(multituberculata; mammalia) genera from the lower cretaceous ...

Journal of Vertebrate Paleontology 29(4):1264–1288, December 2009 # 2009 by the Society of Vertebrate Paleontology

ARTICLE

TWO EOBAATARID (MULTITUBERCULATA; MAMMALIA) GENERA FROM THE LOWER CRETACEOUS SHAHAI AND FUXIN FORMATIONS, NORTHEASTERN CHINA NAO KUSUHASHI,*,1,2 YAOMING HU,1 YUANQING WANG,1 TAKESHI SETOGUCHI,2,{ and HIROSHIGE MATSUOKA2 1 Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, People’s Republic of China, [email protected]; 2 Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

ABSTRACT—Two eobaatarid multituberculate genera including three species from the Lower Cretaceous (AptianAlbian) Shahai and Fuxin formations in Liaoning Province, northeastern China are described here: Sinobaatar xiei sp. nov., S. fuxinensis sp. nov., and Liaobaatar changi gen. et sp. nov. Sinobaatar xiei is characterized by m1 with cusp formula 3:2 (labial:lingual), P4 with cusp formula 2:4, blade-like P5 with three cusps anteroposteriorly arranged, M1 with cusp formula 4:4, and M2 with cusp formula 3:4. P1 to P3 of S. xiei lack distinct posterior cingulum. Sinobaatar fuxinensis has a more distinct posterior cingulum on P1 to P3, and its M2 has cusp formula 3:3. Sinobaatar xiei is within the size range of most other eobaatarids, and S. fuxinensis is slightly larger than S. xiei. Liaobaatar changi is clearly larger than other eobaatarids. The ratio of p4 length and height of L. changi and S. xiei (L./S.) are 1.9 and 1.7, respectively. Liaobaatar changi is also characterized by m1 with cusp formula 3:3. A specimen of S. fuxinensis indicates that tooth replacement in eobaatarids occurred in the typical backward sequence seen in Late Cretaceous-Tertiary multituberculates.

INTRODUCTION The Early Cretaceous is an important and interesting period in the evolution of the Multituberculata, an order of mammals that appeared in the Middle Jurassic and became extinct in the Eocene to Oligocene. They were a major group of the Mesozoic mammalian fauna in the northern continents. Most multituberculates of the Late Cretaceous and the Cenozoic belong to the monophyletic suborder Cimolodonta (Kielan-Jaworowska and Hurum, 2001; Kielan-Jaworowska et al., 2004). Fossil records suggest that the Cimolodonta derived from the paraphyletic group of “plagiaulacidans” in the late Early Cretaceous (Kielan-Jaworowska and Hurum, 2001). Descent of cimolodontans from “plagiaulacidans” represents an evolutionary transition within multituberculates before the group reached a greater diversity in the Late Cretaceous. Early Cretaceous “plagiaulacidans” are the key fossil evidence for this transition. The Eobaataridae is an advanced family of the “plagiaulacidans.” Eobaatarids are considered to be closely related to cimolodontans (Kielan-Jaworowska and Hurum, 2001; KielanJaworowska et al., 2004), and occupied an interesting position in the “plagiaulacidan”-cimolodontan transition. Several genera are now known for this family: Eobaatar Kielan-Jaworowska, Dashzeveg, and Trofimov, 1987, Hakusanobaatar Kusuhashi, 2008, Loxaulax Simpson, 1928, Monobaatar Kielan-Jaworowska, Dashzeveg, and Trofimov, 1987, Sinobaatar Hu and Wang, 2002, and Tedoribaatar Kusuhashi, 2008 (Kielan-Jaworowska and Hurum, 2001; Kielan-Jaworowska et al., 2004; Kusuhashi, 2008). Parendotherium Crusafont-Pairo´ and Adrover, 1966, either belongs to the Eobaataridae, or can be assigned to the Paulchoffatiidae (Kielan-Jaworowska et al., 2004; Hahn and Hahn, 2006).

*

Corresponding author. Current address: Department of Earth’s Evolution and Environment, Graduate School of Science and Engineering, Ehime University, Ehime 790-8577, Japan. { Current address: Fukada Geological Institute, Tokyo 113-0021, Japan.

A putative taxon ?Janumys Eaton and Cifelli, 2001 was also attributed to the Eobaataridae (Hahn and Hahn, 2006). Most of them are based on fragmentary fossil records, and therefore, more and better preserved materials would be valuable. In Asia, several strata have yielded Early Cretaceous multituberculates (e.g., Kielan-Jaworowska et al., 1987; Hu and Wang, 2002; Kusuhashi, 2008). Most multituberculates discovered from the Lower Cretaceous of Asia belong to the Eobaataridae. The Lower Cretaceous Shahai and Fuxin formations of Liaoning Province, China are very productive for mammalian fossils. Multituberculates and eutherians are the two major mammalian fossil groups known from these strata. More than 30 multituberculate specimens have been discovered, and most are attributed to the Eobaataridae. Here we describe three new eobaatarid species of two genera, including one new genus, from the Shahai and Fuxin formations, and briefly discuss the dental replacement pattern of eobaatarid multituberculates based on one specimen of a young individual. Institutional Abbreviations—IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China; PIN, Paleontological Institute of the Russian Academy of Sciences, Moscow, Russia; SBEI, Shiramine Institute of Paleontology, Hakusan City Board of Education, Ishikawa Prefecture, Japan (formerly Shiramine Village Board of Education, Ishikawa Prefecture). GEOLOGIC SETTING Present materials were recovered from the Shahai Formation (Shahai Shale Formation in Muroi, 1940) of the Badaohao District (Heishan County) and the Fuxin Formation (Coal Series of Fuhsinhsien in Wang and Huang, 1929; Fu-hsin Series in Morita, 1939) of the Fuxin District, western Liaoning Province, northeastern China. In western Liaoning Province, the late Mesozoic non-marine sediments have a wide distribution (e.g., Wang et al., 1989; Yang and Li, 1997; Jiang and Sha, 2006; Fig. 1). Several different stratigraphical correlations of these sediments have been proposed by previous authors, and here we follow those of

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FIGURE 2. Stratigraphic table of the major late Mesozoic strata distributed in western Liaoning Province, northeastern China. Mammalian fossil records are based on Meng et al. (2006) and Luo et al. (2007) and references therein. Radiometric ages are based on previous studies cited in the text. FIGURE 1. Distribution of the late Mesozoic strata in Liaoning Province (gray areas of enlarged map; modified after Editorial Board of Chinese Geologic Maps, 2002) and locations of Fuxin and Badaohao, Liaoning Province, northeastern China.

Wang et al. (1989), Yang and Li (1997), and Editorial Board of Chinese Geologic Maps (2002). The authors of stratigraphic nomenclatures are cited from Yang and Li (1997) and Zhang (2001). See Yang and Li (1997) for further information about stratigraphic nomenclatures. Major late Mesozoic strata distributed across western Liaoning Province include the Tuchengzi Formation (Tuchengzi Conglomerate in Lin, 1942 cited in Yang and Li, 1997), the Jehol Group (Jehol Series in Grabau, 1923) composed of the Yixian Formation (Yihsien Formation in Grabau, 1923) and Jiufotang Formation (Jiufotang Series in Endo, 1934), and the Shahai, Fuxin and Sunjiawan (Sunchiawan Series in Morita, 1939) formations, in an ascending stratigraphic order (Fig. 2). The Tuchengzi Formation is correlated to the ?Upper JurassicLower Cretaceous, and the other five formations are Lower Cretaceous (Wang et al., 1989; Jin, 1996; Yang and Li, 1997; Swisher et al., 2001; Editorial Board of Chinese Geologic Maps, 2002). The Shahai and Fuxin formations are attributed to the Jehol Group by some authors (e.g., Hao et al, 1982; Yang and Li, 1997). Jiang and Sha (2006) interpreted the Shahai Formation as the upper part of the Jiufotang Formation. The Haizhou Formation, referred to by some authors (e.g., Chen et al., 1980; Li et al., 1982; Wu et al., 1992; Zhu and Zhang, 1992), is considered to be synonymous with the Fuxin Formation (Yang and Li, 1997). We follow this synonymy in the present paper. In the Fuxin-Yixian-Jinzhou Basin, the Shahai Formation conformably overlies the Jiufotang Formation and is overlain by the Fuxin Formation with conformity (Wang et al., 1989; Jin, 1996; Fig. 2). Some authors have claimed that an unconformity lies between the Shahai and Jiufotang formations (e.g., Chen, 1988). Mammalian fossils were collected from coaly siltstones in the middle part of the formation, which mainly consists of sand-

