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NEW MATERIAL of ALAGOMYIDAE (MAMMALIA, GLIRES) from the LATE PALEOCENE SUBENG LOCALITY, INNER MONGOLIA Author(S): JIN MENG, XIJUN NI, CHUANKUI LI, K

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NEW MATERIAL of ALAGOMYIDAE (MAMMALIA, GLIRES) from the LATE PALEOCENE SUBENG LOCALITY, INNER MONGOLIA Author(S): JIN MENG, XIJUN NI, CHUANKUI LI, K NEW MATERIAL OF ALAGOMYIDAE (MAMMALIA, GLIRES) FROM THE LATE PALEOCENE SUBENG LOCALITY, INNER MONGOLIA Author(s): JIN MENG, XIJUN NI, CHUANKUI LI, K. CHRISTOPHER BEARD, DANIEL L. GEBO, YUANQING WANG, and HONGJIANG WANG Source: American Museum Novitates, :1-29. Published By: American Museum of Natural History DOI: http://dx.doi.org/10.1206/0003-0082(2007)3597[1:NMOAMG]2.0.CO;2 URL: http://www.bioone.org/doi/ full/10.1206/0003-0082%282007%293597%5B1%3ANMOAMG%5D2.0.CO %3B2 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non- commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3597, 29 pp., 15 figures, 6 tables December 12, 2007 NEW MATERIAL OF ALAGOMYIDAE (MAMMALIA, GLIRES) FROM THE LATE PALEOCENE SUBENG LOCALITY, INNER MONGOLIA JIN MENG,1 XIJUN NI,2 CHUANKUI LI,2 K. CHRISTOPHER BEARD,3 DANIEL L. GEBO,4 YUANQING WANG,2 AND HONGJIANG WANG5 ABSTRACT Newly discovered specimens of alagomyids, mostly isolated teeth collected by screenwashing at the Gashatan (Late Paleocene) Subeng locality in Inner Mongolia, document considerable intraspecific variation in Tribosphenomys minutus that has not been appreciated previously because of limited sample sizes. P4s of Tribosphenomys are described for the first time, which helps to clarify the posterior premolar identification of alagomyids. Some of the alagomyid specimens are referred to Tribosphenomys cf. T. secundus and Neimengomys qii gen. and sp. nov. Based on the new data, Tribosphenomys borealis from the Bumban Member of the Naran Bulak Formation, Mongolia, is considered to be a junior synonym of Alagomys inopinatus,andT. tertius from the Zhigden Member of the Naran Bulak Formation is regarded as a junior synonym of T. minutus. Alagomyidae, consisting of Tribosphenomys, Alagomys and Neimengomys, is maintained as a valid family. The presence of a diversity of alagomyids and other recently obtained fossils and stratigraphic evidence from the Erlian Basin suggest that the Gashatan and Bumbanian of Asia are probably correlative to the late Tiffanian– early Wasachian of North America. The faunal turnover during the Gashatan and Bumbanian in Asia is probably related to the Late Paleocene–Early Eocene global warming, but current evidence is insufficient to link any specific event with the Paleocene-Eocene Thermal Maximum. 1 Division of Paleontology, American Museum of Natural History ([email protected]). 2 Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, P.O. Box 643, Beijing 100044, China ([email protected]), ([email protected]). 3 Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Ave., Pittsburgh, PA 15213 ([email protected]). 4 Department of Anthropology, Northern Illinois University, DeKalb, IL 60115, USA ([email protected]). 5 Administration Station of Cultural Relics of Xilinguole League, Xilinhaote, Neimenggu 026000, China. Copyright E American Museum of Natural History 2007 ISSN 0003-0082 2 AMERICAN MUSEUM NOVITATES NO. 3597 INTRODUCTION Here we describe specimens of alagomyids collected by screenwashing at the Subeng Basal Glires, including mimotonids, eury- locality in the Erlian Basin of Inner Mon- mylids, stem lagomorphs, and stem rodents, golia. Some of these specimens were collected were abundant and diverse during the during the 1970s, but most were recovered by Paleocene and Eocene in Asia, suggesting that renewed fieldwork at Subeng over the past few Asia was the center of origin for this group years. (Dashzeveg and Russell, 1988; Meng et al., 2003; Asher et al., 2005). Among these early Glires, the family Alagomyidae is particularly MATERIAL AND METHODS pertinent to the origin of rodents. The family All specimens described here were collected contains the genera Tribosphenomys and by screenwashing sediment from the Subeng Alagomys, with a total of seven named species locality. A few teeth were collected in 1978, (Dashzeveg, 1990b, 2003; Meng et al., 1994; and most were obtained during the field Meng and Wyss, 1994, 2001; Tong and seasons of 2003–2004. Based on the known Dawson, 1995; Dawson and Beard, 1996; morphology of alagomyids, these isolated Lopatin and Averianov, 