HISTORICAL BIOLOGY, 2016 http://dx.doi.org/10.1080/08912963.2016.1232406 New dipodid rodents from the Late Eocene of Erden Obo (Nei Mongol, China) Qian Lia, Yan-Xin Gonga,b and Yuan-Qing Wanga aKey Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China; bUniversity of the Chinese Academy of Sciences, Beijing, China ABSTRACT ARTICLE HISTORY New dipodid occurrences (Heosminthus nomogenesis sp. nov., Sinosminthus sp., Allosminthus cf. A. Received 23 July 2016 majusculus, Allosminthus ernos and Allosminthus cf. A. diconjugatus) are reported from the ‘Upper Red’ Accepted 31 August 2016 beds of the Erden Obo section in Nei Mongol, China. Heosminthus nomogenesis is similar to Heosminthus KEYWORDS primiveris from the Caijiachong Formation, and it is more primitive than Heosminthus chimidae of the Mammalia; dipodid; Eocene; Mongolian biozone A. Allosminthus cf. A. majusculus has a more variable mesolophid and metalophid in Nei Mongol; Erden Obo m1-2. Based on the dipodid assemblage, the age of the ‘Upper Red’ of the Erden Obo section is late Eocene and correlative to the Ergilian. Based on the comparison of their morphological characters, we recognize some differences between the stem dipodoids and muroids. Introduction ‘Upper Red’ bed is reddish muddy fine sandstone with some The earliest fossil record of the Dipodoidea is the Late Early calcareous nodules; the middle part is primarily red mudstone, Eocene or Middle Eocene in Asia and North American with bands of white fine sandstone and nodules; and the upper (Shevyreva 1984; Emry & Korth 1989; Dawson et al. 1990; Wang part is brownish red mudstone. All dipodid specimens reported & Dawson 1994; Tong 1997; Emry, Tyutkova et al. 1998; Emry here were collected via surface prospection and screenwashing 2007). Rich deposits of Dipodidae have been discovered from the from the ‘Upper Red’ beds, but at slightly different spots. Oligocene and Miocene in Asia (Wang 1985; Huang 1992; Emry, There are four dipodid genera known from the Middle and Lucas et al. 1998; Wang & Qiu 2000; Wang et al. 2003; Ye et al. Late Eocene of China. These are Allosminthus, Heosminthus, 2003; Bendukidze et al. 2009). In Europe and North American, Sinosminthus (Tong 1997; Wang 1985, 2008; Daxner-Höck the dipodid appeared later, and the earliest representatives were et al. 2014),and Priminsminthus (Tong 1997). Among these, collected in Late Oligocene deposits (Daxner-Höck & Wu 2003; Priminsminthus exhibits the most primitive character array for Flynn 2008; Zhang et al. 2013). the group. Allosminthus and Heosminthus are still earlier dipo- The dipodid specimens reported here came from the dids appearing in the Late Eocene of Central Asia. ‘Upper Red’ beds of Erden Obo (Urtyn Obo), Nomogen Sumu, The new material described here adds important data on Siziwangqi, Nei Mongol, China. Osborn (1929) first reported the dental morphology of Allosminthus and Heosminthus. The the Erden Obo section based on Granger’s and Spock’s field discovery not only expands the geographic distribution of the notes. He subdivided the deposits in the section into 8 units, late Eocene dipodids in Asia and increases the assemblage of termed in descending order as the ‘Upper White’, the ‘Upper fauna from the ‘Upper Red’ of Erden Obo, but also helps for Red’, the ‘Middle White or Gray’, the ‘Middle Red’, the ‘Lower stratigraphic correlation and determining the ages of fossilif- White’, the ‘Lower Red’, the ‘Basal White’, and the ‘Basal Red’. erous beds. These units were later referred to as the ‘Baron Sog Formation’, the ‘Ulan Gochu Formation’, the ‘Shara Murun Formation’ and Material and methods the ‘Arshanto? Formation’. Later, Chang (1931), Pei et al. (1963) and other researchers (Jiang 1983; Qi 1990; Qiu & Wang 2007) All newly described specimens were collected in several field divided the strata into different stratigraphic formations and expeditions during 2007–2012 by a joint team from the Institute ages. Because of the complicated research history and potential of Vertebrate Paleontology and Paleoanthropology (IVPP), sedimentary hiatuses in the sequence, the formal division and American Museum of Natural History, Carnegie Museum of correlation, including naming of the stratigraphic units, has yet Natural History and Northern Illinois University. Dental termi- to be completed (Wang et al. 2012). For the present, we continue nology in the description illustrated in Figure 1, was modified to use the descriptive term ‘Upper Red’ of Osborn to denote the from Wang (1985) and Daxner-Höck et al. (2014). Measurements beds yielding the fossils reported here. The lower part of the of teeth were taken using a reticle with an accuracy of 0.1 mm CONTACT Qian Li [email protected] © 2016 Informa UK Limited, trading as Taylor & Francis Group 2 Q. LI ET al. Figure 1. Terminology used in this paper to described molars, modified