The family Calcitronidae is an extinct group of

arachnid Arachnids are arthropods in the Class (biology), class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, opiliones, harvestmen, Solifugae, camel spiders, Amblypygi, wh ...

s. Its two monotypic genera are only known from

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

. The family has been placed in the order

Schizomida Schizomida, also known as sprickets or short-tailed whip-scorpions, is an order of arachnids, generally less than in length. The order is not yet widely studied. E. O. Wilson has identified schizomids as among the "groups of organisms that des ...

, but a review of the order concluded that "the fossil taxa ... are so poorly known that final placement must await further study and possibly new material", and they are not listed in the order in a 2016 catalog of fossil arachnids.

References

† Cenozoic arachnids † Pliocene arthropods Pliocene animals of North America Neogene arthropods of North America Prehistoric arthropod families {{paleo-arachnid-stub