On the morphospace of eurypterine sea scorpions

Abstract

Eurypterids (sea scorpions) are a group of extinct, marine euchelicerates that have an extensive Palaeozoic record. Despite lacking a biomineralised exoskeleton, eurypterids are abundantly preserved within select deposits. These collections make statistical analyses comparing the morphology of different genera possible. However, eurypterid shape has not yet been documented with modern geometric morphometric tools. Here, we summarise the previous statistical assessments of eurypterid morphology and expand this research by presenting landmark and semi-landmark analyses of 115 eurypterid specimens within the suborder Eurypterina. We illustrate that lateral compound eye morphology and position drives specimen placement in morphospace and separates proposed apex predators from more generalist forms. Additionally, evidence for size clusters in Eurypterus that may reflect ontogeny is uncovered. We highlight the use of geometric morphometric analyses in supporting the naming of new taxa and demonstrate that these shape data represent a novel means of understanding inter-generic ontogenetic trajectories and uncovering developmental changes within the diverse euarthropod group.

Spines and baskets in apex predatory sea scorpions uncover unique feeding strategies using 3D-kinematics

“…The group ranged from the Lower Ordovician ( Lamsdell et al., 2015 ) until close to the end Permian ( Lamsdell and Selden, 2017 ). Across this time, the group explored different life modes, including functioning as predators ( Waterston, 1964 ; Selden, 1984 ; Chlupáč, 1994 ; Braddy et al., 2008 ; McCoy et al., 2015 ; Poschmann et al., 2016 ; Bicknell and Amati, 2021 ), scavengers ( Waterston, 1979 ; McCoy et al., 2015 ; Bicknell et al., 2018b ; Hughes and Lamsdell, 2021 ), and even sweep-feeders ( Waterston et al., 1985 ; Hughes and Lamsdell, 2021 ). Despite this range of proposed life modes, limited biomechanical or kinematic studies have been presented to support these interpretations ( Plotnick, 1985 ; Plotnick and Baumiller, 1988 ; Bicknell et al., 2021b ).…”

“…Despite this range of proposed life modes, limited biomechanical or kinematic studies have been presented to support these interpretations ( Plotnick, 1985 ; Plotnick and Baumiller, 1988 ; Bicknell et al., 2021b ). This is striking as eurypterids are occasionally exceptionally well preserved ( Holm, 1898 ; Selden, 1981 ; Braddy, 2001 ; Lamsdell et al., 2015 ; Bicknell and Amati, 2021 ) with enough anatomical information to permit three-dimensional (3D) reconstructions and modeling. Here, we present advanced reconstructions of Megalograptus ohioensis Caster and Kjellesvig-Waering (1955) (Elkhorn Formation, Late Ordovician, Ohio, USA, Megalograptidae) and Mixopterus kiaeri Størmer (1934) (Ringerike Group, Late Silurian, Norway, Mixopteridae) prosomal appendages and illustrate kinematic models that uncover facets of feeding within the two genera.…”

Description of Bothriurus mistral n. sp., the highest-dwelling Bothriurus from the western Andes (Scorpiones, Bothriuridae), using multiple morphometric approaches

“…Geometric morphometrics tools have been rarely used in scorpions. Traditionally, some authors used it to evaluate Ecomorphs (morphologies under similar ecological demands) [33,34], postembryonic stages [35] or in a paleontological way [36], being this contribution the first to use these techniques to improve a taxonomical description in the group. This is the first time that a geometric morphometric approach is applied to identify two closely related species of Bothriuridae.…”