Calcitronidae
The family Calcitronidae is an extinct group of arachnids. Its two monotypic genera are only known from Pliocene deposits of calcite in Arizona. The family has been placed in the order Schizomida, 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 † A dagger, obelisk, or obelus is a typographical mark that usually indicates a footnote if an asterisk has already been used. The symbol is also used to indicate death (of people) or extinction (of species). It is one of the modern descendan ... Pliocene first appearances Pliocene extinctions {{paleo-arachnid-stub ...
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Schizomida
Schizomida (common name shorttailed whipscorpion) is an order of arachnids, generally less than in length. The order is not yet widely studied. About 300 species of schizomids have been described worldwide, most belonging to the Hubbardiidae family. A systematic review including a full catalogue may be found in Reddell & Cokendolpher (1995). The Schizomida is sister to the order Uropygi, the two clades together forming the Thelyphonida. Based on molecular clock dates, both orders likely originated in the late Carboniferous somewhere in the tropics of Pangea, and the Schizomida underwent substantial diversification starting in the Cretaceous. The oldest known fossils of the group are from the Mid-Cretaceous Burmese amber of Myanmar, which are assignable to the Hubbardiidae. E. O. Wilson has identified schizomids as among the "groups of organisms that desperately need experts to work on them." Taxonomy Schizom