The zedrosis is found in some medieval encyclopedias. It is a sea monster that is so large its bones can be cut down to make the doors of houses and palaces.

Thomas of Cantimpré's name for this animal is a misunderstanding of the account in Pliny the Elder (Book 9, 2) where he says "the Gedrosi who live by the river Arabis make the doorways in their houses out of the monsters' jaws and use their bones for roof-beams." Thomas turned the name of a group of people, Gedrosi in the name of an animal, zedrosi. The beast is probably intended to be some sort of cetacean.