stones and mudstones with richly intercalated coal measures, with other vertebrate remains of fishes, lizards, turtles and dinosaur teeth, bones, and egg shells (e.g., Jin, 1996; Hu, Fox et al., 2005). Mammals known from the formation include eutriconodontans, “symmetrodontans” such as Heishanlestes changi Hu, Fox, Wang, and Li, 2005, multituberculates including specimens reported in the present paper, the “eupantotherian” Mozomus shikamai Li, Setoguchi, Wang, Hu, and Chang, 2005, and eutherians (Wang et al., 1995; Hu, Fox et al., 2005; Hu, Wang et al., 2005; Kusuhashi, 2005; Li et al., 2005; Kusuhashi, Hirasawa et al., 2007; Kusuhashi, Hu et al., 2007). The Fuxin Formation is mainly exposed in the Fuxin-YixianJinzhou Basin; it conformably overlies the Shahai Formation (Wang et al., 1989; Yang and Li, 1997) and is overlain by the Sunjiawan Formation with conformity (Jin, 1996) or unconformity (Editorial Board of the Fuxin Mining Bureau, 1994; Yang and Li, 1997; Fig. 2). Wang et al. (1989) recognized the upper part of the Fuxin Formation and the lower part of the Sunjiawan Formation as separate units, although this has not been accepted by many other authors (e.g., Chen and Jiang, 1990; Yang and Li, 1997; Komatsu and Chen, 2000). Jiang and Sha (2006) divided the Sunjiawan Formation into two formations and indicated that the lower one disconformably overlies the Fuxin Formation. The Fuxin Formation is mainly composed of mudstones, sandstones and conglomerates, intercalated with many coal measures. Much of the formation has been interpreted as alluvial fan deposits (Morita, 1939; Muroi, 1940; Wang et al., 1989; Wu et al., 1992). Fossil mammals including eutriconodontans, “symmetrodontans,” multituberculates reported in the present paper, and eutherians including Endotherium niinomii Shikama, 1947, have been found from several coaly horizons of the formation (e.g., Shikama, 1947; Wang et al., 1995; Wang, Y.-Q., Hu et al., 2001; Kusuhashi, Hirasawa et al., 2007; Kusuhashi, Hu et al., 2007) with other vertebrate remains of fishes, turtles, lizards such as Teilhardosaurus carbonarius Shikama, 1947, and dinosaur teeth, bones, and footprints (e.g., Shikama, 1947; Young, 1960; Wang et al., 1989). Multituberculates and eutherians are major components of the mammalian assemblage.

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Neither reliable radiometric ages nor index fossils have been reported from the Shahai and Fuxin formations. The Fuxin Formation used to be correlated with the Middle (e.g., Morita, 1939) or Upper Jurassic (e.g., Muroi, 1940; Shikama, 1947; Chen et al., 1980) by fossil plants and mollusks. Now the formation is considered to be Lower Cretaceous by many authors (e.g., Zhang, 1987; Chen, 1988; Wang et al., 1989; Yang and Li, 1997; Chen et al., 2006). Chow (1953) and Patterson (1956) also considered the presence of Endotherium in the Fuxin Formation to indicate an Early Cretaceous age for the unit. Chen (1999) stated that the Fuxin Formation is not younger than the Hauterivian, whereas Mao et al. (1990) suggest that the presence of tricolpate angiosperm pollen indicates that the formation is not older than the Aptian. Although K-Ar dates ranging from 100 to 137 Ma for the Fuxin Formation was suggested by Mao et al. (1990), these results are not reliable because the ranges of errors are not available and the age ranges are too wide. Wang et al. (1995) considered the Shahai and Fuxin formations to be ?Valanginian or ?Hauterivian and not later than Aptian, respectively. Here, the age of the Shahai and Fuxin formations is estimated on the basis of radiometric ages reported from the underlying Jehol Group (the Yixian and Jiufotang formations). The Jehol Group, especially the Yixian Formation, yields well preserved fossils, and its biostratigraphical correlation has been attempted by many authors. The group was initially assigned to the Cretaceous (Grabau, 1923), and later it became correlated with the Jurassic (e.g., Chen et al., 1980; Li et al, 1982; Chen, 1988; Wang et al., 1989; Chen, 1999). In the past 2 decades, radiometric ages of 120 to 130 Ma have been reported for the Yixian and Jiufotang formations (Eberth et al., 1993; Smith et al., 1995; Swisher et al., 1999; Wang, S.-S., Hu, et al., 2001; Wang, Wang, et al., 2001; Swisher et al., 2001; He et al., 2004), and the Jehol Group is now generally thought to be Barremian to Aptian in age (Gradstein et al., 2004). Though some much older ages (around 145 Ma) have also been reported for the Yixian Formation (e.g., Lo et al., 1999), these abnormally old ages are interpreted to be biased by the weathering of biotites and the open of K-Ar system by other investigators (Swisher et al., 2001). Because the Shahai Formation overlies the Jiufotang Formation, and the Fuxin Formation overlies the Shahai Formation, the Fuxin and Shahai formations are interpreted to be the Aptian or younger on the basis of radiometric ages of the underlying Jehol Group. However, there is no evidence to constrain upper depositional age limit of the Shahai and Fuxin formations. Here we tentatively attribute them to the Aptian to Albian, taking account of their stratigraphic relationships with the underlying Jehol Group. SYSTEMATIC PALEONTOLOGY Order MULTITUBERCULATA Cope, 1884 Family EOBAATARIDAE Kielan-Jaworowska, Dashzeveg, and Trofimov, 1987 SINOBAATAR Hu and Wang, 2002 Type Species—Sinobaatar lingyuanensis Hu and Wang, 2002. Included Species—Type species, S. xiei sp. nov., and S. fuxinensis sp. nov. Emended Diagnosis—Dental formula 3?.0.5.2/1.0.3.2; lower incisor gracile, completely covered with enamel; p2 singlerooted, peg-like; p3 double-rooted, crown shape oval rather than triangular or rectangular in lateral view; p4 having eight to 11 serrations and one posterior labial cusp; m1 cusp formula 3-4:2 (labial:lingual); m2 cusp formula 1 (coalesced):2; I2 simple conical but somewhat stout; I3 single-rooted, transversely wide and longitudinally compressed, situated at lateral margin of premaxilla; P1 to P3 having three cusps triangularly arranged (cusp formula 1:2); P3 smaller than P1 and P2; P4 cusp formula 2-3:4; P5 having three main cusps anteroposteriorly arranged; M1 having

posterolingual wing, cusp formula 4:4; M2 cusp formula 3:3-4. Differing from Eobaatar in lower incisor completely covered with enamel, cusp formula and morphology of P4 and P5. Differing from Hakusanobaatar in cusp formula of P4 and P5. Differing from Janumys in having posterolingual wing of M1. Differing from Loxaulax in relatively straight anterior margin of M2 and cusp formula of m1. Differing from Monobaatar in P3 smaller than P1 and P2. Differing from Parendotherium in simple conical shape of I2. Differing from Tedoribaatar in having p2 and double rooted p3. SINOBAATAR XIEI sp. nov. (Figs. 3–7; Tables 1, 2) Holotype—Partial skull including maxillae with right (P1-M2) and left (P1-P5 and M2) dentitions, fragment of left premaxilla with I2 and I3, damaged right basicranial region with squamosal, fragment of left dentary with damaged p4 and m1, and right dentary with incisor, p2-m2 (IVPP V14491; Figs. 3–5). Referred Specimens—Fragmentary left dentary with p3-m2 (IVPP V14477); fragment of right dentary with p2-m2 (V14478); fragmentary right dentary with incisor, p3-m1 (V14480); broken right dentary with incisor, damaged p4, m1 and m2 (V14485); damaged left dentary with broken incisor, p2-m2 (V14487; Fig. 6); fragmentary left dentary with incisor, p2-p4 (V14488); a part of right dentary with p2-m1 (V14495); fragmentary left dentary with p4 and m1 (V14496); a part of right dentary with damaged p4 (V14497); damaged left dentary with incisor, p3-m2 (V14502); a part of left dentary with p4-m2 (V14508); fragmentary right maxilla with two cusps of P3, P4-M2 (V14481); and fragment of right maxilla with P1-P4 (V14486; Fig 7). Locality and Horizon—Fuxin, Liaoning, northeastern China; Early Cretaceous (Aptian to Albian); the Fuxin Formation. Etymology—In honor of Mr. Shuhua Xie who has prepared a lot of fragile and tiny specimens from Fuxin and Badaohao with his great technique. Diagnosis—Lower p4 having eight to nine serrations; P5 having only three cusps arranged anteroposteriorly; P1 to P3 without distinct posterior cingula; P4 cusp formula 2:4; M1 cusp formula 4:4; M2 cusp formula 3:4. Differing from Sinobaatar lingyuanensis in cusp formula of P4 and P5. Differing from S. fuxinensis in lack of distinct posterior cingulum on P1 to P3 and cusp formula of M2. Description—Left and right lower jaw fragments, lower incisors, premolars and molars, upper jaw, upper incisors, premolars and molars are preserved in the specimens of Sinobaatar xiei. Upper I1 has yet to be discovered. Dentaries are relatively well preserved in IVPP V14491, and damaged and/or fragmentary dentaries are preserved in V14477, V14478, V14480, V14485, V14487, V14488, V14495, V14496, V14500, V14502, and V14508. The dentary of V14478 has not been removed from matrix, and only the lingual side is observable. Dentaries of V14491 have not been removed, either. The dentaries can only be observed on the lingual side of the right dentary and the labial side of the broken left dentary. The anterior part of the dentary bends anterodorsally, and the symphysis extends approximately one-third the length of premolar part of the dentary on the lingual side. The horizontal ramus is deepest dorsoventrally below p4. A mental foramen is situated approximately 1 mm anterior to p3 in V14477, about 1 mm anterior to p2 and 2 mm above the ventral margin of the dentary in V14487. The coronoid process extends posterodorsally from slightly posterior to m1. The condyle is placed slightly below the occlusal level of molars and facing posterodorsally. The masseteric fossa extends anteriorly below the posterior root of p4 on the labial surface of the horizontal ramus. The ventral margin of dentary is inflected lingually, forming a pterygoid shelf. The shelf is more prominent below the coronoid process.


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FIGURE 3. Sinobaatar xiei sp. nov., holotype (IVPP V14491). A SEM photograph of a resin cast (A) and a line drawing (B). Scale bar equals 4 mm. Abbreviations: d, dentary; L, left; Mx, maxilla; Pr, pterygoid ridge; Prm, promontorium; R, right; Sq, squamosal.

