| 1. IntroductionThe materials studied in this book come mainly from the Early Pleistocene Bajiazui fauna in Qingyang County and the Late Pleistocene Loufangzi fauna in Huanxian County, Gansu Province, and partially from other localities. By way of the research to the Chinese fossils of the genus Equus, some new conclusions on the taxonomy, evolution, biostratigraphy, paleoclimatology, chronology and so on about the genus Equus are achieved, which gets better knowledge of the Chinese fossils of the genus Equus and develops applications of mammal fossils on climatic changes. The review and revision to the Chinese fossils of the genus Equus have important theoretic significance. The exploration and discussion of climatic changes on the basis of the genus Equus have effective practical value.Acknowledgements For generous support and assistance to our studying and writing of the present book, we thank Academician Liu Tungsen from Chinese Academy of Sciences, Drs. Qiu Zhanxiang, Xu Qinqi, Wei Qi from Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Drs. Shen Guanglong, Shu Degan, Zhang Yunxiang, Chen Fuguan from Northwest University, Dr. Vera Eisenmann from Museum National d'Histoire Naturelle, Paris, Dr. Ann Forsten from University of Helsinki, Helsinki, Dr. Maria T. Alberdi from Museo National de Ciencias Naturales, Madrid, Dr. Augusto Azzaroli from Universita di Firenze, Firenze, Dr. Bruce J. MacFadden from University of Florida, Gainesville, Academician An Zhisheng, Drs. Zhou Weijian, Li Zhenghua, Liu Rongmo from Xi'an Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences, Drs. Wang Tingzheng, Huang Chunchang from Shaanxi Normal University, Dr. Wu Jiayan from Shaanxi Institute of Zoology, Dr. Yan Jiaqi from Xi'an College of Mining Industry, Dr. Hu Wei from Shaanxi Hydrogeologic Survey, Dr. Zhang Chengjun from Lanzhou Institute of Geology, Chinese Academy of Sciences.2. Systematic Description of the Genus Equus from Bajiazui, QingyangIn 1961, Xue Xiangxu and Wang Yongyan collected a lot of mammalian fossils from Bajiazui of Qingyang County, Gansu Province. The fossils come from the sandy beds in the bottom of the section, including Canis chihliensis, Meles cf. chiai, Hyaena cf. licenti, Megateron sp., Epimachairodus sp., E. cf. crenatidens, Felis sp., Hipparion cf. sinensis, Sus cf. lydekkeri, Megaloceros sp., Cervus sp., Gazella sp., G. cf. sinensis, Bison palaeosinensis, Bovidae indet, Myospalax cf. arvicolinus, and M. tingi, etc. (Wang et al, 1966, 1982). Among the materials there are many skulls, mandibles, cheek teeth and limb bones of the genus Equus. NWUV is the prefix to the vertebrate fossils in Department of Geology, Northwest University.The Early Pleistocene fossils of the genus Equus from northern China were mostly recognized as E. sanmeniensis in the past. However, E. sanmeniensis, a new species determined by Teilhard et al. upon the Nihewan Collection in 1930, is not a single species actually. At that time, they thought that E. sanmeniensis could be divided into two types, large and small. The small type of E. sanmeniensis was determined to be a new species E. teilhardi by Eisenmann in 1975, but its materials were very rare and its distribution was very narrow. The fossil ofE. teilhardi, discovered newly in Bajiazui fauna from Qingyang, Gansu, is described in this book. According to the analysis and comparison of the characters of E. teilhardi, it is considered that E. teilhardi also distributed in Mianchi, Henan and Lantian, Shaanxi. The validity of E. teilhardi is further demonstrated and its distribution is expanded by the new research results.Deng et al. (1999a, 1999b) discovered two new species of the genus Equus from Bajiazui fauna, i. e. E. qingyangensis and E. wangi.Perissodactyla Owen, 1848Equidae Gray, 1821Equus Linnaeus, 1758Equus qingyangensis Deng et Xue, 1999(PI. I ~ V, VT, 2-4, W, 1-4, VfflL 1-4; Tab. 1-6)Holotype NWUV 1128, the middle and back of a skull with all cheek teeth, about 12 years.Referred specimens (1) NWUV 1134, the front and middle of a mandible without right M2.3, male, about 8 years. (2) NWUV 1129, a skull without muzzle, male, (3) NWUV 1130, a skull without occipital region; (4) NWUV 1131, a broken juvenile skull with complete milk cheek tooth rows. (5) NWUV 1132, a broken juvenile skull; (6) NWUV 1133.1, a broken juvenile upper jaw; (7) NWUV 1135, a juvenile mandible without muzzle; (8) NWUV 1132.2, a juvenile mandible without ascending ramus. Other specimens include 8 upper and 14 lower fragmental jaws with cheek tooth rows, 7 fragmental muzzles, 35 upper and 15 lower isolated milk cheek teeth, 8 isolated incisors, and a lot