Acta Geologica 35. (1992)

1. szám - Gy. Less: Numeric description of the equatorial section of the embryo with two chambers of orbitoid large foraminifers

Acta Geologica Hungarica, Vol. 35/1, pp. 3-26 (1992) Numeric description of the equatorial section of the embryo with two chambers of orbitoid large foraminifers György Less Hungarian Geological Survey, Budapest The possibilities of numeric description of the megaspheric embryo with two chambers being of primordial significance in stratigraphic evaluation of orbitoid large foraminifers are discussed. The development of the embryo is characterized by a new Z parameter changing between 0 and 100, in addition to the size of the two chambers. Besides the parameters representing the evolution within each evolutionary series, a new S parameter is also introduced, which proved to be relatively constant throughout the evolution; thus an evolutionary series can be distinguished. The joint use of the parameters Z and S renders unnecessary the description of embryo types by names, i.e. it eliminates the subjectivity caused by this on the one hand, and as against the parameters used so far, it allows the numeric characterization of any types of embryo without requiring new measurements. The possibilities of application are demonstrated by the European Lepidocyclinidae. Key words: Foraminiferida, Discocyclinidae, Asterocyclinidae, Lepidocyclinidae, Paleogene, biometry Introduction The significance of the size and quality of the А-generation embryo of large foraminifers is relatively well-known in the determination of taxa (Tan Sin Hok 1936; van der Weijden 1940; van der Vlerk 1959; Neumann 1958; Blondeau 1972; de Mulder 1975; van Wessem 1978; Schaub 1981; Fermont 1982; Setiawan 1983; Less 1987). The determination of the size and quality of the embryo has a double aim: on the one hand the distinction between the different but parallel evolutionary lineages, and the demonstration of the development of the given taxon within the evolutionary lineage on the other. The primary stratigraphic importance of the latter is well-known, mostly in the case of Lepidocyclinidae. There is no problem, in general, with the numeric characterization of the size of the embryo. On the contrary, the different embryo types are characterized both by names and numerically. Several kinds of numeric characterization have been developed. Nevertheless, the correlation of these and of the terms in use is for the most part occasional. In the following, an attempt is made to solve this problem. The suggested method is suitable to numerically characterize the equatorial section of the first two chambers of any foraminifera; the test, however, was carried out on Address: Gy. Less: H-1442, Budapest, Stefánia u. 14. P.O.Box 106, Hungary Received: 10 November, 1991. Akadémiai Kiadó, Budapest

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