Gastropods from the Permian of Guangxi and Yunnan Provinces, South China

Journal of Paleontology, Jan 2002 by Hua-Zhang, Pan, Erwin, Douglas H

ABSTRACT-Latest Permian gastropod faunas are relatively poorly known, limiting our understanding of the behavior of the group during the end-Permian mass extinction. Here we describe an assemblage of silicified microgastropods from the Heshan Formation of Guangxi Province, China, as well as some related Permian gastropods from elsewhere in south China. This is the youngest described Permian gastropod assemblage, and demonstrates that gastropod diversity remained high until the latest Changhsingian stage, immediately before the mass extinction. A total of 73 species are described, including one new family, nine new genera and 51 new species. The new family is the Plicatusidae. New genera are: Naticasinus, Zhonghuaspira, Microlampra, Propupaspira, Laxella, Plicatus, Luoguella, and Ninglangella. The new species are: Bellerophon (B.) yochelsoni, Retispira sinensis, Naticasinus sinus, Peruvispira jucunda, Manzanospira turrita, Porcellia paucituberculata, Microlampra heshanensis, M. orcula, Glyptospira pinna, Anomphalus fusuiensis, Straparella rotella, Holopea bacca, H.? teres, Aclisina multicarinata, Plaiyzona pulchella, P. nitella, P. luculenta, Goniasma fusuiensis, Straparollus minutus, Naticopsis (N.) shizishanensis, N. (N.) ninglangensis, N. (N.) heshanensis, N. (Jedria) quangxiensis, Trachydomia minuta, Trachyspira quangxiensis, T heshanensis, PloceoUga (Plocezyga) yunnanensis, P. (P.) varica, Pseudozygopleura micra, Micropt,chis channa, Palaeosti,lus fusuiensis, Soleniscus micidus, S. pactus, Leptoptygma laetus, Propupaspira eleganta, Girtyspira delicata, Ninglangella ninglangensis, Donaldina heshanensis, D. eleganta, D. quinquecarina, Streptacis regularis, S. fragilis, S. pravis, Laxella micra, Plicatus scalaris, P. multifilaris, Luoguispira micra, L. lineata, L. multilinea, Luoguella elegantula, and L. diana.

INTRODUCTION

THIS PAPER describes Permian age gastropod faunas from Heshan, Laibin County, and Fusui County, Guangxi Province and Ninglang, western Yunnan Province, South China (Fig. 1) which range in age from the Lower Permian (Chihsia) to the Upper Permian (Changhsingian Stage). This is one of the richest and most diverse set of assemblages yet described from South China. Description of these assemblages provides important new information on the distribution and persistence of gastropods during the Late Permian. Significantly, the occurrence of so many well-preserved protoconchs bridges a gap between the Carboniferous and Triassic and provides some of the first information on the protoconchs, and apparent larval ecology, for many late Paleozoic gastropod genera.

During fieldwork in Guangxi in 1985 and 1986, the senior author discovered several localities yielding silicified gastropods, and these comprise the bulk of the material described here. Specimens from Ninglang, western Yunnan were collected by the senior author during fieldwork with the Hena Duanshan Kaocha team in 1980. A few additional specimens from Hesan and Fusui Counties, Guangxi Province were sent to the senior author by Profs. Jin Yugan and Liao Zhuo-ting of the Nanjing Institute, who had acid etched several samples which produced numerous brachiopod and gastropod fossils. Silicification of specimens from these areas has allowed extensive collections to be assembled. Over 1,000 gastropod specimens were picked from the residues, some well-silicified, others only incompletely silicified. Most are very small (

PREVIOUS WORK

The earliest reports of Permian gastropods from South China were by Kayser (1883), Mansuy (1912) and Fresh (1911). More recently, ten papers have been published describing Permian gastropods from this area (Pan Y. T, 1978, 1983a, 1983b, 1983c, 1985: a total of 19 Lower Permian species and 10 upper Permian species; Yu et al., 1985: four Lower Permian and five Upper Permian species; Wang and Xi, 1980: 94 species in 51 genera; and Pan Y T and Yu, 1993: 47 species in 31 genera). Wang (1982) described 14 species in 12 genera from the Heshan Formation, Laibin County, Guangxi Province, and one species from the Chihsia Stage of the Lower Permian (Wang, 1985). Based on these collections, Permian gastropods are widely distributed through Zhejian, Jianxgxi, Hunan, Guangxi, Guizhou, Yunnan, and Sichuan provinces, with the maximum abundance and diversity in Guizhou and Guangxi provinces. Diversity appears to increase during the period, reaching a high during the Changhsingian Stage. Middle Permian gastropods are generally scarce, occurring as scattered individuals in limestone. During the earlier, Middle Permian (Maoukouan) interval gastropods are relatively abundant, with 13 species recorded from Yunnan and Sichuan provinces.

SIGNIFICANCE

Although the number of species described here is relatively few, this fauna has important implications for understanding gastropod extinction patterns during the Late Permian. Prior to the description of this fauna, the most well-understood faunas came from Pangea, particularly from west Texas, and they indicated a pattern of gradual disappearance during the Middle Permian, continuing into the Late Permian. Compilation studies provided no support for an abrupt decline at the close of the Permian (Erwin, 1990, 1993). These Chinese assemblages dramatically change this picture. As discussed in Erwin (1996), the taxa described here shift the final occurrences of many genera from the WordianCapitanian to the Late Changhsingian (see fig. 15.3 of Erwin, 1996). Consequently the extinction becomes concentrated in the final million years of the Permian, rather than being drawn out over perhaps 10-15 m.y. That such a limited number of specimens from one region could so dramatically change the apparent pattern of extinction is a cautionary note about the quality of the fossil record during this interval. A large number of protoconchs are described here, allowing inferences about the patterns of larval ecology. The influence of larval ecology on survival and recovery during the mass extinction will be considered elsewhere in conjunction with several other recently described Permo-Triassic faunas.