata) are extinct aquatic euchelicerates with a fossil record spanning the Middle Ordovician (Darriwilian) to Late Permian (Wuchiapingian) (Lamsdell et al. 2015; Poschmann et al. 2016; Lamsdell & Selden 2017). Throughout their history, the group explored a variety of niches and palaeoenvironments, which allowed eurypterids to survive until the end-Permian extinction (Lamsdell & Selden 2017). Interpretations of their ecological roles include functioning as predators (Waterston 1964; Selden 1984; Chlupáč 1994; Braddy et al. 2008; McCoy et al. 2015; Poschmann et al. 2016; Bicknell et al. 2020), scavengers (Waterston 1979; McCoy et al. 2015; Bicknell et al. 2018; Hughes & Lamsdell 2021), and sweep-feeders (Hughes & Lamsdell 2021). This evolutionary history (Tetlie 2007; Tetlie & Briggs 2009), combined with a long record of taxonomic examination and evidence for gigantism (Braddy et al. 2008; Lamsdell & Braddy 2009) has resulted in research documenting many facets of the group. In the past, eurypterid carapace morphology has been assessed with traditional linear morphometrics (Andrews et al. 1974; Brower & Veinus 1974, 1978; Kues & Kietzke 1981; Cuggy 1994; Lamsdell & Selden 2013), with fewer studies considering aspects of the telson (Poschmann & Tetlie 2006; Ruebenstahl et al. 2021) (Table 1). There has, therefore, been no consideration of the group within a geometric morphometric context. Furthermore, no previous studies have compared morphologies of different genera (Table 1). To bring the study of eurypterids into the modern renaissance of morphological research, we therefore present a geometric morphometric analysis of landmark and semi-landmark data from eurypterid specimens across eight genera covering seven families within the sub-order Eurypterina – Carcinosomatidae, Erieopteridae, Eurypteridae, Hughmilleriidae, Pterygotidae, Strobilopteridae, and Waeringopteridae....