2004a, 2004b). teeth can be identified with a high level of These species are minuscule mammals with confidence. The specimens are housed in the gliriform, ever-growing upper and lower in- Institute of Vertebrate Paleontology and cisors typical of rodents. Their lower cheek Paleoanthropology (IVPP), Chinese Acad- teeth are rodentlike, but their upper cheek teeth are highly distinctive and less reminis- emy of Sciences, Beijing. The SEM photo- cent of those of other rodents or Glires. graphs were taken from uncoated specimens Isolated upper cheek teeth of Tribosphenomys using a Hitachi SEM machine at the American collected at the Subeng locality during the late Museum of Natural History. We follow Meng 1970s proved to be enigmatic for several and Wyss (2001) for terminology of dental decades. In an unpublished manuscript writ- features in the description. Because the dental ten by Zhai (see Russell and Zhai, 1987: 71) morphology of Tribosphenomys and Alagomys these teeth were considered to pertain to has been described in detail (Dashzeveg, a dermopteran (flying lemur) because the 1990b, 2003; Meng et al., 1994; Tong and paracone and metacone are widely separated Dawson, 1995; Meng and Wyss, 1998, 2001; by a transverse valley on the upper molars. Dawson and Beard, 1995; Lopatin and More nearly complete material of alagomyids Averianov, 2004a, 2004b; Tong and Wang, collected from the Bumban Member of the 2006), our description will be brief and Naran Bulak Formation, Mongolia (Dash- comparative, with a particular focus on in- zeveg, 1990b) and the Gashatan Bayan Ulan traspecific variation and structures that were locality in Inner Mongolia (Meng et al., 1994) previously unknown. Measurements of cheek demonstrated that these tiny mammals are teeth are taken for the maximum length and actually Glires. width. To date, three species of Alagomys have been described: Alagomys inopinatus SUBENG LOCALITY AND FAUNA (Dashzeveg, 1990a), A. oriensis (Tong and Dawson, 1995) and A. russelli (Dawson and The Upper Paleocene of central Asia was Beard, 1996). Four species of Tribosphenomys first described from the Gashato (Khashat) have been proposed: T. minutus (Meng et al., Formation in the Ulan-Nur Basin of 1994), T. borealis (Dashzeveg, 2003), T. Mongolia during the 1920s by the Central secundus, and T. tertius (Lopatin and Asiatic Expedition. Morris first studied the Averianov, 2004a, 2004b). These species range beds in 1923 (see Matthew and Granger, 1925; in age from the Gashatan to Bumbanian and Russell and Zhai, 1987: 57), and Matthew and all occur in Asia, except for A. russelli from Granger (1925) employed the term Gashato in the Clarkforkian (latest Paleocene) of North describing the Gashato fauna. The Gashato America (Dawson and Beard, 1996). Formation was formally proposed in 1927 by 2007 MENG ET AL.: NEW MATERIAL OF ALAGOMYIDS 3 Berkey and Morris. The Gashato fauna and the Institute of Vertebrate Paleontology derives from Member I of the formation, and Paleoanthropology, Chinese Academy of and is overlain by members II and III, which Sciences (Jiang, 1983; Qi, 1987; Russell and produced only one mammal taxon, Gomphos Zhai, 1987; BGMRNMAR, 1991; Meng et al., elkema (Dashzeveg, 1988). 1998). Primary fieldwork at this locality was Berkey and Morris (1927: 379) proposed the conducted by Qi Tao from the IVPP during Gashato time as an interval in the Paleocene the late 1970s and early 1980s, and the authors (their ‘‘Eocene’’). The Gashatan as an Asian of this paper have worked in the area since land-mammal age was proposed by Romer 1987. Additional investigation was also con- (1966) without definition. Szalay and ducted by the Belgian-Inner Mongolian McKenna (1971) characterized Romer’s Dinosaur project during the late 1990s. Gashatan as the joint overlapping time ranges Numerous fossils have been collected by of Palaeostylops, Pseudictops, Prionessus, and surface collecting, and over 40 tons of matrix Eurymylus. Russell and Zhai (1987: 412) from Subeng have been screenwashed by attributed the Gashato, Nomogen, Zhigden, personnel from the IVPP and its collaborators and Naran faunas, along with several other since the 1980s. Magnetostratigraphic and faunas from other parts of China, to the late paleoisotopic works have also been carried Paleocene Nongshanian (5 Nungshanian; Li out during the last few years. and Ting, 1983) Land Mammal Age of Asia, A short faunal list for Subeng (provided by
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