Supplemental data for: Three-dimensional kinematics of euchelicerate limbs uncover functional specialisation in eurypterid appendages

Sea scorpions (Eurypterida; Euchelicerata) explored the extreme limits of
the aquatic euchelicerate body plan. Indeed, the group contains the
largest known marine euarthropods. Inferences on eurypterid life modes—in
particular walking and eating—are commonly made by comparing the group to
horseshoe crabs (Xiphosura; Euchelicerata). However, no models have been
presented to test these hypotheses. Here, we reconstruct prosomal
appendages of two exceptionally well-preserved eurypterids Eurypterus
tetragonophthalmus and Pentecopterus decorahensis and kinematically model
the flexure and extension of these appendages in 3D. We compare these
models to 3D kinematic models of Limulus polyphemus prosomal appendages.
This comparison highlights that the examined eurypterid prosomal
appendages could not have effectively moved prey items to the gnathal
edges, and therefore would not have emulated the motion of a L. polyphemus
walking leg. It seems that these eurypterid appendages were primarily used
to walk or grab prey and other appendages would have moved prey for
mastication. Such 3D kinematic modelling highlights how eurypterid
appendage morphologies placed substantial limits on their function,
suggesting a high degree of specialisation, especially when compared to
horseshoe crabs. 3D kinematic modelling of these extinct groups also
presents an innovative approach to understanding the position of these
animals within their respective paleoecosystems.