Macro-Siouan languages
In the 19th century, Robert Latham suggested that the Siouan languages are related to the Caddoan and Iroquoian languages. In 1931, Louis Allen presented the first list of systematic correspondences between a set of 25 lexical items in Siouan and Iroquoian. In the 1960s and 1970s, Wallace Chafe further explored the link between Siouan and Caddoan languages. In the 1990s, Marianne Mithun compared the morphology and syntax of all the three families. At present, the Macro-Siouan hypothesis based on relations among Siouan, Caddoan, and Iroquoian is not universally accepted as proven.
Secoya language
The Secoya language has been classified as a member of the Tucanoan linguistic family and the sub-family, Western Tucanoan, in Ecuador and Peru. The remaining sub-families are Eastern Tucanoan and Central Tucanoan, comprising at least fourteen languages spoken in the region of the Vaupés River in Colombia and Brazil. Included among the Secoya are a number of people called Angoteros. Although their language comprises only some dialectal differences of Secoya, there are no other communicative obstacles present. The Siona of the Eno River, linguistically different from the Siona of the Putumayo, say there are significant dialectal differences between their language and Secoya, but are still considered a part of them. In ethnographic publications, the Secoya go by other alternate names as well: Encabellado, Pioje (meaning "no" in Secoya), Santa Maria, and Angutera.