of limb bones. All specimens are preserved in Department of Geology, Northwest University.Diagnosis Middle size. The nasal notch extends above the back of P2. The praeorbital pit is shallow with an indistinct border. A deep groove is along the nasal suture. The upper teeth havelong protocones and weak pli caballine. The lower teeth have typical V-shaped linguaflexids and deep ectoflexids that penetrate into the isthmuses even touch the linguaflexids on the lower molars. The limb bones are slender. The metacarpal middle shaft index is smaller than 13.5 and the metatarsal smaller than 12.0. It was the early species of Equus with the most slender limb bones in Eurasia.Distribution Northwestern and northern China.Age Nihewanian, Early Pleistocene.Description Skull: the intercondyloid notch is narrow. The paramastoid process is robust. The basilar tubercle is rough and lightly projecting. The pterygoid canal is in the temporal wing near the sphenoid bone. The pterygoid process is very high but the postforamen of pterygoid canal can be seen in ventral view. The frontal surface is level and smooth as well as very wide, and it lightly inclines laterally from the postorbital constraction. The supraorbital foramen and the upper orbital margin are lightly lower than the frontal surface. There is a notch in the front of the extrafrontal crest. The anterior end of the zygomatic process of the temporal bone reaches the half of the orbit, and the zygomatic process is relatively low in the skull. The temporal condyle is transversally oval and lightly projecting outwards, and its position is the widest in the skull. The glenoid cavity is deep in the middle and becomes shallow in the interior. The temporal crest is robust and strong. The facial crest is much projecting and its anterior end extends above the mesostyle of P4. The praeorbital pit is shallow with an indistinct border. The alveolar tuber is great and the maxillary tuberosity is round. The maxillary recess is big and deep. On the palatine process, the palatine sulcus develops from the level before P4 and becomes deep postwards till reaches the anterior palatine foramen in the level after the protocone of M3. The canine alveole is strongly projecting outwards so that this position is the widest in the muzzle. The center of the posterior margin of the palate is in the level before M3. The pterygoid bone is very thin and opens behind. A deep groove is along the nasal suture. The nasal side surface is steep and top surface is wide. The nasal notch extends above the back of P2. A small lacrimal tabercle is on the upper front of the orbit. The facial length of the lacrimal bone is much longer than the half of the orbit. The zygomatic process of the zygomatic bone goes beyond the orbital posterior border and reaches the front of the temporal fossa. The vomer notch is a deep curve.Mandible: The bone is thick, and its lingual surface is smooth and spoon-shapedly concave while the mental surface is swelling and rough. The suture of the symphysis is distinct. The external surface of the horizontal ramus is smooth and swelling vertically. The mental foramen is on the lower middle of the diastema. The lower margin of the horizontal ramus is flat and straight as well as thick and round. The vasorum notch is in the behind 1/3 of the horizontal ramus. The angle of the mandible is thick with a rough lip and becomes thin upwards. The condyloid process is strongly declined forwards down.Upper cheek teeth: dP1 exists generally. The anterstyle of P2 is small. The premolars have wide and short protocones with weak middle grooves, large parastyles with flat tops inclined forwards, wide and middle-grooved mesostyles, weak pli caballine, and short and wide hypocones.The molars have narrow para- and mesostyles, deeply middle-grooved protocones, no pli caballine, narrow and long hypoconal grooves, simple enamel plications, and inclined protolophes and metalophes. The M3 has a double-angle posterior margin, a narrow and long protocone, and an isolated enamel lake.Lower cheek teeth: The paraconid of P2 is strongly projecting with a round end. The lower premolars have protostylids, developed pli caballinid, short ectoflexids, round metaconids with handles, metastylids with sharp posterior angles, and approximately square entoconids. The lower molars have small pli caballinid, square metaconids with handles, very small metastylids, oval entoconids, and deep ectoflexids that penetrate into the isthmuses and touch the linguaflexids so that the bottoms of the ecto- and linguaflexids become flat. All of the lower teeth have V-shaped linguaflexids and swelling bottoms