摘要
本文着重描述了1980-1981年采自安徽和县龙潭洞的—类(鼠平)科化石.根据臼齿的特殊性状及其与相关属种的比较,建立了—新属新种——变异华南鼠(Huananomys variabilis).这种田鼠可能与水(鼠平)(Arvicola)有共同的起源,属早更新世——中更新世中晚期—绝灭的支系.
Some specimens of arvicolid rodents were collected from the Hexian hominid site but not recorded in the list of the original mammalian fauna (Zheng Shaohua, 1982, 1983) and Huang Wanbo et al., 1982) due to their particularity unknown at that time. The genus Hexianomys named by these specimens in the monograph about the mammalian fauna from the Hexian hominid site was first mentioned by Zheng and Li in 1990 and quoted by Repenning et al. at the same time and by Zheng and Han in 1991. The name Hexianomys, however, has become invalid with the delayed publication of the monograph. In order to avoid further confusion, I have to. use a new generic and species name Huananomys variabilis to replace the previous Hexianomys complicidens and offer independently it in this paper considering its important position in the Arvicolidae. The material of this new genus in the literature include those from not only the Hexian but also the Tianqiao locality of Guizhou. In this paper, the stress will be put on the description of the specimens from the Hexian hominid site. Family Arvicolidae Gray, 1821 Subfamily Arvicolinae Gray, 1821 Tribe Arvicolini Kretzoi, 1955 Genus Huananomys gen. nov. Type species H. variabilis sp. nov. Diagnosis Size medium. Cheek teeth rootless. Lower incisor passing from lingual to labial side of molars between the base of M_2 and M_3. Cement filling in the reentrant angles of molars developed. Enamel thicker on covex than on concave sides of salient angles. M^1, M^2 and M_2 normal as in Microtus. M^3 with four closed triangles behind the anterior loop. M_1 with three to five and M_3 with three closed triangles before the posterior loop, and M_3 without BSA_3. Derivation nominis Name the typical locality, Hexian, being situated in South China after the new genus. Huananomys variabilis sp. nov. Holotype One broken right mandible with I and M_(1_3) (IVPP, v6788). Referred material Two broken right maxilla with M_(1-12) respectively (v6788. 1-2); one broken left maxilla with M^1 (v6788.3); one broken right mandible with M _(1_3) (v6788.4); 21 M^1 (v6788.5-25); two M^2 (v6788.26-27); 6 M^3 (v6788.28-33); 27 M_1 (v6788.34-60); 13 M_2 (v6788.61-73). Diagnosis As for, the genus. Deriration nominis variabilis means the first lower molar with three to five closed triangles between the posterior loop and the anterior cap. Description M^1, M^2 and M_2 are essentially as in normal members of Microtus in patterns. All the lower and the upper molars are of rootless and filled with cement in the reentrant angles. The enamel is thicker on the convex than on the concave sides. M_1 consists of an anterior cap, five triangles and a posterior loop. There exists five salient and four reentrant angles on the lingual side and four salient and three reentrant angles on the buccal side. The lingual salient angles are obviously larger than the buccal ones. The salient angles are slightly blunt and rounded. The enamel is broken off on the anterior wall of the anterior cap and on both buccal and lingual salient angles of the posterior loop, sometime also on the ends of inner or outer triangles. The immature specimens (10.3% of the total) show the dentine space between triangles not tight closed and the anterior cap simple (fig. 3, L-N). In the mature specimens, the Is 1-4 are usually narrow, but the patterns of the anteroconid complex have great variation and can basically be assigned as the following three morphotypes: The first one has an elliptic AC with a small secondary fold on the buccal side, an wider Is 6 than Is 5, a BRA_3 as deep as the LRA_4, three to four closed triangles before the posterior loop (31% of be total) fig. 3, A-D). The second has a small and simple AC, a wide but shallow BRA_3 and three closed triangles when Is 5 widened or four ones when it narrowed (fig. 3, E-G) (17.3%). The third has a simple and semicircle AC, five closed or subclosed triangles before the posterior loop (41.4%) (fig. 3, H-K). The width of Is 5 and Is 6 are variable in different morphotypes. If regarding it less than 0.01 mm (near to the largest value of Is 4 as the closed, the number of specimens with closed Is 5(17) are satistically larger than those unclosed Is 5(12) and most of them occupy the range of 0.OO-O.05 mm, while the closed Is 6(7) are smaller than the unclosed (22) and in range of 0.15-O.20 mm (fig. 4). This seems clearly to indicate that the Is 5 is relatively narrower than the Is 6. M_3 has three triangles before the posterior loop. The dentine space between T_1 and T_2 is more confluent on the type specimen (fig. 2, a) than on the otherone. There is only two buccal salient angles due to disappearing of T_4 and a shallow BRA_2. As with M_2, the enamel is