Discovery of a Late Miocene Mammalian Fauna from Siziwang Banner, Inner Mongolia, and Its Paleozoogeographical Significance

Article Geology February 2011 Vol.56 No.6: 526–534 doi: 10.1007/s11434-010-4259-0 SPECIAL TOPICS: Discovery of a Late Miocene mammalian fauna from Siziwang Banner, Inner Mongolia, and its paleozoogeographical significance DENG Tao1*, LIANG Zhong1,2, WANG ShiQi1, HOU SuKuan1,3 & LI Qiang1 1 Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; 2 China Geological Library, Beijing 100083, China; 3 Graduate University of the Chinese Academy of Sciences, Beijing 100049, China Received May 10, 2010; accepted October 27, 2010 The Wulanhua Fauna (~7 Ma) derives from the basal part of Late Miocene red clays in Siziwang Banner, Inner Mongolia. Chi- nese red clay deposits are rich in fossils of the Hipparion fauna, and are relatively widely distributed across Shanxi, Shaanxi, He- nan, and Gansu provinces. The Mongolian Plateau also contains well-developed Neogene deposits, especially in central Inner Mongolia, where a sequence of mammalian faunas has been identified. The discovery of the Wulanhua Fauna provides an important indicator of the paleogeographical distribution of the Hipparion fauna, and this study also contributes to a better understand- ing of the climatic and environmental significance of red clays. Most forms of the Wulanhua Fauna are the same as or close to taxa within the Baode Fauna. However, some forms are slightly more derived than those of the Baode Fauna, which may indicate a slightly younger geological age of about 7 Ma. The components of the Wulanhua Fauna suggest that the habitat was a typical steppe and therefore yield direct evidence to delineate the boundary between the east and west subregions of the Late Miocene Hipparion fauna in North China. Siziwang Banner, Inner Mongolia, Late Miocene, red clay, mammal, zoogeography Citation: Deng T, Liang Z, Wang S Q, et al. Discovery of a Late Miocene mammalian fauna from Siziwang Banner, Inner Mongolia, and its paleozoogeographical significance. Chinese Sci Bull, 2011, 56: 526−534, doi: 10.1007/s11434-010-4259-0 The central Inner Mongolia area, including Xilin Gol dant species within the specimens recovered. Late Miocene League and part of the region around Ulan Qab City is rich Hipparion fossil localities are numerous in China, espe- in Neogene mammalian fossils, especially shovel-tusked cially in the red clay deposits in northwestern China. Con- elephants of the classical Tunggur tableland and micro- versely, fossil localities of the Hipparion fauna are com- mammals of the Ertemte locality, which have been paratively infrequent in eastern China, and generally are well-known for many years [1,2]. On the other hand, until preserved in fluvial sandstones or lacustrine marlites. Thus, now only a few mammals have been found in the Late their sedimentary environments are distinctly different from Miocene red clays of this region, which are similar to the those in northwestern China. The Chinese Miocene mam- Hipparion Red Clay fauna in North China. Recently, a sig- malian faunas differ in a west-east direction, which is con- nificant number of mammalian fossils were discovered at a sistent with geographical patterns of the area. In addition, red clay exposure south of Wulanhua Town, Siziwang similar evidence has been described for the Early Miocene in Banner (Figure 1). The excavated fossils and their taphon- previous studies [3]. However, it still is unclear as to whether omy indicate that they belonged to the Late Miocene Hip- these differences existed during the Late Miocene, and parion fauna. Chilotherium anderssoni was the most abun- where exactly was the paleozoogeographical boundary situated between the east and west regions. These questions have *Corresponding author (email: [email protected]) been the focus of interest for Chinese Neogene researchers. © The Author(s) 2011. This article is published with open access at Springerlink.com csb.scichina.com www.springer.com/scp Deng T, et al. Chinese Sci Bull February (2011) Vol.56 No.6 527 [5–8]. This locality was found in the 1920s, at which point the Austrian paleontologist O. Zdansky began to organize systematic and scientific excavations from 1922 onward. A large number of specimens were collected from Baode, including many well-preserved skulls and teeth that represent at least 57 species of large mammals [9], with a geological age of 7.2 Ma [10,11]. Most fossil members of the Hip- parion fauna collected from Wulanhua are very similar to those of the Baode Fauna. The stratigraphy and paleontology of the Wulanhua locality are reported herein in order to add to the Neogene sequence of mammalian faunas in central Inner Mongolia, and to provide important evidence to determine the boundary between the Late Miocene mammalian east-west subregions in North China. 