of the pre- and postflexids. The M3 has a narrow and long entoconid and a large hypoconulid that is strongly projecting postwards.Third metapodials: The limb bones of E. qingyangensis are very rich, but the most representative metapodials are discussed in this paper because of the limited space. The distal ends of the second and fourth metacarpals reach the position between the 1/2 and lower 2/3 of the third metacarpal. A nutrient foramen is on the upper 1/3 of the McIII. On the proximal end of McIII, the articular facet for the Os carpale IV is a long inverse trapezium that has a 190° front angle and a 180° back angle with the articular facet for the Os carpale III. The position of the nutrient foramen of the third metatarsal is relatively higher. On the proximal end of the MtUI, the central depression is rough and the external notch is deep. The front angle between the articular facets for the Os tarsi Hand III is 145° . The front angle between the articular facets for the Os tarsi III and IV is 190° . The distal sagittal crests of the McIII and MtUI are lower ahead than behind. The metapodials of E. qingyangensis are very slender.Comparison and discussion E. qingyangensis has obvious differences from E. sanmeniensis on their teeth. Firstly, the tooth size of E. qingyangensis is smaller than or at most equal to the lower limit of E. sanmeniensis from Nihewan (Teihard et at, 1930; Forsten, 1986), and smaller than that of E. sanmeniensis collected mainly from Mianchi County, Henan Province by Zdansky (1935). Liu (1973) considered that E. sanmeniensis from Zhoukoudian is lightly smaller than that from Nihewan, but its tooth size is still larger than that of E. qingyangensis. Secondly, the pli caballine of E. qingyangensis are not developed. Except young individuals, the pli caballine of E. qingyangensis are very weak or even absent in the adult. On the other hand, the pli caballine of E. sanmeniensis are well-developed on its premolars and very marked on its molars generally. For example, on the specimen of Teilhard et al. (1930, PI. VI, 4), the pli caballine are very well-developed on its premolars and molars. On the specimen of Liu (1973, PI. I , 2), the pli caballine are rather well-developed or at least very marked on the whole tooth rows. Only in the lightly worn specimen of NWUV 1129, E. qingyangensis has obvious pli caballine. Thirdly, the development of pli caballinid is relevent to the worn degree, however, the pli caballinid frequences of E. qingyangensis are higher than those of E. sanmeniensis, which can be regarded as a difference between their lower teeth.The pli caballinie of E. stenonis, distributed widely in Eurasia, are very weak or absent like E. qingyangensis (Eisenmann, 1980, PL XVffl XIX). However, the protocones of the former are shorter than those of the latter. The roots of metaconids of E. stenanis contract strongly so that become narrow necks (Azzaroli et al, 1993, PI. IV, 2), while those of E. qingyangensis reduce postwards gradually but do not form obvious necks.The materials of E. huanghoensis are very rare, only including some isolated upper cheek teeth (Chow et al., 1959), however, their large sizes and wide-short protocones are different from the middle sizes and narrow-long protocones of E. qingyangensis. The tooth size of E. yunnanensis is similar to that of E. qingyangensis (Colbert, 1940; Liu et al., 1974), but the former ectoflexids do not penetrate into the isthmuses while the latter penetrate or touch the linguaflexids. E. teilhardi lacks of cups on its lower incisors(Eisenmann, 1972). On the contrary, all incisors of E. qingyangensis have complete cups.The skull of E. qingyangensis is smaller than that of E. sanmeniensis. A skull of E. sanmeniensis from Nihewan is very large because its vertex length is 6S0 mm and its basilar length is 585 mm(Teilhard et al., 1930). The basilar length of E. sanmeniensis from Qixian, Shanxi is 522 mm (Zdansky, 1935). On the other hand, the basilar length of E. qingyangensis is about 509 mm (Tab.l).The limb bones of Equus have a very important significance for the determination of different species. The greatest length of the McIII of E. qingyangensis is between those of E. sanmeniensis (255~283 mm, Teilhard et al., 1930) and E. teilhardi (213~220 mm, Eisenmann, 1975), and similar to that of E. sanmeniensis from Zhoukoudian (Liu, 1973). But the McIII of E. qingyangensis is more slender than those of all known stenonid horses because its middle shaft index is 13.3 (Tab. 10) while that of E. stenonis in Europe is 14.9—16.3 (Eisenmann, 1979), E. sivalensis in Asia is 14.3—14.9, E. sanmeniensis is 14.8~16.1 