Gigantoscorpio willsi is an extinct species of scorpion which lived between 345.0 million and 342.8 million years ago, during the Visean age of the Carboniferous. Its type and only specimen is BMNH In. 42706a,b, In. 42707, which is a 3D body fossil of its exoskeleton found near modern-day United Kingdom. Three other specimens (GSE 2134, GSE 2137 and GSE 2174) were previously referred to this genus, but subsequent analyses disagreed with this referral and reclassified them as indeterminate scorpions. Based on the incomplete holotype, Gigantoscorpio is initially estimated at 36.5 cm (14.4 in) or 28–42 cm (11–17 in) long, but subsequently estimated at 39–44 cm (15–17 in) long.