 The same year Zallinger graduated from Yale University, he worked as a teacher in painting in Yale School of Fine Arts from 1942–1950 where he would paint his famous The Age of Reptiles.He worked as an instructor for 5 years, and then 2 more until 1950 as an assistant professor.In 1950, he went back to Seattle to work as a freelance artist and taught at Burnley School (now called The Art Institute of Seattle) for 3 years before returning to Yale again after accepting a commission by Life Magazine to create "The Age of Mammals".