The fossil history of the smaller arachnid orders

Abstract The fossil record of the six living smaller arachnid orders is reviewed. Palpigradi (palpigrades) are represented by two fossil species, respectively from the mid-Cretaceous Burmese amber of Myanmar and the Pliocene Onyx Marble of the USA. Solifugae (camel spiders) are known from six unequivocal species from the Late Carboniferous Coal Measures of the USA, the Early Cretaceous Crato Formation of Brazil, the slightly younger Burmese amber, from Baltic amber (Paleogene: Eocene) and from Dominican amber (Neogene: Miocene). Ricinulei (ricinuleids), with twenty-three fossil species in total, are surprisingly diverse in Northern hemisphere Coal Measures and Cretaceous Burmese amber, but do not occur in younger ambers. Amblypygi (whip spiders) first occur unequivocally in the Coal Measures. There are thirteen fossils in total, with further records from the Crato Formation and in Burmese amber, as well as in the Indian Cambay amber (Paleogene: Eocene), Chiapas or Mexican amber (Paleogene–Neogene: Oligocene/Miocene) and the near contempary (Miocene) Dominican amber. Thelyphonida (whip scorpions) are known from fourteen species and are again found in the Coal Measures, the Crato Formation and Burmese amber, but do not occur in younger ambers. Schizomida (schizomids) are known from fourteen species; eight from Burmese amber, with additional species in Dominican amber and the Onyx Marble. The wider significance of the fossil record for the evolutionary history, morphological evolution and historical biogeography of each of these six orders, and arachnids in general, is discussed.