秦岭东段李官桥盆地始新世哺乳动物化石新材料

THE NEW MAMMALIAN MATERIALS FROM THE EOCENE OF LIGUANQIAO BASIN

李官桥盆地是始新世地层发育较全、哺乳动物化石丰富的盆地。本文报道了该盆地两个始新世化石新地点,哺乳动物共计4目7属8种。其中有5个新种,分别为Kuanchuanius? danjiangensis sp. nov.、Asiocoryphodon progressivus sp. nov.、Gobiatherium minutunz sp. nov.、Lophialetes? primus sp. nov.、Eomoropus? zhanggouensis sp. nov.。动物群的时代可能为中始新世早期。

Liguanqiao basin of southwest Henan Province is one of the Mesozoic and Cenozoic basins in the eastern Qinling Mountains, and is also one of the important basins in studying Mesozoic and Cenozoic biostratigraphy of China. Since Chu and Li in 1929 first reported the vertebrate fossils from the basin, geologists have made much progress in stratigraphy and paleontology. Besides a great number of Eocene fossil mammals have been discovered. It provides important evidence for the subdivision of the strata in the basin based on the previous works at present, its strata are divided into Hugang Formation (late Cretaceous), Yuhuangding Formation (early-middle Eocene), Dacangfang Formation (Middle Eocene), Hetaovuan Formation and Fenghuangchen Formation (Neogene). This paper describes the fossil mammals from the two new localities in the basin. One (Loc. 84003) is situated at 500 m east of Zhanggou Village; the other (Loc. 86001) 100 m west of Zhanggou Village. The specimens collected can be assigned to eight taxa. Tillodontia Marsh, 1875 Esthonychidae Cope, 1883 Kuanchuanius? danjiangensis sp. nov. Type A left M^1, GV86033. Locality and Horizon 100 m west of Zhanggou Village, Danjiangkou city, Hubei province; the lower part of Dacangfang Formation, middle Eocene. Diagnosis A middle-sized tillodont, M^1 paracone very closed to metacone, with a weak protoconule and enamel fold on trigon basin. Remarks The specimen collected from Loc. 86001, comparing with corresponding taxa of Paleocene and early Eocene forms known from Asia and North America, the conspicuous differences larger in size, more lophodont teeth, with enmal fold on trigon basin. Comparing with the middle Eocene tillodonts, K.? danjiangensis is basically similar to Trogosus of America, but it obviously differs from the latter in having a protoconule and a paracone cery closed to metacone on M^1. Tillodon being smaller size, Adipidium and Metaesthonyx with a mesostyle on M^1, they are quite different from Zhanggou form. Although the specimen M^1 is referred to Kuanchuanius (erected by Chow in 1963) in the paper, it cannot be directly compared with the material of K. shantunensis because none of the upper molars of K. shantunensis has been collected so far. Pantodonta Cope, 1873 Coryphodontidae Marsh, 1876 Asiocoryphodon progressivus sp. nov. Type A left mandible with P_2-M_3, GV86024. Referred specimens A right mandible with P_2-M_3, GV86025; a left maxilla with M^(2-3), GV85004; a upper premolar, GV85001; three upper molars, respectively GV86026, GV6027 and GV86029; the anterior part of a right mandible with I_3-C, GV86028; a right lower premolar, GV85003; a right M_1, GV85005; a lower canine, GV86085. Locality and Horizon 500 m east of Zhanggou Village, Danjiangkou city, Hubei province; the upper part of Yuhuangding Formation, middle Eocene. Diagnosis Middle size, pre- and post-protocristae of upper premolars weak, M^(2-3) hypocones directed to metacones, paracone of upper molar having a crista antero-posteriorly directed, M_3 with a weak crista hypoconulid. Remarks A new species, Asiocoryphodon progressivus, is in generic characteristics identical with those of genus Asiocoryphodon from the lower part of Yuhuangding Formation in this basin. By the diagnoses described above, however, the former can be easily told from the type species A. conicus. After having reexamined the material of coryphodontids from China, Lucas and Tong (1987) referred some specimens of Asiocoryphodon and all the specimens of Manteodon from the lower part of Yuhuangding Formation to a new genus Heterocoryphodon. Based on Lucas' description, in Haterocoryphodon M_3 without hypoconulid, M^2 very much larger in size than M^1 or M^3, obviottsly different from those of A progressivus. Metacoryphodn only collected from the middle Eocene strata of China, its lower molar oblique crest and paralophid weak, M_3 without hypoconulid, not the same characteristics as those of A. progressivus either. Asiocoryphodon sp. Specimen A right M^3, GV86030. Locality and Horizon Same as above. Remarks The M^3 may be referred to the genus Asiocoryphodon, but it is different from any other species of A docoryphodon mainly in the tooth outline relatively oval, the hypocone lingually located at the middle between protocone and metacone. It should point out that the later character is close to that of Heterocoryphodon, but A. sp. lacks such a welldeveloped posterior cingulum as Heterocoryphodon. Dinocerata Marsh, 1873 Gobiatheriidae Flerow, 1952 Gobiatherium minutum sp. nov. Type A left juvenile mandible with DP_3-M_1, GV85011. Locality and Horizon Same as above. Diagnosis A small uintathere, M_1 with a very weak hypoconulid crest and without an entoconid crest, a crista running from metaconid to metastylid, paraconid distinct. Remarks Gobiatherium minutum, in morphology, for example, lower molar paraconid and metastylid