broken off on the anterior wall of tooth and both sides of the posterior loop M_3 is composed of an anterior loop and four alternate but almost closed triangles on the occlusal surface. There is three lingual and four buccal salient angles and two lingual and three buccal teentrant angles, of which, both BRA_3 and BSA_4 are very obscure. The buccal triangles are smaller than the lingual ones. The dentine space between T_2 and T_3, T_3 and T_4 are closed Measurements see table 1. Comparison The modern arvicolid rodents are animals adapted mainly to temperate and to arctic grasslands and are of Holarctic distribution. According to the present fossil records they have a long evolutionary history more than 5 M.Y. (Chaline, 1990; Repenning et al., 1990). With the rapid evolution, they have formed a complicated colony which is the most important object of study for zoologists and paleontologists. Thirty-one fossil and living genera listed and 121 species described by Martin A. C. Hinton (1926) laid a good foundation for us to understand arvicolid rodents. Recent years, the modern animals of this family have been classified into 17 genera and 111 species (Nowak and Paradiso, 1983) or 18 genera and 110 species (Corbet and Hill, 1980). From evolutionary point of view, however, paleontologists thought the living arvicolid rodents to have possibly as many as 25 genera (Repenning, 1987; Repenning et al., 1990). This disagreement bring about such a situation that no one result about number of genera of this family can be accepted by everyone. The increase of genera and species in number, however, seems an inexorable trend with improvement of study method and new discovery. Fossil Huananomys is a good instance in this respect. First of all, the new genus Huananomys differs from the living genera, Clethrionomys, Dinaromys (Dolomys), Phenacomys, Ondatra, Prometheomys, Ellobius and fossil genera, for example, Mimomys, Borsodia and Pliomys in the rootless of molars, and from those genera, Dicrostonyx, Lagurus, Prometheomys, Ellobius and Hyperacrius in the development of cement in the reentrant angles of molars, and from Synaptomys, Myopus and Lemmis in the position of the lower incisor shaft passing from lingual to buccal sides between the base of M_2 and M_3. The main difference between the genus Huananomys and those genera without the abovementioned three traits has been listed in table 2. All the characters of the new genus never concentrate completely on one known genus or sibgenus, though some of it are common with the other one, for example, the closed dentine space between T_1 and T_2 on M_3 can also be observed in these genera, Chionomys, Herpetomys and Orthriomys. Especially, the M_1 of Huananomys differs from those forms listed in this table in having three to five closed triangles. Discussion Up to now, the material of Huananomys have onlv been found from two localities,Hexian hominid site,Anhui and Tianqiao,Weining of Guizhou.The geologicai age of the Hexian site has been determined in different ways (Zheng, 1982, 1983; Wang 1986; Chen et al., 1987; Li and Mei, 1983). Though there exists various results among the different authors, it can be considered as the Zhoukoudianian (Zheng and Li, 1990; Zheng and Han, 1991). The Tianqiao fauna including Beremendia and some primitive rodents may be regarded as Nihewanian in age (s. s.) (Zheng and Li, 1990; Zheng and Han, 1991) and can be compared with European early Biharian or American Irving tonian I (Repenning et al., 1990). Many genera or subgenera with rootless cheek teeth, such as Allophaiomys, Ahicola,Dicrostonyx, Lasiopodomys, Microtus, Neodon and Pitymys began to occur in the world. This state probably indicate that the new genus iS of one of the relative primitive arvicolid rodents and in the evolutionary stage parallel to these genera or subgenera. If regarding the Tianqiao as the earliest and the Hexian as the latest, no obvious variation can be observed on the size of all the molars and on the patterns of occlusal surface of M^1, M^2, M^3, M_2 and M_3 except M_1 which seems to show some slight evolutionary trends: the age is older, the number of the closed triangles is larger and the secondary fold on the buccal side of AC is inclearer. However, three rather than five closed triangles are generally considered as the primitive trait. The M_1 with three closed triangles in the specimens of Huananomys is very similar to that of Arvicola in having a simple AC and an unrhomboid space between T_4 and T_5. Accordingly it can be inferred that the Huananomys has a common origin with the Arvicola which derived from Mimomys savinl. So it is better to put the Huananomys to Tribe Arvicolin rather than to Tribe Microtini. Zheng shaohua: Quaternary rodents of sichuan and Quizhou area (in press).
出处
《古脊椎动物学报》
CSCD
北大核心
1992年第2期146-161,共16页
Vertebrata Palasiatica