Lower incisors are preserved in V14480, V14485, V14488, V14491, and V14502, and poorly preserved in V14487. Lower incisor is slender with rounded labial surface and more flattened lingual one. It is thinner toward the tip of the tooth. The ventral

margin of the lingual surface is slightly swollen. It bends slightly dorsally. Enamel completely covers the lower incisor. Lower incisor of V14502 has a relatively flat facet near its base on the dorsolabial surface, which we interpret to represent a wear facet.

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FIGURE 4. Sinobaatar xiei sp. nov., holotype (IVPP V14491). SEM photographs of a resin cast (A1, B1) and line drawings (A2, B2) of the right upper dentition. A. In labial view. B. In occlusal view. Scale bar equals 2 mm.

Lower p2s are preserved in V14478, V14487, V14488, V14491, and V14495. It is a tiny, peg-like and non-functional tooth. It situated immediately anterior to the anterior root of p3 and below the crown of p3. Lower p3s are preserved in V14477, V14478, V14480, V14487, V14488, V14491, V14495, and V14502. The crown shape of p3 is oval rather than triangular or rectangular in lateral view, being much similar to those of Sinobaatar and Hakusanobaatar (Hu and Wang, 2002; Kusuhashi, 2008), and the crown leans posterodorsally. Lower p3 is double-rooted and the anterior root is robust; the posterior one is thinner than the anterior. There are two small

serrations accompanied by short and indistinct ridges extending anteroventrally. The mesioventral part of the crown hangs over a tiny p2. The height of p3 comes to that of the anterior margin of p4. Left and right p4s are preserved in all of lower jaw specimens (V14477, V14478, V14480, V14485, V14487, V14488, V14491, V14495, V14496, V14497, V14502, and V14508), although p4s of V14485, V14497 and V14501 are badly damaged. The crown shape in lateral view is parallel-sided, and is neither fully rectangular nor fully arcuate; anteroposterior length is not much longer than height. U-shaped anterior triangular lobe is large relative to crown size and points ventrally. Eight to nine serrations are


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FIGURE 5. Sinobaatar xiei sp. nov., holotype (IVPP V14491). SEM photographs (A1, B1, C1), line drawings (A2, B2, C2), and an X-ray radiograph (D) of the right premaxilla with I2 and I3. A. In labial view. B. In lingual view. C. In occlusal view. Scale bar equals 2 mm.

present on p4, and except for the first one, these are accompanied by ridges on the lingual and labial sides of the crown. The last ridge is variable among the sample, and can be absent in some specimens. The last ridge on the labial side, if present, tends to be worn. A posterior labial cusp is present at a lower position, near the crown-root junction. Dorsal to the cusp, a wear facet extends to slightly anterior to the cusp, and this facet reaches the last serration or higher. Because of the presence of the anterior lobe and the posterior labial cusp, the labial side of p4 does not mirror the lingual side as seen in Argentodites Kielan-Jaworowska et al., 2007. The first lower molars are preserved in V14477, V14478, V14480, V14485, V14487, V14491, V14495, V14496, V14502, and V14508, although the m1 of V14485 is badly damaged. The tooth is asymmetrical with an oblique posterior margin in occlusal view. Cusp formula is 3:2. In the labial row, the second and third cusps are obviously separated but the first cusp is not well separated from the second. The first cusp is much smaller than the second. The second labial cusp is the tallest in the labial row in most specimens, but it is as tall as the third one in several specimens. At the lingual surface near the tip of the third cusp, a small pit is present in V14478 and V14480, which subdivides the third cusp. The labial cusp row is situated just posterior to, and is almost the same height as, the posterior labial cusp of p4; it is heavily worn in some specimens. Lingual cusps are crescentic and face towards the middle of the tooth. They are in subequal size and much taller than the labial cusps. Each labial wall of the lingual cusps is ornamented by a faint groove. Lingual surfaces of the second and third labial cusps are occasionally ornamented by indistinct grooves. The second lower molars are preserved in V14477, V14478, V14485, V14487, V14491, V14502, and V14508. The tooth is asymmetrical with a strongly oblique posterior margin in the occlusal view. Cusp formula is 1 (coalesced):2. The labial cusp is long anteroposteriorly and is shaped like a protruded labium. Previous studies described this type of labial cusp as three coalesced cusps (e.g.,

Kielan-Jaworowska et al., 1987; Hu and Wang, 2002). It is probably based on the number of grooves dividing this cusp into three parts, which also observed in the present materials. The number of grooves is, however, not obvious because of hard wear in some specimens. Thus, we prefer to describe this cusp as one long cusp. The posterior part of the cusp is taller than the anterior. The lingual wall is ornamented by grooves and pits. This ornamentation is variable among the specimens. A deep groove in the labial cusp in V14478 reaches the dorsal margin of the cusp. Lingual cusps are subequal in height and the anterior one is slightly larger than the posterior one. They are crescentic and face labially. Each labial surface of the lingual cusps is ornamented by a groove. The maxillae are well preserved in V14491 (although the left side is less well preserved), and partly preserved in V14481 and V14486 with some damage. Left and right maxillae have not been removed from matrix in V14491. They are partially covered by the left dentary but nonetheless partially observable. Pterygoids and alisphenoids are preserved at the posterior part of the specimen. They are, however, badly damaged and only the ridge of the right pterygoid can be identified. On the left zygomatic arch, the anterior zygomatic ridge is present, whereas this part of the right maxilla is damaged. Anterior to the left zygomatic arch, there is a damaged infraorbital foramen situated above the interstice between P3 and P4. The right basicranial region and a part of the right squamosal with the glenoid fossa and posterior portion of the zygoma are preserved as isolated elements in V14491. They are not removed from the matrix and are visible in ventral view. The basicranial region is crushed and only the anteromedially oriented and damaged ?promontorium can be identified. A cavity is present at the posteromedial part of the ?promontorium, which possibly is a trace of the fenestra cochleae. The fenestra vestibuli is not visible. The flat and broad glenoid fossa has an oval outline in ventral view. Its lateral margin is inflected ventrally. The posterior portion of the

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FIGURE 6. Sinobaatar xiei sp. nov., IVPP V14487. SEM photographs (A1, B1, C1) and line drawings (A2, B2, C2). A. In labial view. B. In lingual view. C. In occlusal view. Line drawings (A2, B2, C2) are enlargements of the cheek teeth region. Scale bars equal 2 mm.

zygomatic arch is relatively thin and slightly damaged. The suture between the maxilla and squamosal can not be identified. Left I2 is preserved in V14491. I2 is a single-rooted simple but somewhat stout tooth without any cuspules. The crown points anteroventrally, and is slightly bent posteriorly. Its posterolingual surface is relatively flat, possibly caused by wear. A long root curves posteriorly and extends posteriorly nearly to the end of the root of I3 (Fig. 5). A single-rooted left I3 preserved in V14491 is situated at the lateral margin of premaxilla, not medially situated as seen in cimolodontans from the Asian Upper Cretaceous. It is a bladelike tooth compressed longitudinally and has two serrations. The anterior surface of the tooth is almost flat, whereas the posterior surface is slightly bellying. The anterior surface is ornamented by longitudinal fine ridges, whereas the posterior surface is smooth. The morphology of I3 is similar to that of Sinobaatar lingyuanensis. Hakusanobaatar also has an anteroposteriorly thin I3 (Kusuhashi, 2008), but the leaf-shaped, non-serrated crown of the latter taxon is different from that of S. xiei.

The anterior three premolars are preserved in V14486 and V14491, and only two cusps of lingual row of the right P3 are preserved in V14481. The left P1 of V14491 is collapsed under the left p4 overlying it. P1 to P3 have similar shape with three subequal and triangularly arranged cusps; one on the labial side and two on the lingual, all ornamented with radiating ridges. Cuspules are not present on P1 to P3. P1 is slightly larger than P2, and P3 is smaller than the other two. The posterolingual part of P2 and P3 slightly project posteriorly, forming posterior cingula, but they do not quite protrude. The posterior cingulum is more developed in P3 than in P2. The anterior part of P3 and P4 hang over the posterior cingulum of P2 and P3, respectively; the posterior part of P1 is slightly overlapped by P2. P4s are preserved in V14481, V14486, and V14491. Cusp formula is 2:4. The second labial cusp is larger and taller than the first one. The cusps of the lingual row increase in size and height posteriorly, the fourth cusp being the largest and tallest. In V14486 and V14491, there is a tiny cuspule situated transversely midway along the anterior margin of the tooth. Another tiny


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FIGURE 7. Sinobaatar xiei sp. nov., IVPP V14486. SEM photographs (A1, B1, C1) and line drawings (A2, B2, C2) of the dentition. A. In labial view. B. In lingual view. C. In occlusal view. Scale bar equals 2 mm.

