sentences:  It is uncertain from which of these formations the first known specimen was collected, but it may have been the Wessex Formation, where isolated "Istiodactylus" teeth have been found.The Wessex Formation consists of fluvial (associated with rivers) strata, and was deposited in a meander-belt river system which flowed from west to east and occupied the Wessex Basin.Hooley's specimens were from the Vectis Formation; these specimens are encrusted in pyrite, which is typical for fossils there.