| 论薇角石科Lituitidae(头足类) |
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| ON LITUITIDAE (CEPHALOPODS) |
| Based on the literature and practical materials about Lituitidae, this paper deals with the distribution and phytogeny of Lituitidae and the diagnoses of genera in it. The fossil lituitids first appeared at the Late Arenig, distinctly developed at the late Llanvirn (the Late Guniutan stage), decreased its development at the Late Caradoc (the Pagodan stage) and completely disappeared before the Middle Ashgill (the Wufengian stage). Their flourishing periods are very long in China, being restricted within base limits in Sweden and middle limits in Norway.According to its siphuncular position, the morphological changes of the shell and the surface ornamentations, the family Lituitidae can be divided into three generic groups. The Lituites group, consisting of Lituites, Trilacino-ceras and Cyclolituites, has a early tarphyceraconic portion, long and slowly expanded orthoceraconic portion with centrodorsal siphuncle. Ancistroceras, Holmiceras and Angelinoceras are also closely related and are the constituents of the Ancistroceras group which has a neanic tarphyceraconic or gyrocera-conic portion, rather short and rapidly expanded ortlaoceraconic portion with a nearly central siphuncle. The Sinoceras group, consisting of Sinoceras, Yang-jiapingoceras, Rhynchorthoceras and Tyrioceras, is characterized by a early slightly curved cyrtoceraconic portion and rapidly expanded orthoceraconic portion with a essentially central siphuncle. The Lituites and Sinoceras groups stem from the Ancistroceras group in a short period. Ancistroceras is the stemming genus of Lituitidae. Up to now, the first undoubted representative of lituitids would be Ancistroceras shangligangense Qi of China.The genus Sinoceras which is divided into two groups in this paper, having a slightly curved neanic portion, its ornamentations being five sinus and five salients, should be included in the family Lituitidae. Based on new materials its diagnosis is emended as follows.Rapidly expanded, essentially straight cone with slightly curvature towards the dorsal side near apex.The ornamentations consisting of weakly annulations and growth lines near apex, only growth lines on remained portions of the conch, appearing five sinus and five salients in early neanic stage. In the Sinoceras chinense group, the abult growth lines forming three sinus and three salients, the gerontic peristome five sinus and five salients, while in the Sinoceras xinjiangense group, both of the adult growth lines and the gerontic peristome presenting four sinus and four salients. The cross section of the cone circular or slightly depressed, with a central or dorsal of central siphuncle. The septal necks, nearly one half or one fourth camera length, straight or weakly arc towards inside. The connecting rings thin and cylindrical with very rich cameral deposits.The Sinoceras chinense group is distributed in the Yangtze and Jiangnan regions, while the Sinoceras xinjiangense group occurs in the Tarim region or probably the North China and Tianshan-Hingan regions.The surface growth lines of Tyrioceras are very similar to those of Sinoceras xinjiangense sp. nov., The latter appear to be older than the former in the occurring horizon. It is assumed that the Tyrioceras is developed from the Sinoceras xinjiangense group.In this paper, three genera and seven species of lituitids are descrided, among which five species are new. |
| LAI Cai-gen.1986.ON LITUITIDAE (CEPHALOPODS)[J].Acta Geoscientica Sinica,8(1):107-126. |
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