By the Upper Cretaceous, most or all of the living salamander families had probably appeared. The following cladogram shows the relationships between salamander families based on the molecular analysis of Pyron and Wiens (2011). The position of the Sirenidae is disputed, but the position as sister to the Salamandroidea best fits with the molecular and fossil evidence. Genome and genetics Salamanders possess gigantic genomes, spanning the range from 14 Gb to 120 Gb (the human genome is 3.2 Gb long). The genomes of Pleurodeles waltl (20 Gb) and Ambystoma mexicanum (32 Gb) have been sequenced. In human society Myth and legend Legends have developed around the salamander over the centuries, many related to fire. This connection likely originates from the tendency of many salamanders to dwell inside rotting logs. When the log was placed into a fire, the salamander would attempt to escape, lending credence to the belief that salamanders were created from flames. The association of the salamander with fire appeared first in ancient Rome, with Pliny the Elder writing in his Natural History that "A salamander is so cold that it puts out fire on contact. It vomits from its mouth a milky liquid; if this liquid touches any part of the human body it causes all the hair to fall off, and the skin to change color and break out in a rash." The ability to put out fire is repeated by Saint Augustine in the fifth century and Isidore of Seville in the seventh century. The mythical ruler Prester John supposedly had a robe made from salamander hair; the "Emperor of India" possessed a suit made from a thousand skins; Pope Alexander III had a tunic which he valued highly and William Caxton (1481) wrote: "This Salemandre berithe wulle, of which is made cloth and gyrdles that may not brenne in the fyre." The salamander was said to be so toxic that by twining around a tree, it could poison the fruit and so kill any who ate them and by falling into a well, could kill all who drank from it. In his autobiography, Benvenuto Cellini relates: The Japanese giant salamander has been the subject of legend and artwork in Japan (e.g. the ukiyo-e work by Utagawa Kuniyoshi). The well-known Japanese mythological creature known as the kappa may be inspired by this salamander. Limb regeneration as applied to humans Salamanders' limb regeneration has long been