河南新安中中新世利齿猪一新种

本文记述了河南新安中中新世利齿猪一新种: Listriodon xinanensis sp. nov.,讨论了中国各种利齿猪的分类位置和新种的变异; M. Pickford 和 A. F. Wilkinson(1975)把印度不同大小的两种猪 Listriodon pentapotamiae 和 Listriodon theobaldi 看作是不同性别的同一种的观点,可能是不正确的.

A NEW SPECIES OF LISTRIODON MEYER (SUIDAE, ARTIODACTYLA, MAMMALIA) FROM XINAN, HENAN

The specimens of Listriodon described here were collected from Jianshan near the village Licun, about 45 km west of Xinan County, Henan Province in 1978. They include several skulls, mandibles and some isolated teeth. Judging from the morphological characters of these specimens, they may represent a new species of the genus Listriodon Meyer, i.e. Listriodon xinanensis. Order Artiodaetyla Owen, 1848 Family Suidae Gray, 1821 Subfamily Listriodontinae Simpson, 1945 Genus Listriodon H. v. Meyer, 1846 Listriodon xinanensis sp. nov. (Plate I-III) Type A fragmentary male skull (V8283) with incisors (left I~3 broken), right upper canine, left and right cheek teeth. Locality and Horizon Xinan, Henan; Tunggurian, Middle Miocene. Further material see the Chinese text Diagnosis A listriodont of medium size, slightly smaller than L. mongoliensis. Very elongated preorbital region and reduced postor bital one; nuchal crest overhanging the occiput and the foramen magnum; a large infraorbital foramen over P~2P~3; palate narrow. Dental formula: Pl absent; upper male canine long and robust, curved outwards and backwards, round in cross-section; upper female canine small and slightly incisorform; I~1 relatively high crowned in comparison with that in L. splendens; P~2 and P~3 with well developed but low lingual ridge besides high labial cusp; P_2 and P_3 possessing marked transverse talonid ridge; P~4 having tightly connected two external cusps; M~3 with a true talon formed by single lingual tubercle or by inflatted post-internal cinglum. Remarks So far, thirteen species of Listriodon Meyer have been recognized from the Orleanian to the Vallesian land mammal ages in the Old World. They are grouped in three types by virtue of their molar structure: bunodont, lophodont and an intermediate buno-lopho-dont form. Among them the European L. splendens Meyer and the Asian L. pentapotamiae Lydekker, L. theobaldi Lydekker, L. mongoliensis Colbert, L. lishanenis Li et Wu, and L. robustus Yan belong to the lophodont form of the genus Undoubtly, the Xinan suid described here is also to be assigned to this form because of its lophodont molars. It is quite close to the Chinese L. lishanensis and L. robustus. They have the following characters in common: absence of Pl; connected two external cusps of P~4; P_2 and P_3 possessing a high and inflatted main cusp, the tip of which directs backwards. However, the Xinan suid is larger in size and there are several features distingushing it from L. lishanensis: I~2 formed by a single compressed cusp, and triangular in labial view; more robust male upper canine, curved outwards and backwards, round in cross-section; much more nearly connected two external cusps in P~4; P_2 and P_3 with markedly developed transeverse talonid ridge; M~3 provided with a talon; relatively elongated preorbital region and narrow palate. It differs from L. robustus in M~3 having a true talon, P~4 possessing mach nearer connected two external cusps, premolars more lophodont and molars more robust. Moreover, the Xinan suid also differs from the another known Chinese species L. mongoliensis by P~4 possessing much near connected two external cusps and lacking cleft on its labial surface, and by the narrow palate. In comparison with the European L. splendcns and the Indian L. pentapotamiae and L. theobaldi, the Xinan suid can be discriminated by the following characters: large size, narrow palate, a large infraorbital foramen over p~2-P~3, male upper canine curved outwards and backwards, absence of P1, P~2 and P~3 having respectively a well lingual ridge, P_2 and P_3 respectivelv possessing a transeverse talonid ridge, I~1 relatively high crowned, etc. Therefore, it is reasonable to erect a new species of the genus Listriodon Meyer for the Xinan suid. The variations shown by the new species Listriodon xinanensis indicates either individual variation or sexual dimorphism. The former can be observed on the female skulls: in the width of the skulls and in the detailed structure of the teeth. For example, the skull (V 8285) is rather narrow at the palate and at the snout-frontal part in comparison with the other female ones (Table 1); the talon of M~3 on some skulls (V 8284, V 9286 and X 8288) is bigger and formed by a single lingual tubercle, but on the other skulls (V 8285, V 8287), it is small and is formed by an inflatted poste-internal cingulum; the posterior cingulum of M~2 is present at its base and links up with the posterior ridge of the hypocone on the skulls V 8284, V 8286 and V 8287, however, it stretches to the top of the hypocone on skulls V 8285 and V 8289; besides, the shape and size of the two external cusps of P~4 are also variable....etc. The sexual dimorphism is mainly shown in the shape and size of the upper canine. The male upper canine is large and robust, curved outwards and backwards, and has a wide enamel band on its ventral surface. In contrast, the female canine is small and slightly incisiform. In addition, the premolars of the male are wider, the skull and mandible are more robust, the frontal-nasal part is broader than those in the female, and the expansion of the upper male canine shelf, spreading outwards, makes its snout much wider... etc. Notwithstanding all these variations, the length of the preorbital region remains nearly equal in both the male and female skulls; the total length of the dentition, especially the length of P2-M3, varies only slightly (Table 1 and 2). Judging from this, it might be incorrect that M. Pickford and A. F. Wilkinson (1975) regarded L. pentapotamiae and L. theobaldi from Siwalik as sexual dimorphism of the same species, because of their size difference in teeth only. The lophodont Listriodon is now known from a number of localities in Europe, India and North China. They occur in deposits often considered to be equivalent to the Astaracian or Tunggurian land mammal age (the European and Chinese Listriodon) and the Vallesian stage (the Indian Listriodon). It is very interesting that in every locality in North China, such as Tung Gur (Nei Mongol), Lengshuigou (Shaanxi), Fangxian (Hubei), and Xinan (Henan), Pataeotragus and? Oioceros are often accompanied by Listriodon. Therefore, the group (Listriodon-Palaeotragus? Oioceros) might become one of the characteristic element of the Tunggurian fauna in North China. If this is reall yso, the Xinan assemblage along with the Lengshuigou assemblage should be considered identical in land mammal stage, i.e. Tuggurian. However, the latter is earlier in age than the former.