Among marine Mesozoic reptiles, each of the groups broadly known as ichthyosaurs, plesiosaurs, mosasaurs and crocodiles were polyphyletic in a marked degree.

Finding plesiosaurs and ichthyosaurs through working alum shale helps to scotch the suspicion that they are merely late deposits on it.

Among marine Mesozoic reptiles, each of the groups broadly known as ichthyosaurs, plesiosaurs, mosasaurs and crocodiles were polyphyletic in a marked degree.

If Nessie truly is a cryptid of unexplained origin or a descendent of the plesiosaurs, the creature could be one of the last of its kind.