When Dr. Tolmachoff retired as curator in 1945 he was succeeded by one of his students, Mr. Eugene Rudolph (Rudy) Eller. During his 25-year tenure as curator, Eller became the first paleontologist in the United States to study the microfossils known as scolecodonts. Scolecodonts are worm jaws that, prior to Eller, had been largely ignored by paleontologists. Eller's studies attempted to utilize these worm remains for application in the new field of biostratigraphy that was being utilized by the burgeoning oil industry. Over his career, Eller published 29 articles on these microscopic fossils, always believing they would become an important tool for correlation. Eller also made collections from and published on Devonian rocks of New York, Michigan, and Ontario, and the Silurian of Wales. In 1952 Eller had the name of the section changed to Geology and Fossil Invertebrates.

In the late 1960’s Eller developed a vision problem that prompted him to first take a leave of absence and then to retire in 1970. While he was on leave, Christopher Durden, a Ph.D. student at Yale, served as the section’s curatorial assistant. Following the retirement of Eller, the section’s collections and laboratories were moved to the area that now serves as the natural history educational classrooms.