ABSTRACT
Here we test the hypothesis, first suggested by L. Sprague De Camp in 1968, that “After Mesozoic reptiles became well-known, reports of sea serpents, which until then had tended towards the serpentine, began to describe the monster as more and more resembling a Mesozoic marine reptile like a plesiosaur or a mosasaur.” This statement generates a number of testable specific hypotheses, namely: 1) there was a decline in reports where the body was described as serpent or eel-like; 2) there was an increase in reports with necks (a feature of plesiosaurs) or reports that mentioned plesiosaurs; and 3) there was an increase in mosasaur-like reports. Over the last 200 years, there is indeed evidence of a decline in serpentiform sea serpent reports and an increase in the proportion of reports with necks but there is no evidence for an increase in the proportion of mosasaur-like reports. However, witnesses only began to unequivocally compare sea serpents to prehistoric reptiles in the late nineteenth century, some fifty years after the suggestion was first made by naturalists.
