|Ptilocercus kylin |
Li & Ni, 2016
Treeshrews are widely considered a “living model” of an ancestral primate, and have long been called “living fossils”. Actual fossils of treeshrews, however, are extremely rare. We report a new fossil species of Ptilocercus treeshrew recovered from the early Oligocene (~34 Ma) of China that represents the oldest definitive fossil record of the crown group of treeshrews and nearly doubles the temporal length of their fossil record. The fossil species is strikingly similar to the living Ptilocercus lowii, a species generally recognized as the most plesiomorphic extant treeshrew. It demonstrates that Ptilocercus treeshrews have undergone little evolutionary change in their morphology since the early Oligocene. Morphological comparisons and phylogenetic analysis support the long-standing idea that Ptilocercus treeshrews are morphologically conservative and have probably retained many characters present in the common stock that gave rise to archontans, which include primates, flying lemurs, plesiadapiforms and treeshrews. This discovery provides an exceptional example of slow morphological evolution in a mammalian group over a period of 34 million years. The persistent and stable tropical environment in Southeast Asia through the Cenozoic likely played a critical role in the survival of such a morphologically conservative lineage.
Ptilocercus kylin sp. nov.
Etymology: Specific epithet is derived from the name of Qilin District, in Qujing City. Qilin is the pinyin for kylin, a hoofed dragon-like beast of Chinese myth.
Holotype: IVPP V20696 (Fig. 1), a right mandibular fragment preserving m2 and m3.
Locality and horizon: Lijiawa Mammalian Fossil locality, Yunnan Province, China. Earliest Oligocene, ~ 34 Ma.
|Figure 3: Summary phylogeny of treeshrews.|
|Figure 4: Ptilocercus treeshrew distribution in the context of southern Asia’s modern geography and early Oligocene palaeogeography. |
(A) Fossil locality of Ptilocercus kylin sp. nov. (blue dot) and the distribution of the living species Ptilocercus lowii (pale reddish shading). The background map is from: wikimedia.org (under the Creative Commons Share Alike license: creativecommons.org). (B) Fossil locality (blue dot) and reconstructed palaeogeographic distribution of the closed canopy of tropical rain forest and monsoonal forest (pale reddish shading) in the early Oligocene. The palaeogeographic reconstruction is from ref. 46 (Nature Publishing Group License: 3646200322068). The position of the fossil locality on the palaeogeographic reconstruction was estimated based on its distance from the Tibetan Plateau and the Sino-Burman Ranges (SBR).
Qiang Li and Xijun Ni. 2016. An Early Oligocene Fossil Demonstrates Treeshrews are Slowly Evolving “Living Fossils”. Scientific Reports. 6; 18627. DOI: 10.1038/srep18627
Earliest-known treeshrew fossil found in Yunnan, China
http://phy.so/373022526 via @physorg_com