and E. teilhardi is 14.6—15.5, the fossils of Equus from Ceyssaguet in France is 14.3~15.2 (Teilhard et al., 1930), E. sanmeniensis from the localities of northern China is 14.4—16.3 (Zdansky, 1935) and from the localities of Zhoukoudian is 15.1-16.8 (Zdansky, 1928; Teilhard, 1936; Teilhard et al, 1941; Liu, 1973), E. conversidens in North America is 13.8~16.3 (Daiquest, 1967). Correspondingly, the middle shaft index of the MtUI of E. qingyangensis is 10.9—11.9 (Tab. 11) and smaller than those of other stenonid horses because those of E. sanmeniensis is 12.5~15.5 and E. teilhardi is 12.5 from Nihewan, Equus from Ceyssaguet is 15.3, E. sanmeniensis from the Locality 9 and 13 of Zhoukoudian is 13.4 ~ 13.7, E. stenonis in Europe is 13.0—14.0 (Eisenmann, 1979), E. simplicidens is 12.7 — 14.0 (Azzaroli et al., 1993), E. conversidens is 11.9 ~ 12.8, and E. niobearensis is 13.3 in North America (Daiquest, 1967). Only the lower limits of E. sanmeniensis from the localities of northern China (11.5—12.9, Zdansky, 1935) and from the Locality 1 of Zhoukoudian (11.4—13.5, Liu, 1973) are close to the upper limit of E. qingyangensis. To sum up, this species has very slender metapodials and is much different from other Early Pleistocene species of Equus in Eurasia and North America.Equus wangi Deng et Xue, 1999(PI. K, 1~2; Tab. 7-8)Holotype NWUV 1170, complete upper and lower cheek tooth rows that belong to an individual, and the upper tooth rows go with the remains of the maxillae, about 5 years.Diagnosis The teeth are very large. The length of the upper cheek tooth row is 195 mm and the lower is 196 mm. The dP1 exsits. The protocones are long, narrow and middle-grooved. The mesostyles are flat or lightly middle-grooved. The enamel plications are strong, especially on the premolars. The hypoconal grooves on the premolars have flat bottoms. The M3 has a double-angle back margin and an enamel lake within its hypocone. The double-knots are very circular so that its metastylids do not have posterior angles. The linguaflexids are wide and sharply V-shaped. The ectoflexids are shallow so that they never penetrate into the isthmuses even on its molars, and the postflexids are long correspondingly. The pli cabalUnid are much developed. The enamel plications of the postflexids are strong. The entoconids on its premolars have sharp beak-shaped ends. The hypoconulid on its M3 likes a short dagger with a wide and round end.Distribution Only Qingyang, Gansu so far.Age Nihewanian, Early PleistoceneDescription A very small dP1 is preserved on the front of the left upper cheek tooth row, which indicates that dP1 exist in adult individuals of E. wangi. The right dP1 of this specimen is lost.P2: The anterostyle is approximately square, and it has a flat end and a small plication on the lingual margin of its bottom. The protocone is short and projecting postward. The postprotoconal valley is shallow and the pli caballine is big. The mesostyle is wide and middle-grooved, and it lightly inclines forward. The hypocone is sharp and the hypoconal groove is obliquely square. The enamel plications of the prefossete are developed. The pli protoloph is strong; the pli prefossette are fine and close; the pli postfossette are fewer and the pli hypostyle is moderate. The pli protoconule from the P2 to the M3 are robust and have branching ends.P3: The post protoconal valley is wide and deep. The pli caballine is big. The parastyle is wide and has a flat top inclined forward. The mesostyle has a neck. The hypocone is sharp and the hypoconal constriction is obvious. The hypoconal groove is wide and deep. The pli protoloph, postfossete and hypostyle are moderate. The pli profossete are fine and close . The protoloph and metaloph are oblique. The protocone from the P3 to the M3 are narrow and middle-grooved, and they have sharp anterior and posterior ends.P4: It is similar to the P3, only its protocone is longer and its hypoconal groove is shorter.M1: The parastyle is sharp and the mesostyle is square. The hypocone is small and parallel to the tooth longitudinal axis. The hypoconal groove is deeply V-shaped. The enamel plications are weak. The anterior and posterior angles of the prefossete are strongly projecting outward. The protoloph and metaloph are oblique. The postprotoconal valleys are narrow and deep, and the pli caballine are small on the all molars.M2: It is similar to the M1, only its parastyle is square.M3: The protocone is very long and its neck inclines forward. The postprotoconal valley is parallel to the tooth longitudinal axis. The parastyle is sharp and the mesostyle is low. The posterior margin of the tooth