| PALAEONTOLOGIA POLONICA VOL. 56 | ||
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Silurian Graptolite Faunas in the East European Platform: Stratigraphy and
Evolution |
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Teller, L. 1997. The subsurface Silurian in the East European Platform. In: A. Urbanek and L. Teller (eds), Silurian Graptolite Faunas in the East European Platform: Stratigraphy and Evolution. — Palaeontologia Polonica Abstract:
A state of art overview of the Silurian System within the deep substratum of the East European Platform
(EEP) is presented. Structural Regions are characterized in terms of
biostratigraphy, tectonics and palaeogeography. The most instructive sections based on keywells have been briefly described with an emphasis on the western margin of the platform. The Silurian basin displays a typical platform development and may be traced from the neritic to the deep basinal
facies. While the neritic belt is recognized from Gotland through Estonia, Volhynia to
Podolia, the deep basinal facies has been documented NE of the Törnquist Teisseyre
lineament. The results presented are based on some 700 deep borings. They offer a summary of Silurian history of NE Poland and the adjacent
areas, as well as a setting for graptolite biostratigraphy. |
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Abstract:
The sequence of graptolite faunas in the Wenlock and Ludlow Series in the East European Platform is
presented. The morphology of the graptolites discussed is based on the material isolated from the cores and from Baltic erratic
boulders. Main trends of morphological evolution have been recognized and
characterized. Along with the updating of the earlier record on biostratigraphy, new data including those on retiolitids are
provided. A modified zonal graptolite subdivision, comprising the Late Ludfordian is
presented. |
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Teller, L. 1997. Revision of certain Pridoli monograptids from the Che³m keysection (EEP). In: A. Urbanek and L. Teller (eds), Silurian Graptolite Faunas in the East European Platform: Stratigraphy and Evolution. — Palaeontologia Polonica Abstract: A review and revision of important graptolite index species for the Pridoli Series (Silurian) are given. P. rarus Teller, P. chelmiensis Teller, and P. samsonowiczi Teller are herein regarded as chronosubspecies of the single Istrograptus transgrediens (Perner) lineage, while some other taxa described in the 1964 paper proved to be merely astogenetic variants of the latter species. P. bugensius Teller and P. aduncus Teller are now considered junior synonyms of Colonograptus lochkovensis Pribyl. The latter species is assigned to a new genus, Neocolonograptus, erected in this volume by Urbanek. A revised scheme of the Pridoli zonal subdivision based on graptolites is presented. Key words: Graptolites, Silurian, Pridoli, biostratigraphy, taxonomy. Lech Teller, Instytut Paleobiologii PAN, ul. Twarda 51/55, 00 818 Warszawa, Poland. |
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Urbanek, A. 1997. Late Ludfordian and early Pridoli monograptids from the Polish Lowland. In: A. Urbanek and L. Teller (eds), Silurian Graptolite Faunas in the East European Platform: Stratigraphy and Evolution. — Palaeontologia Polonica 87-231. Abstract: Graptolites etched from the Mielnik 1 wellcore (E Poland) reveal the main features of the development of monograptid faunas within the late Ludfordian–early Pridoli interval. Fifteen species and subspecies are described and Monograptus (Slovinograptus) subgen. n. as well as Neocolonograptus gen. n. are erected. Morphology of many species has been described adequately for the first time and their systematic position corrected. Four graptolite zones of the late Ludfordian are distinguished. The late Ludfordian fauna, which appears after the kozlowskii Event, is composed mainly of immigrants dominated by hooded monograptids. They reappear as a result of the Lazarus effect. Some of them initiated the lobate spinose phyletic line terminating with Monograptus (Uncinatograptus) spineus, a highly characteristic index species. The lobate and the lobate spinose types are accompanied by bilobate forms (Pseudomonoclimacis latilobus). The graptolite sequence indicates that the appearance of the early Pridoli fauna was preceded by a biotic crisis, namely the spineus Event. Therefore this fauna is made up of a few holdovers and some new elements which developed from Pristiograptus dubius stem lineage (Neocolonograptus gen. n., Istrograptus Tsegelnjuk). This early assemblage, composed of bilobate forms, was later enriched by hooded monograptids, reappearing after the spineus Event. Both the late Ludfordian and early Pridoli assemblages abound in instances of homeomorphy and generic transitions. The latter occur due to independent acquisition by some forms of simple thecal characters which allows their assignement to a new genus. Another remarkable feature of Late Silurian monograptids is reduction in the number of sicular rings, and establishing of a steady relation between one of the rings and the virgella. This character state was independently achieved as a structural grade, by all, otherwise unrelated, phyletic lines of Late Silurian monograptids. Key words: Late Silurian, graptolites, monograptids, stratigraphy, taxonomy, biotic crises, oligophyly, homeomorphy, adaptive repetitions, anagenesis. Adam Urbanek, Instytut Paleobiologii PAN, ul. Twarda 51/53, 00 818 Warszawa, Poland. |
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Urbanek, A. 1997. The emergence and evolution of linograptids. In: A. Urbanek and L. Teller (eds), Silurian Graptolite Faunas in the East European Platform: Stratigraphy and Evolution. — Palaeontologica Polonica Abstract: Macroevolutionary effects due to anagenetic changes within a single lineage have been traced in the Linograptinae from Late Wenlock single stiped Lobograptus? sherrardae, through bipolar Neodiversograptus and multibrachiate Linograptus, to Early Devonian compound colonies of Abiesgraptus. The ability to generate a number of sicular cladia improved the stability of the rhabdosome, and, in the evolution of Linograptus, the resulting geometrical constraints were overcome by diverting their growth. The main lineage is subdivided into four chronospecies displaying periods of fairly high abundance and a distinct morphological norm. These periods were separated by intervals of comparative scarcity, probably related to the bottlenecking of the lineage. The only instance of change in large populations is the L. posthumusA. tenuiramosus phyletic transition. Speciation events (transformations) seem to be governed by the mechanisms of transient polymorphism, whilst periods of relative persistence of the norm were probably related to microevolutionary changes in monomorphic populations. A disparate origin of unit characters within the complex Abiesgraptus pattern is suggested. These characters appeared independently and heterochronously within the populations over the entire range of distribution of the ancestral species to be later assembled into a single adaptive syndrome. Cosmopolitan distribution of both the ancestral and the daughter species implies a polycentric or a pantopic emergence of the Abiesgraptus. Key words: Linograptinae, multiramous colonies, phyletic evolution, macroevolution, adaptive syndrome. Adam Urbanek, Instytut Paleobiologii PAN, ul. Twarda 51/55, 00 818 Warszawa, Poland |
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