REVISING HISTORY: A NEW TIMELINE OF DISCOVERY AT THE LAKES-MARSH “ATLANTOSAURUS BEDS” QUARRIES AT MORRISON, COLORADO

Letters sent by Arthur Lakes to O.C. Marsh spanning 1876 to 1879 have corrected the timeline of fossil discoveries in the Upper Jurassic Morrison Formation at Dinosaur Ridge (Morrison, CO). These letters clarify the “Saurian” nomenclature used by Lakes as field names given to individual specimens, not excavation site names. Examination of written documents cross-referenced with an analysis of paleontological and geological samples has refined the timeline of discovery and sorted both specimen and site.

A detailed review of the correspondence has revised the timeline of discovery at the historic Lakes-Marsh Quarries at Morrison. The correspondence includes shipping information, telegrams from O.C. Marsh, 30 letters from Lakes, 40 letters from Benjamin Mudge, and 8 letters from Samuel Williston.

Lakes’ letters to Marsh contradict the accepted timetable of discovery. Written on June 15 and 20 of 1876, two multi-page letters with illustrated diagrams by Lakes to Marsh housed in the collections at Yale University indicate the discovery of fossils in Morrison were made more than nine months prior to March 26, 1877. The latter accepted date is derived from Arthur Lakes’ “field journal” which is a collection of anecdotes written after the excavations in Morrison, CO had occurred.

Previous scholars have indicated that the nomenclature for each site shifted as the excavations were processed and consequently created phantom quarries. Lakes’ writings, however, indicate the numbered “saurians” reflect the interpretation of individual animals collected, with multiple specimens at each site. Referencing the unique lithology preserved on unprepared bone and the consequent variation in fossil permineralization, six fossil quarries were processed by the Lakes crew and are in Yale Peabody Museum collections.

This multidisciplinary approach has refined the understanding of the area where the first giant dinosaurs were found in the American West.