Lunataspis
Lunataspis is the oldest known xiphosuran, with three known species all dating from the late Ordovician.
Discovery and species
The type species, L. aurora, was described from remains found in the Konservat-Lagerstätten deposits of the Stony [Mountain Formation], central Manitoba by David Rudkin, Graham Young and Godfrey Nolan, from fossils found in northern Manitoba, Canada in 2005. The specific name aurora is Latin for 'dawn' and is also eponymous with the mythological Roman goddess. The deposit dates from the Late Ordovician, earliest Hirnantian.A second species, L. borealis, was described in 2022 based on three specimens, including an adult and two juveniles or subadults. All specimens were found in the upper member of the Gull [River Formation] in Kingston, Ontario, dating from the latest Sandbian, late Ordovician,. This site was a warm-water platform shelf at the time near the paleo-equator.
A third species, L. gundersoni was described from two specimens found in the Big Hill Formation, which was likely a shallow lagoonal site connected to the ocean. Uniquely, this species has an elongated shovel-like prosoma with recurved posterior spines, as opposed to the more conventional form of the others. Alongside this, the holotype specimen also preserves a U-shaped structure interpreted as the ovaries, with pale spheres preserved within interpreted as eggs. This further suggests that this L. gundersoni specimen was an adult.