cuspule is present at the posterior end of the lingual cusp row in V14486. The right P4 of V14481 has no cuspule. The lingual wall of the tooth forms a shearing surface. All cusps are ornamented with faint, fine and short ridges. The crown is asymmetrical with an oblique posterior margin in occlusal view. The second cusp of the labial row is positioned about opposite the third cusp of the lingual row, and forms the posterolabial margin of the tooth. P5s are preserved in V14481 and V14491, though the left P5 in V14491 is not well exposed because of overlying left dentary. The crown is rather blade-like and has a rectangular outline in occlusal view. There is only one cusp row with three main cusps arranged slightly obliquely and in distolabial orientation to the longitudinal axis of the crown. Cusps are not conical, connected by ridges, and increase in size and height posteriorly. The third cusp, situated at the longitudinal mid-point of the tooth, is the largest and highest. From the tip of the third cusp, a ridge extends toward the distolabial corner of the tooth. There is a ridge extending toward the third cusp from the posterolingual corner, although it does not reach the third cusp. The posterolingual ridge bears three worn nodes in V14481. The posterior basin is only incipient, not well developed. All cusps are ornamented with fine striae. M1s are preserved in V14481 and V14491. The anterolabial part of M1 in V14481 can not be observed because the displaced P5 hangs over the tooth. Only a posterior cusp of the lingual

cusp row and posterior part of the lingual ridge of the left M1 are observable in V14491. The cusp formula is 4:4. All cusps, except for the first labial cusp, are well separated and have approximately the same height. In the labial cusp row, the first cusp is smaller than the others and not well separated from the second one. The second labial cusp is the largest in the labial cusp row. There is a hollow posterior to the last labial cusp. The lingual cusps are transversely wider than the labial ones; the valley between the two cusp rows is oblique and somewhat labially situated, and in distolabial orientation to the longitudinal axis of the crown. The fourth lingual cusp is thinner than the others and the third one is anteroposteriorly the widest in the row. In the lingual cusp row, the first and last cusps are about the same size and smaller than the other two; sizes of the second and third cusps are similar. The labial cusps are positioned about opposite the embrasures between the cusps of the lingual row. The posterolingual wing with a ridge is present in V14491; the anterior end of the wing reaches the anterior end of the third lingual cusp. The lingual surface of M1 is flattened by wear in V14481, and its posterolingual wing is absent. The posterior margin is slightly oblique to the longitudinal axis of the tooth. The posterior ends of the cusp rows are connected by a ridge. M2s are preserved in V14481 and V14491. M2 is roughly trapezoidal in occlusal view, with a straight anterior margin. Cusp formula is 3:4. All cusps except for the first lingual cusp are

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nearly subequal in height. The first labial cusp is longer than the other two. The first and second cusps in the labial row are less separated than the second and third cusps. The first lingual cusp is the shortest and smallest in the lingual cusp row. The second and third cusps in the lingual row are almost same size, and the last one is smaller than these two cusps. An anterolabial wing is present but without obvious ornamentation. M2 of V14481 has a weak ridge extending anterolabially from the tip of the last labial cusp. This ridge forms the edge of the anterolabial wing, and passes through the anterior base of the first labial cusp as the anterior margin of the tooth. The valley between the labial and lingual cusp rows is situated just posterior to the valley between the lingual cusp row and the ridge of the wing of M1. Measurements—See Tables 1 and 2. Discussion—Sinobaatar xiei resembles S. lingyuanensis in many dental features, such as the oval p3 in lateral view, the longitudinally compressed I3 with two serrations, and especially the outlines of P5, which is previously only seen in S. lingyuanensis. Sinobaatar xiei also shares cusp formulae of M1 and M2 with S. lingyuanensis. The cusp formula for M1 of S. lingyuanensis was considered to be 3:4 in the original description (Hu and Wang, 2002). However, on the basis of our observation, there probably was a cusp anterior to the anteriormost preserved cusp in the labial cusp row, and, correctly, the cusp formula is 4:4. TABLE 1. Measurements of lower teeth in Sinobaatar xiei sp. nov., S. fuxinensis sp. nov., Liaobaatar changi gen. et sp. nov., Hakusanobaatar matsuoi, Tedoribaatar reini, S. lingyuanensis, and Eobaatar magnus. p3 Sinobaatar xiei IVPP V14491 left right V14477 V14478 V14480 V14485 V14487 V14488 V14495 V14496 V14497 V14502 V14508 Sinobaatar fuxinensis V14160 left right V14479 V14490 V14499 Liaobaatar changi V14489 left right V14483 V14500 Hakusanobaatar matsuoi SBEI 1736 Tedoribaatar reini SBEI 1570 Sinobaatar lingyuanensis IVPP V12517 Eobaatar magnus PIN 3101-57

p4

m1

m2

L

H

L

H

L

W

L

W

1.2 1.3 1.1 1.5

1.7 2.0 1.7 1.7

— 3.1 3.3 3.2 3.1

2.4 2.3 2.4 2.6 2.3

1.7 1.8 1.6 1.7

— 1.5 1.5 1.2

1.8 1.9 1.8

— 1.9 1.9

1.0 — 1.6

1.7 2.1 —

1.4

1.8 1.7

1.8 1.7

1.7 1.7

1.4 1.4

1.9

2.2 2.4 2.5 2.5 — 2.4 2.5

1.7

1.4

2.8 3.5 3.5 3.5 3.5 3.3 3.5

1.6 1.9

1.4 1.4

1.3 1.4 1.4 1.2

2.4 2.4 1.7 1.8

2.3 2.2 1.8 2.2 1.0

1.2

1.7 1.8

1.8 1.7

2.1

—

4.0

2.6

1.7

1.4

1.9

1.7

4.2

3.0

1.8

1.7

2.1

1.8

2.8 2.7 2.2 2.5

6.8 6.4 6.0

4.6 3.6 4.0

2.6 2.5 2.2 2.6

2.0 2.0 1.9 2.0

2.7

1.9

1.4

3.5

2.1

3.7

2.4

4.1

2.5

3.5

2.0

1.9

Personal data of N. K. for E. magnus and S. lingyuanensis, and data of H. matsuoi and T. reini are after Kusuhashi, 2008. Abbreviations: H, height; L, longitudinal length; W, transverse width.

These similarities indicate close affinity of Sinobaatar xiei with S. lingyuanensis. Sinobaatar xiei is distinguished from S. lingyuanensis by having no cuspules on the labial surface of P5 (Hu and Wang, 2002; Kielan-Jaworowska et al., 2004). It is also different from S. lingyuanensis in having two labial cusps on P4 rather than three (Hu and Wang, 2002; Kielan-Jaworowska et al., 2004). The serrations of p4 in S. xiei (eight to nine) are fewer in number than in S. lingyuanensis (11; Hu and Wang, 2002). These differences validate that S. xiei is not conspecific with S. lingyuanensis, and S. xiei is erected as a new species of Sinobaatar. Species of Sinobaatar have gracile lower incisors which are not greatly thickened toward their bases, and the bases of the incisors are narrow. This gracile lower incisor is common among eobaatarids. Hakusanobaatar also has such lower incisors (Kusuhashi, 2008), and those in Liaobaatar are not thickened toward the base, as mentioned below. Eobaatar has a limited enamel band on the anterior surface of the lower incisor (Kielan-Jaworowska et al., 1987), and which distinguishes it from other eobaatarids. But lower incisors of Eobaatar probably have a narrow base such as that seen in Sinobaatar and Hakusanobaatar. Non-eobaatarid “plagiaulacidans” whose lower incisors are known generally have stouter lower incisors with more thickened bases than eobaatarids (e.g., Hahn, 1978; Hahn and Hahn, 1999, 2004; Kielan-Jaworowska and Hurum, 2001), though Iberodon Hahn and Hahn, 1999, has relatively slender one (Hahn and Hahn, 1999). Robust lower incisors are also seen in most cimolodontans, except for the Ptilodontoidea (Kielan-Jaworowska and Hurum, 2001; Kielan-Jaworowska et al., 2004). Cimexomys Sloan and Van Valen, 1965, is another exception (Montellano et al., 2000), and its lower incisor is morphologically similar to those of Sinobaatar and some other eobaatarids. It has a ventral ridge on the lingual surface (Montellano et al., 2000). A similar structure is also seen in the lower incisors of several eobaatarids such as Sinobaatar, Liaobaatar, and Hakusanobaatar, as the swollen ventral margin of the lingual surface, though the dorsal ridge on the lingual surface of the incisor in Cimexomys is not as obvious as in those eobaatarids. SINOBAATAR FUXINENSIS sp. nov. (Figs. 8–17; Tables 1, 2) Holotype—Flattened skull and dentaries with dentitions (V14160; Figs. 8–10). Right I2, I3, P1-M1, lower incisor, and p2-p4, and left I2, I3, P1-P2, M1-M2, lower incisor, p3, p4 and m2 are observable. Left P3, P5, m1, and right M2 are partly exposed. Referred Specimens—Specimens collected from the Fuxin Formation include: upper jaws with right (I2, DP1, erupting P1, P2M2) and left (I2-I3, erupting P1, P2-M2) dentitions, and fragmentary left dentary with incisor, p2 and p3 (V14490; Figs. 11–15); fragments of right maxilla with P2-P3 and P5, isolated right M1 and right M2, fragment of left dentary with broken incisor, p2, p3 and anterior part of p4 (V14505); fragment of left dentary with incisor, p2-m2 (V14479); fragment of right dentary with p3-m2 (V14499; Fig. 16); fragment of left dentary with posterior half of p4 (V14501); fragment of right (with P1-M2) and left (with P1-P4) maxillae (V14482; Fig. 17); left maxillary fragment with M1 (V14503); and badly damaged right M2 (V14494). A fragmentary right maxilla with P1-P3 (V14507) was collected from the Shahai Formation. Type Locality and Horizon—Fuxin, Liaoning, northeastern China; Early Cretaceous (Aptian to Albian); the Fuxin Formation. Other Locality and Horizon—Badaohao, Heishan, Liaoning, northeastern China; Early Cretaceous (Aptian to Albian); the Shahai Formation. Etymology—After Fuxin City, around where the small coal mines yielding most of present materials are located. Diagnosis—Posterior cingulum of P1 to P3 developed; crowns of P1 to P3 low relative to their lengths; P4 cusp formula 2:4;


