江西池江盆地阶齿兽一新种

<正>1962年在我国广东南雄盆地首次发现了阶齿兽类化石(周明镇等,1973;郑家坚等, 1973),随后在安徽潜山、湖南茶陵、陕西石门、江西大余等地的中古新世地层中相继发现该类动物的化石材料,尤其是在广东南雄、江西大余和湖南茶陵三个地点,有大量的阶齿兽类化石产出。阶齿兽类在中古新世时在亚洲南部是广泛分布的。本文记述的阶齿兽材料是2003年在江西池江盆地发掘到的,此标本与已知的阶齿兽属中各种均有明显差别, 故建立一新种——丁氏阶齿兽(Bemalambda dingae sp.nov.)。

NEW MATERIAL OF BAMALAMBDA FROM CHIJIANG BASIN IN JIANGXI, CHINA

Summary Bemalambda was first found from Nanxiong Basin, Guangdong Province in 1962(Chow et al. , 1973; Zheng et al. , 1973). The subsequent discoveries of bemalambdids from the Middle Paleocene of Qianshan of Anhui, Lingcha of Hunan, Shimen of Shaanxi, Chijiang of Jiangxi indicate that Bemalambda had a wide distribution in the Middle Paleocene of southern China. The specimen described in this paper was found from Chijiang, Jiangxi in 2003 and is distinctly different from those of other species in the genus. It represents a new species, Bemalambda dingae sp. nov. Pantodonta Cope, 1873 Bemalambdidae Chow et al. , 1973 Bemalambda Chow et al. , 1973 Bemalambda dingae sp. nov. (Fig. 1) Type A segment of lower jaw. The left il and canine are broken. The right lower jaw with p4 ~m3 is preserved (IVPP V 14394). Locality and horizon About 300 m southwest to Fengshuxia, Dayu County, Jiangxi Province; Middle Paleocene. Etymology Dedicated to Dr. Suyin Ding for collecting the specimen. Diagnosis The lower jaw is tumescent and thick, with its anterior part widened, the posterior margin of symphysis reaching the p2. The ramus mandibula are strong. The premolars are not molarized. The talon of p4 is not developed. The crown of m3 is square in shape and the talon of the tooth is not elongated. Comparison Bemalambda includes five species (B. crassa, B. nanhsiungensis, B. pachyoesteus, B. shizikouensis, and B. zhoui). The new species is probably the largest bemalambdid according to the width and length of the lower cheek teeth as shown in Table 1. The premolars of B. shizikouensis and B. nanhsiungensis have already molarized. The talon of the p4 of B. shizikouensis is well developed. The talon of the p4 of B. nanhsiungensis is a simple vertical ridge which extends posteriorly from the posterior margin of protolophid. However, the talon of the p4 of the new species is not developed and its premolar is not molarized. Although the premolar of B. zhoui is not molarized either, its lower jaw shows no tumescence. The lower jaw of the new species is tumescent and thick, the posterior margin of symphysis reaching the p2. The new species differs from B. pachyoesteus in that the latter is not widened in the anterior part of lower jaw. In addition, the two species are quite distinct from each other in molar morphology. The molar crown of the new species is square in shape, but the latter rectangular. B. crassa is represented by only upper teeth and is very similar to B. nanhsiungensis but relatively larger. Based on the features of the material from Chijiang, a new species is proposed - Bemalambda dingae sp. nov. Chow et al. (1977) regarded Bemalambdidae (Bemalambda and Hypsilolambda ) from the Paleocene of China as primitive pantodonts mainly according to the strongly V-shaped ecolophs on p3 ~ p4. Van Valen ( 1988) argued that they are non-pantodonts but palaeoryctoid derivatives. Muizon and Marshall ( 1992 ) suggested that the pantodont affinities of Bemalambdidae are featured by the possession of an incipiently V-shaped centrocrista and non-connate paracone and metacone. Therefore, the systematic position of Bemalambdidae remains uncertain.