This research (1) reports mega-fossil evidence of Marsilea and a pollen assemblage from the same fossil bed at 24.1 Ma in the Lunpola Basin; (2) estimates the elevation of the Lunpola paleolake, central Tibetan Plateau as 2990–3690 m asl, constrained by both paleolatitude and paleotemperature corrections; (3) depicts the ecosystem around this paleolake with a temperate forest; and (4) recognizes distinct ecosystems that occurred across the plateau during the Late Oligocene. These findings provide new insight into the uplift history of the Tibetan Plateau and its ecological impacts.