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TABLE 2. Measurements of upper teeth in Sinobaatar xiei sp. nov., S. fuxinensis sp. nov.,? Eobaataridae gen. et sp. indet., Hakusanobaatar matsuoi, S. lingyuanensis, and Eobaatar magnus. P1 L

W

Sinobaatar xiei IVPP V14491 left right 1.4 1.1 V14481 V14486 1.5 1.1 Sinobaatar fuxinensis V14160 right 2.1 — V14482 left 1.8 1.3 right 1.8 1.2 V14490 left right V14494 V14503 V14505 V14507 1.8 1.3 ?Eobaataridae gen. et sp. indet. V14506 1.9 1.4 Hakusanobaatar matsuoi SBEI 1736 left 1.4 1.0 right Sinobaatar lingyuanensis IVPP V12517

P2

P3

P4

P5

M1

M2

H

L

W

H

L

W

H

L

W

H

L

W

H

L

W

H

L

W*

H

0.9

1.2 1.3

1.1 1.0

0.9 0.9

1.0 1.0

1.0 0.9

0.8 0.8

1.3 1.2

1.7 1.8

1.5 1.1

0.7 0.6

1.9 1.9 1.6

1.7 1.8 1.5

1.0 0.9 0.8

1.1

1.0

1.2

1.0

0.8

1.0 0.9 0.8 0.7

1.1 1.1

1.3

1.0 1.0 1.0 0.9

2.0 2.0

1.1

1.3 1.3 1.5 1.5

1.2

1.7

—

1.1

1.4

—

0.9

1.8

—

0.9

2.5

—

1.6

1.2 1.2

1.7 1.6

1.2 1.2

0.9 1.0

1.7 1.5

1.2 1.1

0.8 0.9

1.8 1.8

1.2 1.1

1.0 1.0

2.2

1.2

1.4

2.2

1.5

0.8

2.1

1.8

1.0

1.1 1.2

0.9 1.0

0.8 0.8

1.0 1.1

0.9 0.9

0.7 0.7

1.4 1.3

0.9 0.9

0.8 —

2.0 1.9

1.0 1.1

1.2 1.2

1.8 1.7

— 1.2

— 0.6

1.7 1.7 1.9

— 1.6 1.6

— 1.0 0.9

1.3 1.5

1.1 1.2

1.0 1.0

1.2 1.4

1.1 1.1

0.9 0.8

2.0

1.1

1.2

2.2 1.8

1.4 1.4

1.0 0.8

1.9

1.8

1.0

1.4

0.8

0.9

0.9

1.2 1.7

1.6

1.0

1.7

1.1

1.7 1.5

1.2 1.1

1.7

0.8

2.1

1.1

1.8

1.4

1.8

1.1

Eobaatar magnus PIN 3101-66 Personal data of N. K. for E. magnus and S. lingyuanensis, and data of H. matsuoi are after Kusuhashi, 2008. *Measured at anterior widest part. Abbreviations: H, height; L, longitudinal length; W, transverse width.

P5 blade-like having only three cusps arranged anteroposteriorly; M1 cusp formula 4:4; M2 cusp formula 3:3. Differing from Sinobaatar lingyuanensis in cusp formula of P4, P5, and M2. Differing from S. xiei in its larger size, relatively low crowned P1 to P3 with developed posterior cingula, and cusp formula of M2. Description—Left and right lower jaws, lower incisors, premolars and molars, upper jaw elements including two collapsed skulls, upper incisors, a deciduous premolar, premolars and molars are preserved in the specimens of Sinobaatar fuxinensis. Upper I1 has yet to be discovered. The right dentary is well preserved in V14499. V14479 has an incomplete but relatively well preserved left dentary. V14160 includes damaged right and left dentaries. Anterior parts of left dentaries are preserved in V14490 and V14505, but the dentary fragment of V14505 is badly damaged. A chip of the left dentary is preserved in V14501. Dentaries of Sinobaatar fuxinensis are morphologically similar to those of S. xiei. Size difference is almost the only characteristic to distinguish dentaries of S. fuxinensis from those of S. xiei. The dentaries are 22.2 mm in length (right) and 22.0 mm (left), respectively in V14160 and V14499 of S. fuxinensis. By comparison, the dentaries are estimated to be less than 18 mm in V14477 and V14491 of S. xiei. The left lower jaw of S. lingyuanensis is 17.8 mm in length. The lower jaws of V14490 and 14501 are, however, as small as those of S. xiei. The mental foramen in V14160 is situated approximately 0.5 mm anterior to p2 and 3 mm above the ventral margin of dentary in the right lower jaw, and about 1 mm anterior to p3 and 2 mm above the ventral margin of the dentary in the left lower jaw. It is positioned 1 mm anterior to p2 and 3 mm above the ventral margin of dentary in V14479, and is 1 mm anterior

to p2 and 2 mm above the ventral margin of the dentary in V14490. The lower teeth of Sinobaatar fuxinensis are morphologically quite similar to those of S. xiei. Lower incisors, p2s, p3s, p4s, m1s, and m2s are preserved in: V14160, V14479, V14490, V14505; V14160, V14479, V14490, and V14505; V14160, V14479, V14490, V14499, and V14505; V14160, V14479, V14499, V14501, and V14505; V14479 and V14499; V14160, V14479, and V14499, respectively. The incisor of V14505 is broken. Lower incisors of V14160 and V14479 have relatively flat facets near their bases on the dorsolabial surfaces, which probably are wear facets made by occlusion with the upper I2. Only the posterior and anterior parts of p4s are preserved in V14501 and V14505, respectively. In V14160, p4s are not entirely observed. All the lower molars are probably preserved in V14160, but only the left m2 is exposed. Lower teeth, especially p4s of S. fuxinensis are larger than those of S. xiei (Table 1). V14479, V14499, and V14501 are referred to this species based on the sizes of p4. Lower teeth of V14490 and 14501 are, however, smaller than the other specimens of S. fuxinensis and almost same size as S. xiei. They are attributed to this species by upper dental morphology. The number of serrations on p4 is nine. The cusp formula of m1 is 4:2, and is different from that of S. xiei. The third and fourth labial cusps are, however, not well separated, and a few specimens of S. xiei (V14478 and V14480) have a pit subdividing the third cusp. Skull elements are preserved in V14160, V14482, V14490, V14503, V14505, and V14507. Most of them are partial maxillae, except for V14160 and V14490. The maxillae in V14503 and V14505 are in very small pieces, and that in V14507 is badly damaged. Only the buccal sides of the right and left maxillae

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FIGURE 8. Sinobaatar fuxinensis sp. nov., holotype (IVPP V14160). A SEM photograph (A) and a line drawing (B). Scale bar equals 4 mm. Abbreviations: d, dentary; L, left; Mx, maxilla; MxZ, zygomatic arch part of maxilla; Pmx, premaxilla; R, right; Sq, squamosal.

are visible in V14482. Left and right damaged infraorbital foramina are situated approximately 2 mm above p4s in V14482. The collapsed skull roof is preserved in V14160. The palatal part is overlain by dentaries, and is not observable. There probably are left and right premaxillae, maxillae, nasals, lacrimals, frontals, parietals, and squamosals, but they are badly crushed and sutures between them are hardly identifiable. Only the stout left zygomatic arch is relatively well preserved, but zygomatic ridges are not clearly preserved. Infraorbital foramina can not be identified, either. In V14490, dorsoventrally flattened skull is preserved but with a crushed skull roof. Other skull bones are difficult to recognize. Only sutures between nasals and frontals are visible to show a posterior extension of the nasals. Part of the palate in V14490 is observable, but also badly damaged. There are many cracks, and sutures between premaxillae, maxillae and palatines are hardly identifiable. Palatine fissures and palatal vacuities appear to be absent. The zygomatic arch of the maxilla is preserved but damaged. The anterior zygomatic ridge is present on the left side, but not seen on the right due to a damage. Anterior to the left

zygomatic arch, there is a damaged infraorbital foramen situated above the anterior root of P4. I2s and I3s, as preserved in V14160 and V14490, are morphologically similar to those of Sinobaatar xiei. I3 is procumbent probably as a result of dorsoventral compression in V14490, and only the posterior surface can be observed. I2s and I3s of V14160 are obviously larger than those of S. xiei, whereas I2s and I3s of V14490 are as small as those of S. xiei. The posterolingual surfaces of the I2s are relatively flat as seen in S. xiei, supposedly also due to wear. Deciduous upper premolars are preserved in V14490. The right DP1 is partially shed but still attached to the maxilla, close to the erupting permanent P1. The tooth has two roots, and only the posterior one is exposed. The posterior root is transversely wide, and has an anteriorly crooked, irregular shape. The X-ray radiograph shows that the second upper premolar preserved on the right side has crooked and bowed roots (Fig. 15). It is very likely this tooth represents DP2 (Martin, 1997; Luo et al., 2004; Luo and Ji, 2005), though no successor has yet to be formed. The third premolar probably also has irregular roots, though it is less


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FIGURE 9. Sinobaatar fuxinensis sp. nov., holotype (IVPP V14160). A SEM photograph (A) and a line drawing (B) of another side. Scale bar equals 4 mm. Abbreviations: d, dentary; Fr, frontal, L, left; Lc, lacrimal; Mx, maxilla; MxZ, zygomatic arch part of maxilla; NF, nasal foramen; Ns, nasal; Pa, parietal; Pmx, premaxilla; R, right; Sq, squamosal.

