内蒙古大庙晚中新世仓鼠科—新种(英文)

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晚中新世是古老仓鼠类型向现代属种演化的重要转折时期。描述了产自内蒙古四子王旗大庙村附近DM02地点新发现的仓鼠科化石一新种,吴氏微仓鼠Nannocricetus wuae。该种臼齿低冠,齿尖呈尖锥形;m1的下前边尖呈单尖,具有向唇、舌两侧延伸的脊,无下中脊或极微弱;m2下前小脊很退化,下中脊有或无;M1前边尖窄,轻度二分;M3长大于宽。不同于被归入Cricetodontinae的Megacricetodon和Democricetodon,新种显示出牙齿结构的简化,上臼齿无前尖刺、前中脊和内外侧的附尖,下臼齿无下前小脊刺和内外侧的附尖,上臼齿3个齿根,下臼齿2个齿根。新种在牙齿形态上与陕西蓝田灞河组发现的原始微仓鼠Nannocricetusprimitivus和内蒙古二登图的蒙古微仓鼠N.mongolicus最为接近,前者的m1下前边尖完全单尖,下前边尖与后面齿尖的连接完全缺失或极微弱,上下臼齿的中脊(下中脊)在部分标本上存在。这3个种皆为中国北部的地方类群,显示出明显的演化趋势:m1下前边尖的二分,M2/m2中脊(下中脊)的退化和前小脊(下前小脊)的发育。根据形态特征推测吴氏微仓鼠可能起源于众古仓鼠(Democricetodon),并在中国渐进演化出原始微仓鼠和蒙古微仓鼠。依据吴氏微仓鼠的进化水平,参照已有的化石记录,并结合共生哺乳动物化石,推测该地点的时代可能为晚中新世最早期。 Late Miocene is an important turning point in the evolution of ancient hamster types to modern genera. A new species of Hamster fossil, Nannocricetus wuae, found in DM02 near Diaomiao village, Siziwang Banner, Inner Mongolia, is described. The molars low crown, pointed tip was tapered; m1 under the tip of the tip was single-pointed, with lips, tongue extension of the ridge on both sides, no lower ridge or very weak; Ridge with or without; M1 apex narrow, slightly dichotomous; M3 grows wider than wide. Unlike the Megacricetodon and Democricetodon classified as Cricetodontinae, the new species showed simplified tooth structure with no premolar spikes on the upper molars, anterior midrib and medial or lateral apical appendages, no inferior premolar spine and inferior medial and lateral appendages Pointed, three molar roots on molar, two molar roots under molars. The new species was closest to N. nongolicus, a primitive hamster Nannocricetus pridivivus and a two-notched Mongolian hamster N. mongolicus in the Lantian group in Shaanxi Province of Shaanxi Province. The former was completely monophasic at the anterior apices of m1, Of the connection is completely missing or very weak, the upper and lower molars of the ridge (lower spine) in some specimens exist. All three species are endemic to the northern part of China, showing a clear evolution trend: dichotomous apical m1, degeneration of M2 / m2 mid-ridge (lower mid-vertebral ridge), and development of anterior small ridge (lower anterior ridge) . According to morphological characteristics, it is speculated that Wu hamsters may originate from ancient hamsters (Democricetodon) and gradually evolve primitive hamsters and Mongolian hamsters in China. According to the evolutionary level of Wam hamsters, referring to the existing records of fossils, combined with the symbiotic mammalian fossils, it is speculated that the site may be the earliest stage of the late Miocene.
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