Complex sentence: Goddard also points out that there is clear evidence for pre-historical contact between Eastern Algonquian and Cree-Montagnais as well as between Cheyenne and Arapaho-Gros Ventre, and that there has long been especially extensive back-and-forth influence between Cree and Ojibwe.
Split into simpler sentences: Goddard also points out that there is clear evidence for pre-historical contact between Eastern Algonquian and Cree-Montagnais, as well as between Cheyenne and Arapaho-Gros Ventre. There has long been especially extensive back-and-forth influence between Cree and Ojibwe.