.|alt=An art deco–style building against a clear blue sky Rankin was hired by the University of Kansas in 1969 as an acting assistant professor of linguistics, largely based on his expertise in European languages. At the urging of his colleague, Dale Nicklas, Rankin began looking into Native American languages in the area; according to Rankin, Nicklas argued that "it was the duty of every American linguist to try to document at least one Native American language". After failing to find sufficient resources to begin a study of
Quapaw, Rankin began work on the
Kansa language in the summer of 1973, looking for the last three speakers of the language in
Shidler, Oklahoma. One of the speakers, Maude McCauley Rowe, agreed to collaborate, but refused to share stories until the winter time, in accordance with
Plains Indian tradition. Instead, Rankin recorded her recitation of the
Lord's Prayer. When he returned the next day, he brought with him a transcription and recited it back to her, shocking her. Believing her language to be unable to be written down and doomed to extinction, she requested a
photocopy of the transcription which she then disseminated throughout the tribe. Rankin and Rowe then met for two hours every weekday afternoon to record in two-week intervals. Rankin worked alongside Rowe and the two other speakers, Ralph Pepper and Walter Kekahbah, for three years, taking meticulous notes and recording dozens of hours of speech. He also compared his own notes with those of
James Owen Dorsey, an American amateur linguist and missionary who studied the language in the 1880s and 1890s. Although some of Dorsey's notes were written in
Latin to avoid
contemporary anti-obscenity laws, Rankin could read Latin. While comparing Dorsey's notes to Rowe's interpretations, he once accidentally recited a bawdy story to Rowe after failing to adequately prepare his notes that morning. He later recounted: After being granted a $40,000 fellowship by the
National Endowment for the Humanities, the project culminated in a dictionary and
grammar. Rankin eventually had to stop recording after sustaining a back injury which required surgery; his
informants died shortly thereafter, the
last speakers of the Kansa language. Rankin ultimately pursued an interest in the
Siouan languages which were spoken nearby, in part because of their endangered status. During his career, Rankin primarily focused on historical phonology of the Siouan languages, namely the
Dhegiha subfamily and the Kansa language in particular. He was also an active
lexicographer and
philologist and published works on the
Iroquoian and
Muskogean languages as well as more broadly in
archeology,
typology, and the
history of linguistics itself. Rankin later returned to Quapaw, working with its last speaker and later creating a dictionary and grammar as he had with Kansa. His outline of the
Ofo language, another Siouan language, corrected massive failures and mistakes of previous literature. At Kansas University, Rankin was promoted twice, achieving full professorship in 1986. He retired in 2005, though he continued to be involved in academia afterward. His final publication was made in 2012, entitled
: An Annotated Dictionary of Kaw (Kanza). ==Death and legacy==