It seems fitting that William John Sinclair (b. 1877, d. 1935) was born in the same year that William Berryman Scott, Henry Fairfield Osborn and Francis Speir set out on the first Princeton Scientific Expedition, for his contribution to Princeton University’s vertebrate paleontology program is no less significant.

A student of John C. Merriam at the University of California at Berkeley, Sinclair received both his M.S. and Ph.D. degrees in 1904. That same year he came to Princeton as a Fellow. His subsequent appointments included Instructor in Geology in 1905, Assistant Professor in 1916, Associate Professor in 1923, and Professor in 1930. Before coming to Princeton, he had authored several papers on a variety of subjects, including: descriptions of Protapirus robustus, a fossil tapir, and Mylagaulodon angulatus, a fossil rodent, both from Oregon; reports on the exploration of Potter Creek Cave in California; and the description of a new species of Stylemys from the Sierra Nevada of California.

In the hiatus between the loss of John Bell Hatcher to Pittsburgh and the arrival of Sinclair, Princeton’s vertebrate paleontology field collecting program continued with M.S. Farr, ably assisted by Al Silberling, leading small groups of students to Montana. Sinclair began leading expeditions in 1911 and continued to do so for several years. The focus of his collecting centered on 3 areas: the Bighorn Basin of Wyoming, the White River Badlands of South Dakota, and the Miocene and Pliocene beds of the Snake Creek region of Nebraska. He also continued to work on the mammalian cave faunas of California and the fossil faunas of the John Day River Basin of Oregon.

His 1906 paper, “Volcanic Ash in the Bridger Basin of Wyoming,” was the first to use microscopic studies to reveal the presence of volcanic ash in the sediments of the Bridger Basin. That Sinclair emphasized the interdependence of stratigraphy and paleontology can be seen in the detailed stratigraphic information that accompanied many of his taxonomic descriptions. He authored the marsupial and typothere portions of the Reports of the Princeton University Expedition to Patagonia, and with M.S. Farr co-authored the report on birds.

According to Glenn L. Jepsen, Sinclair’s student and successor, Scott spent most of his time on his own research, leaving the museum’s development and the training of graduate students in Sinclair’s capable hands. It was Sinclair who instituted and secured funding for Princeton’s William Berryman Scott Fund for research in vertebrate paleontology. He willed his own estate to the university to establish the Sinclair Professorship of Vertebrate Paleontology so that Princeton’s tradition of research and teaching in that discipline would continue.