More than 1200 spider species are known from fossils. A Devonian fossil described as a spider has been reinterpreted as belonging to another arachnid group. Thus, the earliest evidence of spiders come from Carboniferous fossils resembling Mesothelae. Records of the Opisthothelae appear during the Triassic.
Fossils from the lower Cretaceous periods suggest that the orb web is around 130 million years old. There is little indication that spiders suffered major extinctions at the end of the Cretaceous.