Most orders and many families of modern mammals were established during the Palaeogene. Mammalian evolution during this period of time has been correlated with global climatic events 1-4 , although the timing, mode and scale of such a climate-evolution link remain debatable 1,5,6 . The Palaeogene global climate was steppunctuated by a warming across the Palaeocene/Eocene boundary about 55 Myr ago and a cool-off throughout the late Eocene and early Oligocene epochs 1,2,7-10 . The most severe cooling was at 33.5 Myr, slightly after the Eocene/Oligocene boundary, and was characterized by a drop in the mean annual temperature and by changes in vegetation from Eocene dense forests to Oligocene more open country 5 . Here we analyse 33 Palaeogene mammal faunas from the Mongolian Plateau of China and Mongolia. There is a distinct pattern of faunal turnovers: perissodactyl-dominant faunas of the Eocene were abruptly replaced by rodent/lagomorph-dominant faunas of the Oligocene. We interpret the turnovers as having been effected by global climatic shifts and name the prominent biotic reorganization across the Eocene/Oligocene boundary the Mongolian Remodelling, which correlates to the European Grande Coupure.Studies of the effect of climate on mammalian evolution have almost all been made in North America and Europe 2 . To study Palaeogene faunal turnovers in Central Asia and their possible relationships to climatic changes, we analysed 454 species, representing 210 genera and 88 families of mammals, from 33 local faunas in the Mongolian Plateau of China and Mongolia ( Fig. 1). Taxonomic names above the species level follow an updated classification of mammals 11 . We correlated these local faunas using a numerical clustering method (see Methods) and then converted the clustered faunas to a sequence of local mammal ages on the basis of their stratigraphic occurrences (Fig. 2). We used three radiometric datings and intercontinental faunal correlations to correlate the sequence of relative ages with the geological timescale and boundaries 12 .In all calculations the late Palaeocene and Oligocene faunas always clustered as one group, whereas the Eocene faunas may or may not form a single group (Fig. 2; Methods), indicating taxonomic differentiations among faunas of the Palaeogene epochs. We concur with placement of the Palaeocene/Eocene boundary (PEB) between the Gashatan and Bumbanian 13 but note the possibility that it may be above the Bumbanian 14 . Our reallocation of the Eocene/ Oligocene boundary (EOB) at the Houldjinian/Hsandagolian transition differs from the traditional placement of the EOB between the Sharamurunian and Ulangochuian 15,16 but agrees with the ideas of others 1,17,18 . Our method cannot differentiate Hsandagolian faunas into the biochronological subunits described in ref. 19, reflecting the faunal stability during that period of time 19 . Temporal distributions of important families show that, at the PEB, several archaic taxa (such as multituberculates) became extinct (Fig. 2), whereas Artiodactyla, Eu...
We describe several fossils referable to Gomphos elkema from deposits close to the Paleocene-Eocene boundary at Tsagan Khushu, Mongolia. Gomphos shares a suite of cranioskeletal characters with extant rabbits, hares, and pikas but retains a primitive dentition and jaw compared to its modern relatives. Phylogenetic analysis supports the position of Gomphos as a stem lagomorph and excludes Cretaceous taxa from the crown radiation of placental mammals. Our results support the hypothesis that rodents and lagomorphs radiated during the Cenozoic and diverged from other placental mammals close to the Cretaceous-Tertiary boundary.
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