obvious than the DP2 in X-ray radiograph (Fig. 15). It is interpreted here as deciduous. The crown shapes of DP1 to DP3 are similar to those of permanent P1 to P3, with triangularly arranged cusps, one in labial and two in lingual. In DP1, the lingual cusps are slightly larger than the labial one, and the posterolingual cusp is the tallest. In DP2 and DP3, the three cusps are subequal in size on each tooth, whereas the labial one is slightly larger than the others in DP3. The crown of DP1 is longer than wide; it is not obvious whether or not this is the original shape of DP1. Crown shapes of DP2 and DP3 are not compressed labiolingually, and not clearly distinguishable from the permanent P2 and P3. They have no cuspule. All cusps are ornamented with radiating ridges. A posterior cingulum is absent on DP1, whereas DP2 and DP3 have a cingulum distal to the second lingual cusp on each tooth. DP1 is slightly smaller than DP2, and DP3 is the smallest. Posterior parts of DP2 and DP3 overlap anterior part of DP3 and P4, respectively. The anterior three upper permanent premolars preserved in V14160, V14482, V14490, V14505, and V14507 have similar

shape with three cusps arranged triangularly, one in labial and two in lingual. In V14490, both right and left permanent P1s are erupting. Profiles of P1 to P3 are similar to those of Sinobaatar xiei with cusps ornamented by radiating ridges and no cuspules, but their crown heights relative to lengths are lower than those of S. xiei (Table 2). The three cusps are subequal in size. Distal to the second cusp of the lingual cusp row on each tooth, there is a posterior cingulum. This cingulum lacks ridges and its morphology is similar to that on the anterior premolars of “Bolodon” elongatus. P3 has the most developed cingulum and that of P1 is least developed. The posterior cingulum of P1 and P2 are much more developed than those of S. xiei. The size of the teeth obviously decreases significantly posteriorly, and P3 is the smallest. The anterior part of P2 overlaps the posterior cingulum of P1, and the posterior cingulum of P3 is overlapped by the anterior part of P4 in V14160, V14482 and V14507. In most cases, the anterior part of P3 overlaps the posterior cingulum of P2. But in the right upper jaw of V14482, the anterior part of P3 is overlapped by the posterior part of P2, probably due to postmortem distortion.

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FIGURE 10. Sinobaatar fuxinensis sp. nov., holotype (IVPP V14160). A SEM photograph (A) and a line drawing (B) of upper and lower dentitions. Scale bar equals 2 mm. Abbreviation: MF, mental foramen.

Both P4s are preserved in V14160, V14482 and V14490, although parts of these teeth are not fully visible in V14160 and V14490. Cusp formula is 2:4, and its profile is similar to that of Sinobaatar xiei. A tiny cuspule is situated midway across the anterior margin of the tooth in V14160 and V14482, but not on visible part of P4s of V14490. The tooth has a nearly rectangular shape in occlusal view, the width of the posterior margin being slightly shorter than that of the anterior in V14482. The posterior margin is oblique to the longitudinal axis of P4 in V14490. The second cusp of the labial row forms the posterolabial margin of the tooth. The first labial cusp is positioned about opposite the embrasures between the first and second cusps of the lingual row, and the second labial cusp is positioned about opposite the third cusp. Both P5s are preserved in V14160 and V14490, and right P5s are preserved in V14482 and V14505. They have the same bladelike crown as those of Sinobaatar xiei. The lingual sides of the right P5s of V14160 and V14482 are not fully visible. Only one cusp row with three cusps is present as in S. xiei and they are arranged slightly obliquely to the longitudinal axis. A tiny cuspule is present at the anterior end of the cusp row in V14482, which has almost same height as the posterior end of the lingual cusp row of P4. The cusps and cuspule are not conical, but are connected by ridges. The cusps increase in size and height toward the third (and posterior-most) cusp, which is the largest and highest and positioned about half-way along the length of the tooth crown. A ridge without a cusp extends to near the posterolabial corner of the tooth from the third cusp. There is an indistinct ridge extending from near the posterolingual corner toward the third

cusp but does not reach it. All cusps are ornamented with striae. The posterior basin is not obviously developed. M1s are preserved in V14160, V14482, V14490, V14503, and V14505. The cusp formula is 4:4. All cusps have approximately the same height in V14482 and V14503, and at least all the lingual cusps have almost the same height and are slightly taller than those of the labial row. Cusps in the labial cusp row slightly decrease in height posteriorly in V14490 and V14505. In the labial cusp row, the first cusp is slightly smaller than the others and not well separated from the second one. The last labial cusp is smaller than the second and third. The last labial cusp has a concave posterior surface. The lingual cusps are transversely wider than the labial ones and increase in width posteriorly. The valley between the two cusp rows is somewhat labially situated. It is oriented slightly distolabially and oblique to the longitudinal axis. In the lingual cusp row, the first cusp is smaller than the others. The first and second cusps are less separated than the other cusps. A U-shaped ridge connects the first labial cusp with the anterior end of the first lingual cusp. The labial cusps are positioned about opposite the embrasures between the cusps of the lingual row. A posterolingual wing with a ridge is present; the anterior end of the wing reaches the lingual wall of the third lingual cusp. The wing is strongly worn in V14505. The anterior margin of the tooth is slightly oblique to the longitudinal axis. M2s are preserved in V14482, V14490, V14494 and V14505; the right M2 in V14494 is badly damaged and the left M2 in V14490 is obscured by a deformed skull element. M2 is roughly trapezoidal in occlusal view, with a sigmoid anterior margin in


FIGURE 11. Sinobaatar fuxinensis sp. nov., IVPP V14490. A SEM photograph (A) and a line drawing (B) of upper jaws with dentitions in dorsal view. Scale bar equals 4 mm. Abbreviations: Fr, frontal, L, left; Lc, lacrimal; Mx, maxilla; NF, nasal foramen; Ns, nasal; Pmx, premaxilla; R, right.

V14482, and with a more straight anterior margin in the other specimens. Cusp formula is 3:3. All cusps are subequal in height. In both the labial and lingual cusp rows, the first and second cusps are less separated than the second and third cusps. The last cusps are slightly smaller than the other two. Upper parts of the labial cusps are slightly bent anteriorly in V14482. The first lingual cusp is longer than the other two. There is a cuspule in front of the first lingual cusp in V14482. The anterolabial wing is ornamented with grooves. In V14482 the anterior part of the wing is rimmed, and the rim extends to the anterolingual base of the first labial cusp, forming the anterolabial margin of the tooth. There is a tiny cuspule at the posterior end of the lingual row in the right M2 of V14490. Measurements—See Tables 1 and 2.

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FIGURE 12. Sinobaatar fuxinensis sp. nov., IVPP V14490. A SEM photograph (A) and a line drawing (B) of upper jaws with dentitions in ventral view. Scale bar equals 4 mm. Abbreviations: L, left; Mx, maxilla; Pmx, premaxilla; R, right.

Discussion—Sinobaatar fuxinensis is similar to S. xiei and S. lingyuanensis in many dental features. This indicates a close affinity of S. fuxinensis with S. xiei and S. lingyuanensis. Sinobaatar fuxinensis is distinguished from S. lingyuanensis by having two labial cusps rather than three on P4, and the absence of cuspules on the labial surface of P5 (Hu and Wang, 2002; Kielan-Jaworowska et al., 2004). Cusp formula of M2 of S. fuxinensis is 3:3, while that of S. lingyuanensis is actually 3:4 (emended from 2:4 by Kielan-Jaworowska et al., 2004). Sinobaatar fuxinensis differs from S. xiei in cusp formula of M2. More developed posterior cingula on anterior premolars, especially on P2, also distinguish S. fuxinensis from S. xiei. Crown heights of P1 to P3 of S. fuxinensis relative to their length are shorter than those of S. xiei. Sinobaatar fuxinensis is larger than S. xiei (Tables 1 and 2). V14479, V14499, and V14501 are ascribed to S. fuxinensis mainly based on their large sizes. There is a clear

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FIGURE 13. Sinobaatar fuxinensis sp. nov., IVPP V14490. SEM photographs (A1, B1, C1) and line drawings (A2, B2, C2) of the fragment of dentary with incisor, p2 and p3. A. In labial view. B. In lingual view. C. In occlusal view. Scale bar equals 2 mm.

size gap between dentaries of S. fuxinensis and S. xiei in addition to the morphological differences mentioned above. Upper cheek teeth including molars of S. fuxinensis are 1.2 to 1.4 times larger than those of S. xiei. Lower p4s of S. fuxinensis are also roughly 1.2 times larger than those of S. xiei. These differences validate S. fuxinensis to be a different species. It is difficult to assess whether some differences are intraspecific or interspecific, given the variation in the available specimens. Two specimens of S. fuxinensis, V14490 and V14505, are smaller than the other specimens of this species, and are almost the same size as S. xiei. They are ascribed to S. fuxinensis based on the cusp formulae of upper cheek teeth. Crown heights of P1 to P3 of V14490 relative to their length are higher than the other S. fuxinensis specimens. Their posterior cingula are moderate. These features are rather similar to those of S. xiei, whereas low crowns of P2 and P3 in V14505 are similar to those of S. fuxinensis. P1s of V14490 were in process of eruption, and thus V14490 is considered to be a younger individual than other specimens of Sinobaatar fuxinensis. Molars of V14490, however, are fully erupted, and they are smaller than those of other specimens of S. fuxinensis (Table 2). Erupting P1s of V14490 are also estimated to be smaller than P1s of other specimens of S. fuxinensis. V14505 also has erupted molars, and its upper cheek teeth are in the size range of S. xiei. These facts imply that the size difference is not because of the age difference. Meng et al. (2006) speculated that sexual size dimorphism would not be distinctive among Mesozoic mammals. It is, however, still difficult to reject the possibility of intraspecific diversity. We tentatively assign both V14490 and V14505 to S. fuxinensis. The fourth and fifth premolars in V14490 are tentatively interpreted here as permanent teeth, because they are morphologically quite similar to those of other specimens. The second premolar has two crooked, “bow-legged” roots in the X-ray.

