Oldest world Chelidae (Chelonii, Pleurodira), from the Cretaceous of Patagonia, Argentina

Four new taxa are described. Three of them are attributed to the extant Phrynops group: a primitive member, unidentified within the group or related to the large extant Phrynops forms; a primitive member of the Acanthochelys subgroup, small extant members of the group; a more evolved member, although still primitive, of the large extant Phrynops. The fourth is either a representative of an extinct group or a form related to the extant Chelus group. The presence of the second taxon in older Patagonian localities, as early as Lower Albian, indicates that the diversification of the extant groups was achieved as early as the Lower Cretaceous.