Around the turn of the century, most plesiosaur research was done by a former student of Marsh, Professor Samuel Wendell Williston. In 1914, Williston published his "Water reptiles of the past and present". Despite treating sea reptiles in general, it would for many years remain the most extensive general text on plesiosaurs. In 2013, a first modern textbook was being prepared by Olivier Rieppel. During the middle of the twentieth century, the USA remained an important centre of research, mainly through the discoveries of Samuel Paul Welles.