1 Stratigraphy Nanliang is located at 3 km south to Wulanhua Town, Sizi- wang Banner, Ulan Qab City, Inner Mongolia Autonomous Figure 1 Geographical location of the Wulanhua fossil locality in Sizi- Region (Figure 1). The fossil locality is situated 250 m west wang Banner. of the Hohhot-Xilinhot highway (Provincial highway 101). Fossils are concentrated in the quarry of the Nanliang brick factory and in the middle part of the south slope of a small The red clay deposits of Siziwang Banner are located rela- hill. Clay digging formed a 3 meter-high escarpment of red tively eastward in China, and the fossil locality of the Hip- clays, in front of which fossils are concentrated on a flat parion Red Clay at Wulanhua is to the north in China. The area (41°29′45.4′′N, 111°41′31.1′′E, elevation of 1490 m). particular geographical position of this locality provides an Two pits have been excavated scientifically, with a large opportunity to answer some of the questions mentioned number of mammalian fossils preserved in situ. In addition, above. In recent years, we have investigated the Wulanhua some fossils have been found in the red clay escarpment. A fossil locality with regard to its in situ taphonomy, and we new anchithere species, Sinohippus robustus, was reported have identified the excavated and collected fossils. Our from this locality [12]. The slope behind the escarpment is work demonstrates that these mammalian fossils derived covered by grass, on which an artificial section was dug to mainly from the basal part of the red clay exposure at this expose the Late Miocene red clay deposits. This section locality. This section has a thickness of about 23 m (Figure starts from the lowest point of the fossil pit, and ends at the 2) and includes a new rodent species in its lower part. Based top of the hill, with a total thickness of about 23 m (Figure on the fossil assemblage, the age of the Wulanhua Fauna is 2). The entire section consists of red clays, intercalated with slightly later than that of the Baode Fauna. some marlite bands, and its base is not exposed. This sec- Across North China, fossil localities with rich mammals tion is described from top to bottom as follows: from Late Miocene red clays are relatively numerous [4], Quaternary especially in Baode (Shanxi), Fugu (Shaanxi), Xin’an (He- 15 Late Pleistocene loess and modern soil ~0.5 m nan), and Linxia (Gansu). Among them, the most famous ~~~~~~~~~~Disconformity~~~~~~~~~ and first discovered locality is Baode in Shanxi Province Upper Miocene 14 Yellowish-brown marlites indurated by cement, with high density and abundant iron-manganese growths (< 1 mm diameter). Miarolitic pores and fissures are abundant (< 1 mm diameter). 1.2 m thick. 13 Brownish-red muddy siltstones, poorly cemented. Cal- careous deposits occur in some fissures. This layer contains white calcareous muddy granules (up to 7 mm diameter). Small black granules of metamorphic rocks are infrequent (4 mm diameter). 1.15 m thick. 12 Purplish-red calcareous nodules, irregular in shape. They are angular blocks (15–20 cm average diameter) with calcareous cement. Fissures and pores are abundant, in which there are Figure 2 Stratigraphic section of the Wulanhua fossil locality in Sizi- white calcareous coatings. Small miarolitic cavities (1 mm wang Banner. diameter) are numerous. Glaebule structures occur inside the 528 Deng T, et al. Chinese Sci Bull February (2011) Vol.56 No.6 calcareous blocks. Occasional plant roots also found. sional thinly layered marlites or conglomerates. The known 5.08 m thick. mammalian fossils from the Wulantuke Formation include 11 Purplish-red calcareous silty mudstones with dense ce- Ochotona sp., Sinohippus zitteli, Hipparion sp., Chilother- ments. Concentrated occurrences of iron-manganese grains ium sp., Cervus sp., and Gazella sp. [14]. and white calcareous grains have diameters smaller than 1 mm. Uncommon calcareous micolitic pores also occur, with diameters of about 0.5 mm. 0.44 m thick 2 Mammalian fossils 10 A paleosol of poorly cemented, purplish-red silty mudstones shows pedogenic crumb-structures, containing a great number of white angular marlite granules to 10 mm The following is the identification list of the known mam- diameter. 1.4 m thick. malian fossils collected from the Wulanhua locality: 9 Yellowish-brown marlites indurated by dense cement. Brachyscirtetes sp. nov., Hyaenictitherium sp., Machairodus There are many small miarolitic pores (< 1 mm diameter), sp., Sinohippus robustus, Hipparion teilhardi, H. platyodus, some of which connect with one another to form irregular Chilotherium anderssoni, Cervavitus novorossiae, Palaeo- tube networks. 0.52 m thick. 8 Light brownish-red silty mudstones with dense calcareous tragus microdon, Samotherium sinense, Gazella gaudryi, cement. There are calcareous miarolitic pores (< 1 mm Plesiaddax depereti, and ?Tragoreas palaeosinensis. diameter), and occasional white calcareous grains (3 mm Most of the above-mentioned mammals are the same as diameter). 0.95 m thick. or close to the members of the Baode Fauna, such as 7 Yellowish-brown marlites, containing abundant silt-sized Machairodus sp., Chilotherium anderssoni, Cervavitus no- grains, with dense cementation, low density, and white vorossiae, Palaeotragus microdon, Samotherium sinense, miarolitic pores (1 mm diameter).

Load more