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.
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.
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