It was just forty years ago that the writer of these lines, then an assistant of his beloved teacher, the late Professor B. F. Mudge, dug from the chalk rocks of the Great Plains his first specimens of water reptiles, mosasaurs and plesiosaurs. To the youthful collector, whose first glimpse of ancient vertebrate life had been the result of accident, these specimens opened up a new world and diverted the course of his life. They were rudely collected, after the way of those times, for modern methods were impracticable with the rifle in one hand and the pick in the other. Nor was much known in those days of these or other ancient creatures, for the science of vertebrate paleontology was yet very young. There were few students of fossil vertebrates - Leidy, Cope, and Marsh were the only ones in the United States - and but few collectors, of whom the writer alone survives.
Those broken and incomplete specimens, now preserved in the museum of Yale University, will best explain why this little book was written. The author offers it, so far as lies within him, as an authoritative and accurate account of some of the creatures of earlier ages which sought new opportunities by going down from the land into the water. So far as possible he has endeavored to make the text understandable, and, he hopes, of interest also, to the non-scientific reader. He will not apologize for such scientific terms as remain, since only by their use can precision be attained: there are no common English equivalents for them. The reader will find their explanations in the chapter on the skeleton of reptiles, and especially in the illustrations.
The author has had the opportunity during recent years of critically studying nearly all the reptiles described in the following pages, but, if that were the only source of his information, the accounts of many would have been meager. He has endeavored, briefly at least, to mention the names of all those to whom we are chiefly indebted for our knowledge, but in such a work as this it is manifestly impracticable to give due credit to every one.