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Cimolodonta (Kielan-Jaworowska, Dashzeveg, and Trofi-mov, 1987, see chapter 8). Gobiconodon, a eutriconodon-tan genus shared with the Cloverly Formation of North America (among others elsewhere) and thus implying some degree of interchange among continents, is represented by two species (Trofimov, 1978; Kielan-Jaworowska and Dashzeveg, 1998). Other noteworthy elements of the fauna include a "symmetrodontan" (Trofimov, 1980, 1997), one or two peramurid-like "eupantotherians" (Dashzeveg, 1979,1994), and Kielantherium, a remarkably primitive boreosphenidan that may be related to Delta-theroida (Dashzeveg and Kielan-Jaworowska, 1984). Last but certainly not least, Hoovor has yielded one of the earliest generally accepted eutherians, represented by both upper and lower dentitions, Prokennalestes (see Belyaeva et al., 1974; Kielan-Jaworowska and Dashzeveg, 1989; Si-gogneau-Russell et al., 1992); a petrosal has also been referred to Prokennalestes (Wible et al., 2001).

Another locality in Mongolia, Khamaryn Us (figure 2.12), is in the Khukhtyk or Dzunbain Formation. It apparently was discovered in 1977 and is thought to be of the same age as Hoovor, that is, Aptian-Albian (Tumanova, 1987). The fauna includes Psittacosaurus, a variety of other dinosaurs, and varanoid lizards. An "amphilestid" mandible with m2-3 has apparently been collected at Khamaryn Us (Reshetov and Trofimov, 1980; Averianov, 2000).

The locality of Oshih (Aishle), long known for its assemblage of Early Cretaceous dinosaurs (e.g., Osborn, 1923), has recently yielded fossil mammals (see Rougier et al., 2001, chapter 7). Two species of Gobiconodon are represented at Oshih: G. hopsoni (known by fragments of the maxilla and dentary), which is as large or larger than North American G. ostromi, and an apparently new species (known by two dentary fragments, possibly belonging to the same individual), similar in size to G. borissiaki, known from Hoovor and elsewhere.

China

Early Cretaceous mammals, as yet mostly unidentified, have been discovered at four sites in Inner Mongolia, China (figure 2.12): Elesitai, Laolonghuozi, Hangjin Qi, and Yanhaizi. Elesitai is in the Bayan Gobi Formation, locally made up of claystones, mudstones, and sandstones. The modest fauna, said to include psittacosaurs, is thought to be of Aptian-Albian age. The mammalian specimen, as yet underscribed, is a well-preserved lower jaw with three teeth (Dong, 1993; Lucas and Estep, 1998; Averianov and Skutschas, 2000a).

The remaining three sites (Averianov and Skutschas, 2000a) are all near Hangjin-Qi and are in the Eijinhoro Formation (synonymous with the Luohandong For mation). Laolonghuoze is 30 km west of Hangjin-Qi. The herpetofauna includes an atoposaurid crocodilian (Wu et al., 1996); a mammalian humerus has been collected from the site (Dong, 1993). Yanhaizi has yielded a maxilla of an unidentified mammal (Averianov and Skutschas, 2000a). Hangjin-Qi is the source of a mandible described as belonging to an "amphilestid" mammal, Hangjinia chowi (see Godefroit and Guo, 1999). Though the tooth crowns are broken off, X-rays show that molariforms were replaced, as they were in Gobiconodon (see chapter 7).

Early Cretaceous mammals have recently been reported, though not yet described, from the Mazongshan area, Xinmingbao Group (= Chi-Jin-Bao Group), Gansu Province (figure 2.12). Mammalian fossils have been collected from at least two sites in the lower part of the unit (lower Red Beds and middle Gray Beds). Combined sedi-mentologic and paleontologic data suggest a fluviolacus-trine depositional setting and paleoclimatic conditions that were semiarid and subtropical (Tang et al., 2001). The lower part of the Xinmingbao Group is estimated to be of Barremian-Albian age, based on invertebrates, vertebrates, plant macrofossils, and palynomorphs (Tang et al., 2001; see also Chow and Rich, 1984b; Averianov and Skutschas, 2000a). All mammalian fossils collected to date reportedly represent a new taxon of Gobiconodontidae (Tang et al.,2001).

Xinjiang Autonomous Region is home to at least one occurrence of an Early Cretaceous mammal (Chow and Rich, 1984b). The locality, Huang-Ni-Tan (figure 2.12), is in the Ke-la-mei-li area of the Junggur Basin. The fossil, consisting of a dentary with five broken teeth belonging to an unidentified mammal, is from the Lower Cretaceous Shengjinkou Formation, Tugulu Group. Another site in Xinjiang Region, Jianshan Wash, was noted earlier under Late Jurassic. The described taxon from this site, Klamelia, is an "amphilestid triconodont" that is rather similar to Early Cretaceous Gobiconodon, suggesting the possibility that Jianshan Wash may eventually prove to be of Early Cretaceous age as well. The upper stratigraphic constraint of the site is reported to consist of horizons referable to the Upper Cretaceous (Chow and Rich, 1984a).