The third premolar probably has roots of similar shape. These are typical of the deciduous premolars of Mesozoic mammals (Martin, 1997; Luo et al., 2004; Luo and Ji, 2005). It is likely that these are also deciduous teeth although its successor has not yet formed. The condition seen in V14490 provides a constraint on reconstruction of tooth replacement in eobaatarid multituberculates. Diphyodonty of incisors and at least some premolars of multituberculates was discussed by several studies (e.g., Szalay, 1965; Kielan-Jaworowska, 1970; Greenwald, 1988). Two types of tooth replacement pattern have been reported for multituberculates. Greenwald (1988) proposed backward sequential replacement for Late Cretaceous-Tertiary multituberculates. This replacement pattern was assessed by Luo et al. (2004) as characteristic of multituberculates as a whole. Hahn and Hahn (1998), on the other hand, reported forward alternating replacement for the Late Jurassic paulchoffatiid Kielanodon Hahn, 1987. The former pattern, the anterior-posterior sequential replacement, is apparently the most convincing for eobaatarid multituberculates. The fact that the second and third premolars of V14490 have conspicuous curved and irregular roots suggests that these premolars are likely the DP2 and DP3. This shows that S. fuxinensis has a typical backward replacement sequence. It is possible that the intervals between each replacement were relatively long, so that no successors had yet been developed for P2. LIAOBAATAR gen. nov. Type and Only Species—Liaobaatar changi gen. et sp. nov. Etymology—Liao, after Liaoning Province where the new species is from; baatar, Mongolian, means hero, which has been used as a suffix for generic names of many Asian Cretaceous multituberculates. Diagnosis—As for the type and only species.


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FIGURE 14. Sinobaatar fuxinensis sp. nov., IVPP V14490. SEM photographs (A1, B1) and line drawings (A2, B2) of upper dentitions in occlusal view. A. The left upper dentition. B. The right upper dentition. Scale bar equals 2 mm.

LIAOBAATAR CHANGI sp. nov. (Figs. 18–21; Tables 1, 2) Holotype—Right lower jaw with incisor, p2 to p4, m1 and m2, and fragment of left lower jaw with p2, p3, broken p4, and m1 (IVPP V14489; Figs. 18, 19). Referred Specimens—Fragmentary right lower jaw with broken incisor, p2 to p4 and m1, and isolated broken incisor

fragment (IVPP V14483; Fig. 20); and fragmentary left lower jaw with p3, p4 and m1 (V14500; Fig. 21). Locality and Horizon—Fuxin, Liaoning, northeastern China; Early Cretaceous (Aptian to Albian); the Fuxin Formation. Etymology—In honor of Professor Zhenglu Chang who has contributed great efforts to the geological and paleontological study on the Mesozoic strata in northeastern China.

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FIGURE 15. Sinobaatar fuxinensis sp. nov., IVPP V14490. A. Upper dentitions in left lateral view, a SEM photograph (A1) and a line drawing (A2). B. An X-ray radiograph of right upper cheek teeth. Scale bars equal 2 mm.

Diagnosis—Large eobaatarid multituberculate with quite large p4 in respect to p3, and m1 with cusp formula 2-3:3. Differing from other eobaatarids in its large size and cusp formula of m1. Description—Right and left dentaries, incisors, p3s, p4s, m1s and a right m2 are preserved in the specimens of Liaobaatar changi. Formula of lower dentition is 1.0.3.2. Upper jaw and teeth unknown. Right and left dentaries are preserved in IVPP V14483 and in V14489. The dentary in V14483 is fragmentary, and missing posteriorly the condyle and coronoid process. The right dentary in V14489 is compressed and deformed; the left one is also compressed and its condyle and coronoid process are missing. The dentary is poorly preserved in V14500. In V14483, the anterior part of the lingual side of the dentary is broken, and the exposed incisor reaches posteriorly at least below the p2. The dorsal margin of the dentary is bent dorsally at a low angle anterior to p2, and the incisor points anterodorsally. A mental

foramen in V14489 is situated about 2 mm anterior to the p2 and 2.5 mm above the ventral margin of the left dentary. The horizontal ramus is widest dorsoventrally below p4. The coronoid process extends posterodorsally labial to the m1. The damaged condyle in the right dentary of V14489 is placed below the occlusal level of the molars and facing posterodorsally. The masseteric fossa extends anteriorly below the posterior root of the p4. The pterygoid shelf is preserved along the ventral margin of posterior part of the dentary in V14483. A trace of the pterygoid shelf is preserved in both right and left dentaries in V14489. The broken right lower incisor with its separated apex is preserved in V14483, and a damaged incisor is preserved on the right dentary of V14489. The lower incisor is not very slender but not as robust as those of plagiaulacids and paulchoffatiids. It is not greatly thickened toward its base. It has a rounded labial surface and a more flattened lingual surface, tapering toward the apex. The ventral margin of the lingual surface is slightly swollen. It is completely covered with enamel.


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FIGURE 16. Sinobaatar fuxinensis sp. nov., IVPP V14499. SEM photographs (A1, B1, C1) and line drawings of the cheek teeth region (A2, B2, C2). A. In labial view. B. In lingual view. C. In occlusal view. Scale bar for SEM photographs equals 4 mm, and the one for line drawings equals 2 mm.

The right p2 and both p2s are preserved in V14483 and V14489, respectively. The lower p2 is a tiny, peg-like and nonfunctional tooth with a somewhat swollen crown and leans posteriorly. It is situated immediately anterior to the anterior root of p3 and below the crown of p3. Right p3s are preserved in V14483 and V14489, and left p3s are preserved in V14489 and V14500. The tips of the crown of the right p3 of V14489 and the anteroventral part of the left p3 of V14500 are slightly broken. The crown shape of the p3 is distinctively oval rather than triangular or rectangular in lateral view, and the crown leans posterodorsally. Only one root of the p3, pointing anteroventrally, is visible in V14483 and V14489, whereas it is probable that there is a reduced posterior root. The anterior root is missing in V14500. There are a few tiny serrations accompanied by faint ridges extending anteroventrally. Numbers of serrations are variable among specimens: one in V14483, at least two in V14489, and three in V14500. In V14500, the posteriormost serration is not accompanied by a ridge. The mesioventral part of the crown hangs over the

tiny p2. The height of p3 does not reach to the anterior margin of the p4. Right p4s are well preserved in V14483 and V14489, and left p4s are preserved in V14489 and V14500. The lower p4 is much larger than the p3. The shape of the p4 crown is parallel-sided and roughly rectangular with a slightly arcuate dorsal margin. A modestly U-shaped anterior triangular lobe points ventrally and is small in respect to the crown size in V14483 and V14489, whereas it is larger in V14500 relative to the crown size than the other two specimens of this species. The lower p4 has 11 to 12 serrations. At least ten and probably 11 serrations and nine ridges are present in V14483; the last serration is not accompanied by a ridge. V14489 has 12 serrations, nine of which are accompanied by a ridge, but not the first, 11th and 12th serrations. The labial and lingual surfaces of the p4 of V14489 have an extra ridge on either side. This extra ridge is posteroventral to the ninth ridge, but is not connected with the serrations of the crest. In V14500, there are 11 serrations and ten of them except for the first serration are accompanied by a ridge; the first ridge

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FIGURE 17. Sinobaatar fuxinensis sp. nov., IVPP V14482. SEM photographs (A1, B1) and line drawings (A2, B2) of the right upper dentition. A. In labial view. B. In occlusal view. Scale bar equals 2 mm.

is rather weak and the last ridge on the labial surface is worn. A posterior labial cusp is present near the crown-root junction in V14483 and V14500. That in V14489 is present at approximately half the height of the distal margin of the p4. A wear facet is present dorsal to the posterior labial cusp. This facet is variable; it extends to the 12th serration in V14500, further dorsally beyond the 12th serration in V14489, but not reaching the 12th serration in V14483. The labial side of the p4 does not mirror the lingual side. Right m1s are preserved in V14483 and V14489, and left m1s are preserved in V14489 and V14500. The tooth is slightly asymmetrical with an oblique posterior margin in occlusal view. Cusp formula is 2-3:3. Only two labial cusps are present in V14483, but there are three labial cusps in V14489 and V14500. The first labial cusp is the smallest but well separated from the second one in V14489. It is also the smallest in V14500, and not well separated from the second one. The third labial cusp is long anteroposteriorly in V14489 and V14500. The third labial cusp is ornamented by a groove in the right m1 in V14489, and a groove subdivides the third cusp in the left m1. The first lingual cusp is slightly larger than the second in V14483. It is larger than and as tall as the second one in V14489 and V14450. The third lingual cusp is the smallest. The second and third lingual cusps are not well separated. The lingual cusps are taller than the labial ones. The labial surface of the second lingual cusp is ornamented by a faint groove in V14483.

