Habitat tracking, range dynamics and palaeoclimatic significance of Eurasian giant salamanders (Cryptobranchidae) — indications for elevated Central Asian humidity during Cenozoic global warm periods

Environmental fluctuations are a driving force in vertebrate evolution, but cryptobranchids (giant salamanders) show little morphologic change since the Jurassic. Here we analyze their fossil distribution in the Cenozoic of Eurasia and show that morphologic stasis is also maintained by stable environments, making giant salamanders an ideal proxy-group for environmental and palaeoclimatic studies. The climate space of recent and fossil cryptobranchids is best characterized by high humidity with mean annual precipitation values over 900 mm. The recorded patchiness of their fossil record can be explained by habitat tracking and/or range expansion from higher altitudes into lowland settings during humid periods with increased basinal relief. In Central Asia cryptobranchids are recorded from five intervals, four of them are global warm periods: Paleocene–Eocene Thermal Maximum, Late Oligocene warming, Miocene Climate Optimum, and Mio-Pliocene transition. This distribution suggests that during global warmth the Asian cold high pressure zone during winter months may be weak or absent, thus moist westerly winds penetrate far into the continent. The presence of cryptobranchids also indicates that the aridification across the Eocene–Oligocene boundary as reported from Mongolia and northwestern China, does not occur in the Zaysan Basin, probably due to increased upslope precipitation in the rising Altai Mountains.