摘要
Aucellina和Buchia是两个典型的外表形态趋同,但又分别是中Barremian—早Cenomanian和Oxfordian—Hauterivian期的双壳类分层化石。本文从足丝耳、足丝凹口和弹体窝形态,铰合区的韧带分布范围,假丝梳的存在与否,双壳不等程度,后耳和壳表放射脊和同心脊发育状况,及地质历程诸方面讨论了这两属的形态区别和时代差异。
Aucellina and Buchia play an extremely important role in the dating andcorrelation of Middle Barremian--Early Cenomanian and Oxfordian--Hauterivianrocks respectively. Nevertheless, these two genera share many common or similarfeatures though they are only distantly related and occurred at quite differenttimes. Sometimes they are so superficially similar that they could be easy tomisidentify. This is particularly the case in some Middle Barremian-Early AlbianAucellina, e. g., A. caucasica, A. aptiensis, A. jeletzkii, A. andiana, A. radiatostriataand some Late Jurassic Buchia, such as B. concentrica, B. lindstroemi, B. tenuistri-ata, B. mosquensis, B. rugosa and B. spitiensis. This has led to some incorrect exa-mples of dating. There are, however, really some fairly distinct differences between Aucellinaand Buchia at the generic level. Aucellina has pseudoctenolium but Buchia doesnot have any pseudoctenolium or ctenolium. The byssal ear of Aucellina is long,blade--like to shallow spoon--like with a very little deflection inward ventrally,never strongly folded, and barely protrudes over the commissural plane and hingemargin; the genus has a straight and flattened margin bearing ligament striae. InBuchia, however, the byssal ear is rounded, spoon--shaped to conical in outline; itinvariably tilts upwards and inwards the left valve and is out of alignment withthe commissure and hinge margin. The ligament, in Aucellina, extends to extremi-ties, it is interrupted by a tranverse ridge from the umbo and lies almost entirelyto the posterior of the beak on the hinge plate in Buchia. The resilifer of Aucel-lina is situated close to the centre of the hinge plate, triangular and opisthocline,more or less relatively deeply impressed. In Buchia, it shows an elongate triangu-lar form tapering posteriorly, bounded anteriorly by the transverse ridge, proso-cline and almost flat. Furthermore, in Aucellina, the Gelenkgrube is absent or occationally developedinto a shallow sulcus; it is deep, hoof--shaped, with nearly vertical walls in Buchia.In Aucellina, the right valve is always almost flat, but in Buchia, it is always moreor less convex. Aucellina often has large and distinct posterior ear which is oftenabsent or not so distinct in Buchia. Left anterior earis sometimes present in Aucel-lina but has never been preserved in Buchia. The umbo of Aucellina is usuallymore narrow and pointed than that of Buchia. Buchia has no pronounced radialribs except in the case of B. concentrica, but Aucellina does usually have. In Aucel- lina, the radial ornament often dominates the shingle--like concentric ornament,which is very closely and regularly spaced and sometimes tends to overlap theradial ornament. In Buchia, however, the concentric ornament is fairly strong anddominates the radial ornament which is more linear. In eastern Heilongjiang of Northeast China, there are abundant Middle Volgian-Lower Valanginian Buchia fossils in the Dong'anzhen Formation in Dong'AnTown, Raohe county, and many Aucellina fossils mainly of Middle Barremian--LateAptian age (probably extending into Early Albian)in the Upper Yunshan Forma-tion of the Longzhaogou Group in the Yunshan area of Hulin county and theLover Chengzihe Formation of the Jixi Group in the Ronghua--Pingyang area ofJidong county, Jixi Basin.
出处
《地质论评》
CAS
CSCD
北大核心
1992年第2期131-139,T001,共10页
Geological Review
基金
中国科学院南京地质古生物研究所所长基金