The right m2 preserved in V14489 is asymmetrical with a strongly oblique posterior margin in occlusal view. Cusp formula is 1 (coalesced):2. The coalesced labial cusp is long anteroposteriorly and resembles a protruding labium. The posterior part of the cusp is taller than the anterior. Its lingual wall is ornamented by grooves and pits. The lingual cusps are subequal in height and the anterior one is slightly larger than the posterior. They are crescentic and face medially. The labial surfaces of the lingual first cusps are ornamented by a groove. Measurements—See Table 1. Discussion—Liaobaatar changi is different from cimolodontans in having the primitive feature of three lower premolars (Kielan-Jaworowska et al., 2004), and is classified as a “plagiaulacidan.” It is clearly distinguished from “plagiaulacidans” except for eobaatarids and Arginbaatar Trofimov, 1980, by a much reduced p3 (Kielan-Jaworowska et al., 2004). The lower p4 of L. changi is roughly rectangular in lateral view, thus distinguishable from cimolodontans and Arginbaatar (Trofimov, 1980; Kielan-Jaworowska et al., 1987; Kielan-Jaworowska et al., 2004). Liaobaatar changi differs from Janumys in the cusp formula of m1 (Eaton and Cifelli, 2001). Eobaatarids and Liaobaatar changi shares p4 characters, such as a more arcuate profile than p4s of plagiaulacids and other primitive “plagiaulacidans” and a much reduced p3 (KielanJaworowska et al., 1987; Hu and Wang, 2002; Kusuhashi, 2008). It also shares the morphology of m2, having only one large


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FIGURE 18. Liaobaatar changi gen. et sp. nov., holotype (IVPP V14489). SEM photographs (A1, B1, C1) and line drawings of the cheek teeth region (A2, B2, C2) of the damaged right dentary with incisor and p2-m2. A. In labial view. B. In lingual view. C. In occlusal view. Scale bar for SEM photographs equals 4 mm, and the one for line drawings equals 2 mm.

coalesced labial cusp, with Eobaatar and Sinobaatar (KielanJaworowska et al., 1987). These dental similarities suggest that L. changi should be assigned to the Eobaataridae. Liaobaatar changi is clearly distinguished from the other eobaatarids by its large size (Table 1). The mean ratios of p4 length and height between L. changi and Sinobaatar xiei (L./S.) are 1.9 and 1.7, respectively. For comparison, the p4 length and height ratios for other eobaatarids are: Eobaatar magnus (PIN 3101-57), 1.8 and 2.0; Sinobaatar lingyuanensis (IVPP V12517), 1.6 and 1.6; Hakusanobaatar matsuoi (SBEI 1736), 1.8 and 1.9; and Tedoribaatar reini (SBEI 1736), 1.7 and 1.7 (Table 1; data of H. matsuoi and T. reini from Kusuhashi, 2008). Liaobaatar changi obviously is the largest among the known eobaatarids. The size of the p4 of L. changi in respect to the p3 is also much larger than other eobaatarids. Liaobaatar changi differs from Eobaatar, S. xiei and S. fuxinensis by possessing three cusps on the lingual row of the m1 (Kielan-Jaworowska et al., 1987).

Liaobaatar changi is clearly distinctive from Loxaulax by many m1 characters (Simpson, 1928; Kielan-Jaworowska et al., 2004). The size of L. changi is clearly too large to be attributed to Monobaatar (Kielan-Jaworowska et al., 1987). Liaobaatar changi is, therefore, erected as a new genus and species of the Eobaataridae, although it can not be compared with a poorly known genus, Parendotherium. Specimens of Liaobaatar changi (V14483, V14489, and V14500) show variability of some characters. In V14483, the p3 has only one tiny serration, whereas at least two and three serrations are present on the p3 of V14489 and V14500, respectively. There are two labial cusps on the right m1 of V14483 instead of three as seen in V14489 and V14500. V14500 has a p4 with a larger U-shaped anterior lobe in respect to the crown size than those in V14483 and V14489. In spite of these differences, we here tentatively assign them to one species, Liaobaatar changi, because there are only three specimens of L. changi up to now,

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FIGURE 19. Liaobaatar changi gen. et sp. nov., holotype (IVPP V14489). SEM photographs (A1, B1, C1) and line drawings of the cheek teeth region (A2, B2, C2) of the damaged left dentary with p2-m1. A. In labial view. B. In lingual view. C. In occlusal view. Scale bar for SEM photographs equals 4 mm, and the one for line drawings equals 2 mm.

and it is difficult to decide whether these differences are intraspecific or interspecific. Family? EOBAATARIDAE Kielan-Jaworowska, Dashzeveg and Trofimov, 1987 Gen. et sp. indet. (Fig. 22; Table 2) Referred Specimen—An isolated right upper premolar (probably P1 or P2; V14506; Fig. 22). Locality and Horizon—Early Cretaceous (Aptian to Albian); the Shahai Formation, Badaohao, Heishan, Liaoning, northeastern China. Description and Comparison—V14506 is an isolated right upper premolar (probably P1 or P2). Although its length is almost as long as P1s and P2s of S. fuxinensis, its crown height is distinctively higher. The bulbous crown of V14506 is compressed labiolingually and has three conical cusps; two in lingual and one in labial. The posterolingual cusp is slightly larger than the others.

A tiny cuspule is present at the base of the posterolabial wall of the labial cusp. The posterior base of the posterior lingual cup is slightly prominent distally. All cusps are ornamented with radiated ridges. The roots are broken and missing. The transversely compressed high crown of V14506 is unique among upper anterior premolars of multituberculates discovered from the Shahai and Fuxin formations. Though V14506 shares a transversely compressed crown with DP1 of Sinobaatar fuxinensis (V14490), this tooth has cuspule, which is not present on DP1 of S. fuxinensis. V14506 also has a higher crown. The size of V14506 indicates that this animal was probably as large as or larger than S. fuxinensis. It is, thus, possibly a tooth of Liaobaatar changi, but it is difficult to conclude because upper teeth of L. changi have yet to be discovered. Other eobaatarid multituberculates have been collected from the Shahai and Fuxin formations (Kusuhashi, Hu et al., 2007), but they are smaller than S. fuxinensis, and V14506 is unlikely to belong to them. Measurements—See Table 2.


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FIGURE 20. Liaobaatar changi gen. et sp. nov., IVPP V14483. SEM photographs (A1, B1, C1) and line drawings of the cheek teeth region (A2, B2, C2). A. In labial view. B. In lingual view. C. In occlusal view. Scale bar for SEM photographs equals 4 mm, and the one for line drawings equals 2 mm.

CONCLUDING REMARKS Three new eobaatarid species of two genera, including one new genus, Sinobaatar xiei sp. nov., S. fuxinensis sp. nov., and Liaobaatar changi gen. et sp. nov., were discovered from the Lower Cretaceous Shahai and Fuxin formations, Liaoning Province, northeastern China. One of the specimens of S. fuxinensis indicates that cheek teeth replacement in eobaatarids occurred in a typical backward sequence seen in Late Cretaceous-Tertiary cimolodontans. Diversified and rich multituberculates from the Shahai and Fuxin formations indicate that multituberculates, which are considered to have migrated from Europe to Asia probably in the early Early Cretaceous, were already flourishing in Aptian-Albian Asian mammalian fauna. ACNOWLEDGMENTS We would like to express our sincere gratitude to Chuankui Li, Shuhua Xie and many other colleagues and technicians of IVPP, and Zhenglu Chang (Investigation Team no. 107, Northeast Coalfield Geological Bureau, Fuxin, China) for their assistance, advice and support of this study. Takehisa Tsubamoto

(Hayashibara Biochemical Laboratories, Inc., Okayama, Japan), Takahiro Takada (Gunma University, Maebashi, Japan), and colleagues of Kyoto University, Kyoto, Japan, gave us critical advice and comments. We appreciate the help and support of Evgeny N. Maschenko (PIN) for our study of specimens in Moscow. Specimen observation in Oklahoma was kindly supported by Richard L. Cifelli, Jeff Person, Brian Davis, and Charles Baker (Sam Noble Oklahoma Museum of Natural History, Norman, USA). Brian Davis also kindly read and corrected the manuscript. Ainara Badiola (University of Zaragoza, Saragossa, Spain) provided us information about European Early Cretaceous multituberculates. SEM photographs were taken at Kyoto University Museum with support of Terufumi Ohno, Masahiro Ichida, Tomohiro Nishimura, and Shin Nunami (Kyoto University). Silicone rubber mold of the specimen was made by Lifen Zhang (IVPP). Thanks are also due to Wending Zhang (IVPP) for taking X-ray radiographs. This paper was greatly improved by comments and advice of two anonymous referees and Zhexi Luo (Carnegie Museum of Natural History, Pittsburgh, USA). During the course of this study, one of the co-authors, Dr. Yaoming Hu, passed away. We wish to pay a special tribute to

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FIGURE 21. Liaobaatar changi gen. et sp. nov., IVPP V14500. SEM photographs (A1, B1, C1) and line drawings of the cheek teeth region (A2, B2, C2). A. In labial view. B. In lingual view. C. In occlusal view. Scale bar for SEM photographs equals 4 mm, and the one for line drawings equals 2 mm.

Dr. Hu for his dedication to the studies of Mesozoic mammals. We also commemorate the victims of a mining accident in a coalmine in Fuxin, where we collected some mammalian specimens from. This study was partly supported by National Science

Fund for Fostering Talents in Basic Research, Special Research Disciplinary Unit (Paleontology and Paleoanthropology), China (J0630965), and Chinese Academy of Sciences Research Fellowship for International Young Researchers. LITERATURE CITED

FIGURE 22. ? Eobaataridae gen. et sp. indet. (IVPP V14506). SEM photographs (A1, B1, C1) and line drawings (A2, B2, C2). A. In labial view. B. In lingual view. C. In occlusal view. Scale bar equals 1 mm.

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