is concave so that the metastyle and the hypocone become two angles projecting postward. There is an enamel lake within the hypocone. The enamel plications are simple, only pli prefossete are rich.P2: The parastylid is strongly projeting forward. There is a small plication on the posterior wall of the isthmus. The ectoflexid is wide and the pli caballinid is big. The enamel plications of the postflexid are strong. The entoconids on the all premolars is big and beak-shaped. The double-knots are circular, and the linguaflexids are shallow and sharply V-shaped from the P2 to the M3.P3: There is a weak protostylid. The isthmus is perpendicular to the tooth longitudinal axis. The hypoconulid occupies the half width of the posterior margin of this tooth. The hypoconid is long. The pli caballinid is big and robust. The ectoflexids is narrow. The enamel plications of the postflexids are stronger than those on the P2.P4: It is similar to the P3, only its metastylid has a short handle and the hypoconid has a concave external wall.M,: The entoconid is square. The hypoconulid is a small delta. The pli caballinid is short. The end of the ectoflexid is close to the external border of the isthmus. The enamel plications of the postflexid are weak and the neck of the postflexid is approximately perpendicular. The each metastylid on the all molars has a short handle.M2: It is similar to the M,, only the metastylid is smaller, the hypoconulid is bigger, and the ectoflexid is more shallow.M3: The isthmus is perpendicular. The entoconid is oval. The hypoconulid is strong projecting postward, and it has a round end, a narrow root like a neck, and a high plications on each side, as a result, the hypoconulid likes a short dagger with a wide end. The bottom of the preflexid is a trapezoid swell. The enamel plications of the postflexids are very sharp. The pli caballinid is small. The ectoflexid is shallow and does not penetrate into the isthmus.Discussion Because the linguaflexids of E. wangi are typically V-shaped, this species belong to the stenonid. However, some of its characters are obviously different from those of the other stenonid horses in Eurasia and North America, especially its characters on the lower cheek teeth.The tooth size of E. wangi is within the variation limit of E. sanmeniensis (Teilhard* et al., 1930; Forsten 1986, Tab. 1), but the tooth structures of these two species have great differences. The enamel plications on the upper teeth of E. wangi are much stronger and richer than those of E. sanmeniensis. The average plications of E. wangi is 10.3 on each tooth while E. sanmeniensis is 5.6 according to the statistics of Forsten (1986). E. wangi has both strong plications with branching ends as well as fine and close ones on its premolars. The differences between these two species are more evident on their lower cheek teeth. Firstly, E. sanmeniensis from Nihewan has triangular metastylids with very sharp posterior angles (Teilhard et al., 1930, PL W, 4). E. sanmeniensis from Zhoukoudian also has metastylids with sharp posterior angles (Liu 1973, Fig. 3). On the other hand, E. wangi has very circular double-knots, e.g. its P4 has a complete regular circular metastylid andall metastylids do not have projecting posterior angles, which are much different from E. sanmeniensis. Secondly, the ectoflexids of E. sanmeniensis are deep and penetrate into the isthmuses on its molars so that the bottoms of the lingua- and ectoflexids become flat, which is an important character for many stenonid horses. On the contrary, the all ectoflexids of E. wangi never penetrate into the isthmuses, e.g. its deepest ectoflexids on the M, and M3 only approach the external borders of the isthmuses. Thirdly, the M3 ofE. wangi has a distinctive short dagger-shaped hypoconulid.The size of E. wangi is obviously larger than that of E. qingyangensis. The pli caballine and enamel plications of the former are stronger and richer than those of the latter. The big and circular metastylids of E. wangi are easily distinguished from the small and sharp ones of E. qingyangensis. The latter has very deep ectoflexids (Deng et al., 1999a).E. wangi has some characters in common with E. yunnanensis because both of them have circular metastylids and shallow ectoflexids (Colbert 1940; Liu et al., 1974). However, E. wangi is larger than E. yunnanensis, and the latter does not have strong enamel plications and a dagger-shaped hypoconulid on its M3 (Pei, 1961).E. wangi has a similar cheek tooth size to E. huanghoensis, but the very long protocones of E. wangi are different from the very short ones of E. huanghoensis ( Chow et