distinct, both entoconid and hypoconulid forming a posterior cingulum and so on, is similar to G. mirificum of Nei Mongol, especially to those of the two juvenile mandibles (A. M. 26622 and IVPP V5710). The species of Zhanggou, however, having smaller size, DP_3-DP_4 with more distinct paralophid, M_1 paraconid and paralophid well-developed, differs from the form of Nei Mongol. G.? major (Qi, 1987) differs from G. minutum in having much larger size, DP_3 larger in size than DP_4. Perissodactyla Owen, 1848 Lophialetidae Radinsky, 1965 Lophialetes? primus sp. nov. A right mandible with M_3 and a talonid of M_2, GV86064. Referred specimen A talonid of M_3, GV85017. Locality and Horizon Same as above. Diagnosis M_3 quite narrow and elongate, hypoconulid very distinct and sharp cone, the main cones of M_3 distinct. Remarks The specimens from Zhanggou Village should be undoubtedly referred to Lophialetidae, but they differ from those of any other genera in Lophialetidae in the following three aspects: (a) M_3 quite narrow and elongate (L/W=2.46); (b) M_3 hypoconulid quite distinct and sharp cone; (c) paralophid well-developed. Owing to similarity of the speciment to Lophialetes in general pattern, they are temporarily referred to Lophialetes in this paper. L.? primus would be assigned to a new genus if materials are collected in quantity in the future. Yimengia sp. Specimen A left juvenile mandible with DP_3-M_2, GV85015. Locality and Horizon Same as above. Remarks The collection is referred to Yimengia by the following faetures: (a) M_(1-2) oblique crest well-developed and extending to the posterolingual base of protoconids; (b) M_(1-2) tragonids triangle in outline; (c) lower molar paralophids distinct and arched. But it is quite different from any other taxa of this genus in the cones of lower molars distinct, protolophids relatively weak. Wang (1988) considered that? Lophialetidae indet. (IVPP V5372, Xu, 1979) from the top part of Dacangfeng Formation should be referred to Yimengia, it is obviously more progressive than Yirnengia sp. in phylogeny. Rhinocerotidae Owen, 1845 Forstereooperia? sp. The left lower molar (GV86081) from 500m east of Zhanggou Village is of a typical rhinocerotoid pattern, but it is smaller only in size than those of any other species. Eomoropidae Viret, 1958 Eomoropus? zhanggouensis sp. nov. Type A left M_1, GV86083. Referred specimens A left M_2 or M_3 (the posterior part of talonid broken), GV 86084; a left juvenile mandible with heavily worn DP_3-DP_4, GV85018. Locality and Horizon Same as above. Remarks The materials are relatively fragmentary except the M_1 (GV86083) completely preserved. Although the specimens are fewer and incomplete, they are in morphology relatively special, and seem to be similar to either those of eomoropids or propalaeotheres. Therefore, the specimens are questionably assigned to Eomoropus in this paper. The reasons for which the specimens are referred to Eomoropus are as following: (a) the lower molar narrow and elongate; (b) well-developed metastylid;. (c) the talonid wider than the tragonid; (d) the paralophid massive; (e) external and internal cingula less developed. On the other hand, the characteristics of E.? zhanggouensis similar to Propalaeotherium are as following: (a) the lower molar relatively brachylophodont; (b) oblique crest low and extending to notch between metaconid and metastylid; (c) metastylid and hypoconulid well-developed. It must be pointed out that the second feature similar to Propalaeotherium is extremely important one differring from that of Eomoropus. Comparing with Grangeria and Litolophus, E.? zhanggouensis has smaller size and some primitive properties, for instance, the main cusps quite distinct, paralophid massive. Discussion Of the seven taxa from the fauna described in this paper, except Asiocoryphodon, are mainly members of the middle Eocene fauna. The Zhanggou fauna, in the association of the mammal assemblege, is obviously different from the other middle Eocene faunas of China. It is indicated by the presence of early Eocene survivals and more primitive features of the known middle Eocene ones. Asiocoryphodon was only known from the early Eocene of China. Whereas the Asiocoryphodon of the Zhanggou fauna is obviously more advanced than that of the early Eocene faunas. In the Arshanto and Xizhou faunas, Metacoryphodon replaces Asiocoryphodon. The Xizhou fauna, however, contains Heterocoryphodon. Heterocoryphodon ranged from early to middle Eocene, so it does not indicate that the Zhanggon fauna is later than the Xizhou fauna in age. Of Perissodactyla, Yimengia and Lophialetes are common genera in the Zhanggou and Xizhou faunas, but they are more primitive than those from the Arshanto. The others, such as, Forstercooperia? sp., Eomoropus? zhanggouensis, and together with Gobiatherium (Dinocerata) are also more primitive than those of the Arshanto fauna. It is noteworthy that Kuanchuanius? danjiangensis, found in the lower part of the Dacangfeng Formation, is similar to Trogosus of N. America, and also resembles Kuanchuanius shantunensis of the Xizhou fauna in morphology. It may, therefore, indicate that the Zhanggou fauna is not at least later than the Xizhou fauna in age.