''Lunataspis'' is the oldest known

xiphosura Xiphosura (; , in reference to its sword-like telson) is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Horseshoe crab, Limulidae). They fir ...

n, with three known species all dating from the late Ordovician (latest Sandbian for ''L. borealis'', Katian for ''L. gundersoni'', earliest Hirnantian for ''L. aurora'').

Discovery and species

The type species, ''L. aurora'', was described from remains found in the Konservat-Lagerstätten deposits of the

Stony Mountain Formation The Stony Mountain Formation is a stratigraphic unit of Ashgill age in the Western Canadian Sedimentary Basin. It takes the name from the community Stony Mountain, Manitoba, and was first described in the town quarry by D.B. Dowling in 1900.Dowl ...

, central

Manitoba Manitoba is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population ...

by David Rudkin, Graham Young and Godfrey Nolan, from fossils found in northern

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

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 The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

, earliest

Hirnantian The Hirnantian is the final internationally recognized stage of the Ordovician Period of the Paleozoic Era. It was of short duration, lasting about 2.1 million years, from to Ma (million years ago). The early part of the Hirnantian was char ...

. A second species, ''L. borealis'', was described in 2022 based on three specimens, including an adult (

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...

IP 64616) and two juveniles or subadults (

IP 64617 and

IP 64618). All specimens were found in the upper member of the Gull River Formation in

Kingston, Ontario Kingston is a city in Ontario, Canada, on the northeastern end of Lake Ontario. It is at the beginning of the St. Lawrence River and at the mouth of the Cataraqui River, the south end of the Rideau Canal. Kingston is near the Thousand Islands, ...

, dating from the latest

Sandbian The Sandbian is the first stage of the Upper Ordovician. It follows the Darriwilian and is succeeded by the Katian. Its lower boundary is defined as the first appearance datum of the graptolite species '' Nemagraptus gracilis'' around million ...

, 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.

References

Xiphosura Late Ordovician arthropods Ordovician animals of North America Ordovician Canada Fossil taxa described in 2008 {{paleo-arthropod-stub

Discovery and species

See also

References