from Wang (1985) and Daxner-Höck et al. (2014). Notes: (a) upper molar: 1. paracone; 2. mesostyle; 3. mesoloph; 4. metacone; 5. metaloph; 6. posteroloph; 7. hypocone; 8. mesocone; 9. entoloph; 10. sinus; 11. protocone; 12. anterior cingulum; 13. protoloph II; 14. anterior arm of protocone; 15. lingual anteroloph; 16. anterolophule; 17. protoloph I; 18. labial anteroloph. (b) lower molar: 1. metaconid; 2. posterior arm of protoconid; 3. mesolophid; 4. entoconid; 5. hypolophid; 6. hypoconulid; 7. posterolophid; 8. hypoconid; 9. ectolophid; 10. mesoconid; 11. protoconid; 12. anteroconid; 13. mesostylid; 14. ectomesolophid; 15. ectostylid; 16. labial anterolophid; 17. anterior arm of protoconid; 18. metalophid; 19. lingual anterolophid. mounted in an Olympus SZX7 microscope. SEM photographs mesoloph of M1-3 long or of medium length; anteroconid of m1 of coated teeth were taken using a JSM-6100 SEM machine present; posterior arm of the protoconid extended to metaconid; at the Key Laboratory of Vertebrate Evolution and Human mesolophid of m1-2 long. Origins of Chinese Academy of Sciences, Institute of Vertebrate Differential diagnosis: Heosminthus nomogenesis differs from Paleontology and Paleoanthropology, Chinese Academy of H. primiveris in being larger and having a complete protoloph II Sciences. of M2, shorter mesoloph on M3, weaker mesostylid and hypoco- nulid on m1-2. It differs from H. borrae in being larger, having Systematic Paleontology more robust cones, lower crests and wider sinus, having a pro- toloph II on M2 and a strong posterior arm of the protoconid of Rodentia Bowdich, 1821 m2. It differs from H. chimidae in having shorter anterior arm of Dipodoidea Fischer de Waldheim, 1817 the protocone on M1, and weaker anteroconid, mesoconid and Dipodidae Fischer de Waldheim, 1817 hypoconulid on lower molars. Sicistinae Allen, 1901 Etymology: The specific name is derived from Nomogen, the Heosminthus Wang, 1985 type locality of the species. Heosminthus nomogenesis sp. nov. Holotype: IVPP V 17810, right maxilla with M1-3. Description Referred specimens: IVPP V 17811.1-2, right M1; V 17811.3-4, left M2; V 17811.5-7, left m1; V 17811.8-9, right m1; V 17811.10, M1 is trapezoidal in outline, and is slightly wider posteriorly than left m2; V 17811.11-12, right m2. anteriorly. The contact facet on the anterior surface is consistent Locality and Horizon: Erden Obo, Nomogen, Siziwangqi, Nei with presence of a small P4. The four main cones are robust Mongol; lower and middle part of the ‘Upper Red’ beds. in opposed position. The short anterior arm of the protocone Diagnosis: small-sized species; four main robust cusps; lophs neither reaches to the anterolabial edge of the tooth, nor joins short and lower than cusps; short anterior arm of protocone the paracone, from which it is separated by a shallow groove of M1 and paracone separated by a shallow groove; M1-2 with (Figure 2(a) and (b)). The protoloph II is complete and connects protoloph II; metaloph of M1-3 continuous with hypocone; with the posterior arm of the protocone. The metaloph joins the HISTORIcal BIology 3 Figure 2. Cheek teeth of Heosminthus nomogenesis sp. nov. in occlusal view. Notes: (a) IVPP V 17810, right maxillary fragment with M1-3; (b) V 17811.1, right M1; (c) V 17811.3, right M2; (d) V 17811.5, left m1; (e) V 17811.9, right m1; (f) V 17811.10, left m2. hypocone. The posteroloph is thin and long, and runs from the Comparisons hypocone to the posterolabial corner of the tooth. The mesol- The new specimens from the Erden Obo possess characters of oph is usually long and reaches the labial border (present in 2 Heosminthus, including: upper molars are small and have three specimens of a total of 3 specimens), but it is of medium length roots; labial cusps are opposite to lingual cusps; anterior arm of in V 17810 (Figure 2(a)). The entoloph is continuous. A small protocone of M1 is separated from paracone by a shallow groove; mesostyle is present. The sinus is broad and shallow. M1 has complete protoloph II; mesoloph is medium in length The M2 is trapezoidal in occlusal outline, longer than wide or long; metaloph of M1-2 joins anterior arm of hypocone; and and narrower posteriorly than anteriorly (Figure 2(c)). The labial mesolophid of m1-2 is long. anteroloph is long, and the lingual anteroloph is short. The dis- Heosminthus includes three previously described species: tinct protoloph I is connected with the anterior arm of the pro- H. primiveris, H. borrae, H. chimidae, and H. sp.. H. primiveris tocone, the protoloph II is slightly weaker and lower than the was named and described by Wang (1985) based on specimens protoloph I, and connected with the entoloph. The metaloph is from the Qujing basin in Yunnan. H. nomogenesis is slightly transverse and extended to the hypocone (2/3) or the anterior larger than H. primiveris. In M2 of H.