al, 1959). Among the early species of Equus in Europe, E. stenonis from Seneze is the closest to E. wangi because the former has relatively shallow ectoflexids and obtusely triangular metastylids (Eisenmann 1981, PI. IV, 2). But its simple and weak enamel plications of the postflexids are different from the strong and big ones of E. wangi. The size of E. stenonis from Seneze is smaller than that of E. wangi because the lower tooth row's length of the former is 185 mm while the latter is 196 mm. The each upper cheek tooth of E. stenonis has weak enamel plications and a very short protocone without a middle groove (Eisenmann 1980, PI. XIX, 2,4), which are very different from E. wangi.E. wangi is similar to E. simplicidens from Hagerman, Idaho on some important characters, e.g. E. simplicidens also has very circular double-knots, beak-shaped premolar entoconids and sharp V-shaped linguaflexids (Gazin 1936, PI. X X Vffl; Azzaroli et al, 1993, PI. II, 2). But there are differences between these two species. Firstly, the ectoflexids of E. simplicidens penetrate into the isthmuses and touch the linguaflexids so that the postflexids become short correspondingly on its molars. Secondly, the enamel plications on the lower teeth of E. simplicidens are very simple. Thirdly, E. simplicidens has smaller tooth sizes and shorter protocones without middle grooves.E. simplicidens was the earliest species of Equus and the age of the Hagerman fauna was about 3.4 Ma B.P. (Lindsay et al, 1984), therefore, its circular double-knots represented a primitive character. Evidently, E. wangi retained the primitive circular double-knots. On the other hand, E. wangi has very shallow ectoflexids, which are considered to be an advanced character (Eisenmann et al, 1988). As a result, E. wangi was the most advanced one of the closet descendants of E. simplicidens.Short dagger-shaped hypoconulids on M3 like that of E. wangi are not found in the other fossil species of Equus. However, the hypoconulid on the M3 of the modern E. grevyi in Africa issomewhat similar to that of E. wangi (Eisenmann 1981, PI. 1, 1), which implies there may be a certain relationship between them.3. Systematic Description of the Genus Equus from Loufangzi, HuanxianBy means of a deepgoing research for the fossils of the genus Equus in the Loufangzi fauna in Huanxian, Gansu, the corrections about identifmg standards and distingushing principles between E. hemionus and E. przewalskii. It is negated that the ectoflexids on the lower molars of E. hemionus do never penetrate into the metaconid-metastylid isthmuses and the widthes of the upper cheek teeth (P2~M2) of E. przewalskii are always larger than their lengthes. It is proved that these two features only have a statistical sense and are not regarded as identifing standards,especially for isolated cheek teeth. On the basis of mathematical statistics, it is proved that the variation scopes of the cheek tooth sizes of E. hemionus and E. przewalskii can be discovered to occupy different distributions although they have mutually overlaps. There are very obvious differences on the size, proportion and structure of the limb bones between E. hemionus and E. przewalskii.The differences on the cheek teeth of E. hemionus and E. przewalskii follow:(1) The cheek tooth size of E. hemionus are smaller than those of E. przewalskii;(2)The pli caballin of E. hemionus do not develop well or are absent while those of E. przewalskii develop well;(3)The protocone lengthes and idexes of E. hemionus are smaller than those of E. przewalskii;(4)The double knots of E. hemionus is generally between stenonid and caballoid, its metaconid is a round with a long neck. On the other hand, the metaconid of E. przewalskii is approxmately a round with a long neck but its metastylid expands posteriorly to be a long triangle.(5)The linguaflexids of E. hemionus is V-shaped or between V-shaped and U-shaped while those of E. przewalskii are widely U-shaped.4. Systematic Description of New Materials from Other LocalitiesThe fossils of the genus Equus are descriped mainly from three localities, namely Dali, Weinan, Xunyi where are located in Shaanxi Province. The materials include a mandible, some cheek tooth rows, isolated cheek teeth, limb bones and no skulls.It is considered that the diagnosis of E. sanmeniensis should be according to the specimens from Nihewan of Teilhard and Piveteau in 1930. The corrections about free falsifications to the diagnosis of E. sanmeniensis are made, and the published distributions of E. sanmeniensis in northeastern China are negated.E. huanghoensis is a Lower Pleistocene species of the genus Equus