Maizotemnus archaeios gen. nov. sp. nov. the oldest Toxodontia (Mammalia, Panperissodactyla, Notoungulata) and the first South American mammal from the Paleocene–Eocene Thermal Maximum (Maíz Gordo formation, Salta Province, Argentina)

FERNÁNDEZ, MERCEDES; ZIMICZ, ANA N.; TROYELLI, ADRIÁN; CHORNOGUBSKY, LAURA; BOND, MARIANO; ARNAL, MICHELLE; FERNICOLA, JUAN C.

Historical Biology

Taylor & Francis

Lugar: London; Año: 2025 p. 1 - 29

0891-2963

The presence of mammals in the Maíz Gordo Formation (late Paleocene–early Eocene), SaltaProvince (Argentina) has been restricted with doubts to a single specimen, which stratigraphicorigin is also uncertain, assigned to the basal notoungulate Simpsonotus. Here, we report the firstconfidently stratigraphically controlled mammalian fossil from this unit, collected from its uppermostlevels dated at 56 Ma (Thanetian–Ypresian boundary). The specimen IBIGEO-P 143 is a poorlypreserved left maxillary fragment with M2–3 that constitutes a new notoungulate, Maizotemnusarchaeios gen. nov. sp. nov., and it represents the first South American mammal record confidentlycontemporaneous with the Paleocene–Eocene Thermal Maximum. According to the cladisticstudy, M. archaeios gen. nov. sp. nov. is closely related to the three middle Eocene ‘isotemnids’:both species of Pampatemnus (Pa. deuteros and Pa. infernalis) from Northwestern Argentina andAnisotemnus distentus from Argentine Patagonia, though no direct sister taxon was identified. Thediscovery of M. archaeios gen. nov. sp. nov. increases the diversity of basal toxodontians, expandsthe known geographic and stratigraphic distributions of Toxodontia, and represents (based ondates) the oldest record for this suborder.