2025/06/01 by James C. Lamsdell · 1 voice · 4 citations
Earth and Planetary Sciences · Environmental Science · #Biology #Convergent evolution #Devonian #Geology #Horseshoe (symbol) #Horseshoe crab #Ichthyology and Marine Biology #Lineage (genetic) #Living fossil #Ordovician #Paleontology #Phylogenetic tree #Subterranean biodiversity and taxonomy #Taxon #Turtle Biology and Conservation
paper · doi:10.1098/rspb.2025.0874
published in Proceedings of the Royal Society B Biological Sciences 292(2049), 20250874 (Royal Society)
openalex publication_date 2025/06/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Horseshoe crabs are an ancient lineage with an evolutionary history stretching back 450 million years and are generally considered to be examples of 'living fossils' exhibiting slow rates of evolution. Despite this reputation, relatively little is known of the early evolution of the group, with only two species described from the Ordovician and a subsequent 80-million-year gap in their fossil record until xiphosurids appear in the Late Devonian. Furthermore, all described Ordovician species are assigned to a single genus, with their close phylogenetic relatedness rendering it unclear whether their morphology is representative of the horseshoe crab ground pattern or an independently derived condition. Here, a new species of horseshoe crab is described from the Silurian of Indiana, USA. The new species bridges the temporal gap in the xiphosuran fossil record and has an overall morphology similar to that of the Ordovician taxa. These new data provide critical information on the ancestral morphology of horseshoe crabs, showing that xiphosurids evolved from forms with a fused thoracetron exhibiting axial segment boundaries, and demonstrate the persistence of basal Xiphosura into the Silurian. Laser-stimulated fluorescence is also shown to be an effective method for studying and imaging arthropod fossils exhibiting challenging preservation.