[PaleoMammalogy • 2016]
Ptilocercus kylin • An Early Oligocene Fossil Demonstrates Treeshrews (Scandentia) are Slowly Evolving “Living Fossils”
Ptilocercus kylin |
Abstract
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).
DOI: 10.1038/srep18627
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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
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