The Crato Formation of Brazil is one of the most important localities for fossil arachnids to be found in recent years. Before its discovery there were few reliable records of spiders and their relatives throughout the entire Mesozoic era (265–248 mya) to the point that we actually knew more about the older Palaeozoic arachnid fauna; see e.g. Selden (1993) for a summary and review. Mesozoic spiders have since been found in France, Spain, southern Africa, Mexico, the USA and China (see below) – all as compression fossils in shales – as well as in various Cretaceous ambers. The Crato arachnids are generally better preserved than other records from Mesozoic shales and are in some cases easier to study than inclusions in amber. In addition to spiders, the Mesozoic record of the other arachnid orders remains patchy by comparison, but scorpions, harvestmen and mites have been described from a few localities other than the Crato Formation and our knowledge of Mesozoic arachnids is slowly improving.

The Nova Olinda Member of the Crato Formation gains its significance as an arachnid Konservat Lagerstätte through yielding the most complete fauna – with the widest range of arachnid groups (see below) – of any single Mesozoic locality known to date. The camel spider, whipspider and whipscorpion described from the Crato Formation represent the first, and so far only, record of these groups from the entire Mesozoic.