The mysterious Tully monster is not likely to have been a vertebrate - despite its hard cartilage ridged back - scientists claim, after discovering unusual elements within its fossilised eyes. Tullimonstrum, also known as the Tully monster, which lived 300 million years ago, has baffled scientists since fossils were first discovered 60 years ago. A previous discovery in 2016 found Tully to have a stiffened rod of cartilage that supported its body and gills - suggesting that the creatures were predatory vertebrates, similar to some primitive fish.