As an anatomy professor at the Yale School of Medicine, Crelin noticed there was a major omission from textbooks: there were none on the anatomy of the newborn. His 1969 textbook Anatomy of the Newborn was the first to chart those waters; that, and the 1973 follow-on Functional Anatomy of the Newborn, are still the primary reference works in the field, helping improve health care in newborns.
Crelin also was fascinated by human speech. His research found that our vocal abilities developed between 500,000 years and 1 million years ago. He died June 21 at age 81.