The majority (as well as the most spectacular) of Early Cretaceous mammal occurrences in China are from Liaoning Province. The mammal-bearing sequence lies in the Jehol Group. The basal unit of the Jehol Group is the Yixian Formation, which is mainly lacustrine, with inter-bedded volcanic tuffs and lavas. Beds 6 and 8 of the Yixian Formation (see Wang, Wang, et al., 1998) have yielded mammals. A radiometric date of 124.6 Ma (Swisher et al., 1999) from an underlying horizon (bed 4) is believed to closely approximate the age of the Yixian mammals, placing them in the middle Barremian. Overlying the Yixian

Formation is the Shahai Formation.7 The Shahai Formation includes a mixture of coal, fluvial, and lacustrine deposits. The age of the Shahai Formation, from which mammals are also known, is not well understood. Given the radiometric dates from the underlying Yixian Formation, the mammals of the Shahai Formation must be younger than middle Barremian—perhaps much younger. We tentatively regard it as Aptian. The Fuxin Formation, in turn, overlies the Shahai Formation. The Fuxin Formation consists of coals, sandstone, and sandy conglomerates (Wang et al., 1995). Like the rest of the Jehol Group, this unit was at one time considered to be of Jurassic age (e.g., Yabe and Shikama, 1938), but is now referred to the Lower Cretaceous. Age estimates for the Fuxin Formation range from Barremian-Aptian (Nessov, Sigogneau-Russell, and Russell, 1994), to an upper limit of Aptian (Wang et al., 1995), to much younger. We tentatively regard it as Aptian-Albian and suspect that it may eventually prove to be younger, perhaps early Late Cretaceous. As noted earlier, the "symmetrodontan" Manchurodon, from the Zhadyzhao Mine, was incorrectly ascribed to the Fuxin Formation and may well be of Jurassic age.

The most remarkable newly discovered Early Cretaceous mammals are, without doubt, those from the Yixian Formation (see the review of stratigraphic sequence and fossil horizons by Wang, Wang, et al., 1998). To date, mammalian fossils have been reported from four sites in this unit. Three are especially noteworthy: the "symmetrodontan" Zhangheotherium quinquecuspidens, from the Jian-shangou Valley (bed 8); the "triconodont" Jeholodens jenk-insi, from the nearby site of Sihetun (bed 6) (Hu et al., 1997,1998; Ji et al., 1999); and the eutherian Eomaia scan-soria, from the Dawangzhangzi locality, farther to the west (Ji et al., 2002). All three are represented by specimens that, though flattened, are breathtaking in their completeness, including the skull and skeleton (the holotype of Eomaia scansoria also includes remnants of some soft tissues, such as costal cartilages and fur). The Dawangzhangzi locality has also yielded the partial skull and skeleton of the eobaatarid multituberculate, Sinobaatar lingyuanensis (see Hu and Wang, 2002a,b).

The basal member of the Yixian Formation has yielded mammalian fossils from near the village of Lu-Jia-Tun. Skulls with articulated mandibles, together with some postcranial remains, are known for two taxa: Gobiconodon (reportedly represented by a new species) and its apparent close relative Repenomamus (Li et al., 2000,2001; Wang et al., 2001b).

7 Some workers (e.g., Wang et al., 1995) separate the Shahai Formation into the Shahai, sensu stricto, and the underlying Jiu-Fuo-Tang Formation.

The principal site in the Shahai Formation is Badao-hao, Heishan (figure 2.12), from which at least five mammalian taxa are known (Wang et al., 1995). Two "pla-giaulacidan" multituberculates are present. One of these is similar to Albionbaatar, otherwise known from the Berri-asian of England; the other is a plagiaulacid, represented by a dentary. Other taxa from Badaohao include a "sym-metrodontan," an extremely primitive, aegialodont-like boreosphenidan, a possible eutherian (Wang et al., 1995; see also Averianov and Skutschas, 2000a), and an unspecified type of "triconodont."

Two sites in the Fuxin Formation (sometimes referred to in older literature as the "Husin Series" [see Clemens et al., 1979]) have yielded mammals (figure 2.12). Endo-therium, a probable eutherian represented by jaw and associated postcranials (Shikama, 1947), is from the Xinqiu (Hsinchiu) Mine in the Fuxin Formation. The specimen was unfortunately lost during World War II, but illustrations suggest a rather advanced morphology. A single tooth of an unidentified multituberculate is known from a similar horizon at another locality, near Xindi (Wang et al., 1995).

Japan

Discoveries of two Early Cretaceous mammals in Japan have been reported, though neither has yet been described. The fossil occurrences, at Kaseki-kabe in Ishikawa Prefecture (figure 2.4), are in the Kuwajima Formation and are believed to be of late Hauterivian age. One specimen is a dentary bearing molars of "amphilestid" design (Rougier et al., 1999) and the other is a dentary (bearing one tooth, p4; another tooth of uncertain identity may be associated) of an eobaatarid-like multituberculate (Takada et al., 2001).

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