from China, however, its materials were very rare when it was determined to be a new species by Chow and Liu in 1959, and its geographical distribution was rather limited, as a result, some authors doubt its validity as an independent species. On the basis of the research to the fossils of E. huanghoensis discoveredrecently from Xunyi, Shaanxi as well as the detailed comparison with E. sanmeniensis, E. stenonis, E. livenzovensis from Eurasia and E. simplicidens from North America, the characters of E. huanghoensis are proved to be stable and different from the other Lower Pleistocene species of the genus Equus. Therefore , E. huanghoensis is determined to be a valid species. The new discovery of E. huanghoensis expands its geographical distribution.The existence off. kiang is firstly determined in the Chinese fossil horses of the genus Equus. E. kiang is separated out of the former vague wild Asian asses, which provides a new fossil evidence for the explanation of distinct climatic types because E. kiang lives in a cold and damp environment different from the cold and dry one of E. hemionus.5. Review and Revision of the Some Chinese Fossil Species of the Genus EquusThe distribution of E. stenonis in China is affirmed. It is proved that the origin center of E. stenonis may be in China, because E. stenonis in the Xinyaozi fauna in Tianzhen, Shanxi Porvince is older than that in Europe and North America.E. yunnanensis is a close relative ofE. wangi lived in north. They are all derived directly from a primitive ancestor of the genus Equus in North America. They retain some common primitive features as well as evolve some distinct adaptive features in different ecological environments.The partial diagnosis of E. beijingensis is revised. The view point is negated that E. beijingensis is the ancestor of E. caballus and it is considered to be more primitive only than E. przewalskii and E. dalianensis.Limb bones are important for the identification and distinction on the different species of the genus Equus, as a result, E. dalianensis is deeply convinced a valid species on the basis of its limb bone proportions and sizes different completely from those of E. przewalskii, although the skulls and cheek teeth of the two species are very similar.E. caballus is revised, especially a lots of fossils of E. cf. caballus in the Yushu fauna in northeastern China should belong to different species of the genus Equus. There are earlier fossils of E. caballus in Heshui, Gansu.There are four invalid species in the Chinese fossils of the genus Equus, among which E. leptostylus is an abandoned name, E. cautleyi is the synonym of E. sivalensis as well as is absent in China, E. wuchengensis is a naked name, and E. ferus is the early synonym of E. przewalskii but a forgotten name.So there have been 13 valid species in the Chinese fossils of the genus Equus. They include: Equus sanmeniensis Teilhard et Piveteau, 1930 Equus teilhardi Eisenmann, 1975 Equus huanghoensis Chow et Liu, 1959 Equus yunnanensis Colbert, 1940 Equus stenonis Cocchi, 1867 Equus qingyangensis Deng et Xue, 1999Equus wangi Deng et Xue, 1999Equus beijingensis Liu, 1963Equus dalianensis Chow et al., 1985Equus pnewalskii PoUakov, 1881Equus caballus Linnaeus, 1758Equus hemionus Pallas, 1774Equus kiang Moorcroft, 1841According to the morphologies and measurements of their skulls, cheek teeth and metapodials, the characteristic polarities of the Chinese fossils of the genus Equus are determined. Four index tables are formulated about the skulls, upper cheek teeth, lower cheek teeth and metapodials of the all 13 valid species of the Chinese fossils of the genus Equus. The skull index of the Chinese species of the genus Equus follows:A. Shallow praeorbital pit; deep longitudinal furrow along nasal suture........................BNo praeorbital pit; no longitudinal furrow along nasal suture.................................HB. Large size; basilar length longer than 520 mm; cheek teeth length longer than 190mm ...................................................................................................CMiddle size; basilar length about 500 mm; cheek teeth length about 180 mm ............FC. Deep nasal notch which extends above mesostyle of P3; narrow and long nasal freepart ...................................................................................................DShallow nasal notch which extends above mesostyle of P2; wide and short nasal free part ????'............................................................................E. sanmeniensisD. Narrow and long protocone with...
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