Knowledge of species diversity is essential for ecological research and conservation planning, especially in overlooked ecosystems, such as the Sechura desert (SD) and the Tumbesian dry forest (DF) of Peru and Ecuador. Little is known about mammal richness in these Threatened ecosystems and thus, we quantified the richness of medium to large-sized mammals within and outside of protected areas. We used direct observation, tracks, interviews, and photographic records from 279 camera-trap locations distributed in 11 localities: three in the SD and eight in the DF. From 3839 camera-days and 56 interviews, we recorded 20 native and seven exotic species, more species than any single-locality study on these ecosystems. The most common species was Lycalopex sechurae, while the rarest species were Herpailurus yagourundi, Galictis vittata, Leopardus wiedii, and Mazama americana. We highlight southward extensions ranges for G. vittata and Lontra longicaudis and propose the southern distribution limit in the western Andes for the last four species mentioned above. We found that DF protected areas harbor higher species richness than non-protected areas but, unfortunately, up to four exotic species. These updated inventories will help direct management decisions and highlight the importance of non-protected areas as key landscapes for potential mammal connectivity.