Convergent Evolution Between the Mouthparts of Eurypterus lacustris and Procambarus clarkii

Abstract

Eurypterus lacustris has been reconstructed as a mid-sized detrivore and carnivore that was preserved in hypersaline shallow water environments (Nudds, 2008). Today, Red Swamp Crayfish (Procambarus clarkii) are about the same size, eat similar materials, and also live in highly variable shallow water environments (Correia, 2003). They also exhibit similar proportions in their leg segments, and have several masticating and manipulating mouthparts to aid in food processing. I argue that this similarity in trait space may indicate convergent evolution between two distantly related groups. Gnathobasids are an ancestral trait to arthropods since the Cambrian (Bicknell, 2018), however the arrangement of longer walking legs and short feeding legs (chelicerae and maxillae) seems to have evolved in both Eurypterus and Procambarus. I interpret this as a convergent adaptation to eating detritus and small bottom-dwelling animals in an aquatic environment. However, our analysis shows that Eurypterus and Procambarus mouthparts are morphologically dissimilar, and therefore do not indicate convergent evolution has occurred. I propose that size is a large driver of mouthpart selection, and discuss new techniques such as 3D reconstruction to assess convergent evolution.