While collecting fossils with Alonzo W. Hancock in the Clarno Formation of Oregon in 1941, Arnold and Hancock recovered the most complete Miomastodon skull known to date.
While collecting fossils in the Clarno Formation of Oregon during 1941, noted paleobotanists Alonzo W. Hancock and Chester A. Arnold recovered the most complete Zygolophodon skull known at the time.