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Credneria Zenker (Platanaceae): an extinct endemic plane tree from the Upper Cretaceous (Santonian) of Central Germany and its ancient environment
Stockholm University, Faculty of Science, Department of Botany.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Leaves of the Late Cretaceous angiosperm Credneria from its type locality in the Subhercynian Cretaceous Basin were investigated with morphological and statistical methods. Quantitative analysis of the morphological variability of the leaves suggests that the previously distinguished morphotypes Ia and Ib constitute sun and shade leaves of a single species, Credneria denticulata. Qualitative evaluation of the leaves reveals a combination of characters that link Credneria with the Platanaceae. Most determinative for this affiliation were an actinodromous venation, the presence of several pairs of suprabasal veins at the leaf base, spinose teeth and an inflated petiole base that originally enclosed the axillary bud. More than 50 species of Credneria have been described from localities outside the Subhercynian Cretaceous Basin. Although some of these species resemble the leaves from the type locality superficially, many of the determinative characters differ in detail or are absent. Many of these fossils were later assigned to Platanus. In the context of the pronounced provincialism of many taxa during the Cretaceous, it is likely that Credneria was endemic to Central Europe. Sedimentological features of the host deposit point to an accumulation of Credneria leaves in a tidal-influenced coastal landscape close to a shallow sea with cyclic transgressions and regressions. Credneria most likely inhabited a disturbed, early successional environment in a coastal delta floodplain. The occurrence of fossil tropical soils (hematitic oxisols) points to a warm and humid climate that probably was seasonal.

Keyword [en]
Credneria, Platanaceae, leaf morphology, morphological variability, quantitative analysis, character combination, sedimentary environment, Cretaceous plant ecology
National Category
Natural Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-62711OAI: oai:DiVA.org:su-62711DiVA: diva2:444090
Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2011-09-29Bibliographically approved
In thesis
1. Comparative morphological studies of fossil and living plane trees (Platanaceae) and oaks (Quercus): taxonomy, ecology, evolution
Open this publication in new window or tab >>Comparative morphological studies of fossil and living plane trees (Platanaceae) and oaks (Quercus): taxonomy, ecology, evolution
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Morphological characters are essential for flowering plant identification, but also provide information about diversity patterns and ecological adaptation. In woody plant species, characters of the leaf are among the most useful and can be examined on fossils as well. In this thesis, I studied leaf architecture, epidermal anatomy and reproductive structures of some fossil Platanaceae (plane trees) and an extant group of Quercus (oak) both qualitatively and quantitatively. The aim of this study was to understand past and present patterns of distribution in these taxa, their morphological variability and possible species delimitations. Platanaceae constitute today a relict taxon with a disjunct distribution, but were a taxonomically and morphologically diverse group in the geological past. The presence of the modern genus Platanus in the Late Cretaceous of Central Germany could be demonstrated through the combined analysis of leaves, flowers, fruits and pollen. The extinct genus Credneria is only represented by leaf fossils, but a unique combination of characters proved its affinity with the Platanaceae. Although several species had been described previously, a statistical analysis showed that the observed leaf polymorphism is due to environmental constraints, pointing towards a single species, Credneria denticulata. Quercus subsection Galliferae is a small group of white oaks with a disjunct distribution in the Mediterranean region, which show a high morphological variability within and low differentiation between the species. Samples from the entire distribution range were subjected to a morphological and quantitative analysis. The results demonstrated that the established species, except for Q. canariensis, are linked by clinal variation, which in turn corresponds to geographical gradients. An evaluation of epidermal characters revealed them to be of restricted use for taxon delimitation in the group. Instead, leaf and epidermal morphology provide extensive information about the ecology and biogeographic history of oaks.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2011. 53 p.
Keyword
Platanaceae, Platanus, Credneria, Quercus, Galliferae, leaf architecture, epidermal anatomy, comparative morphology, character variation, variability, sample size, diversity patterns, species concepts, ecology, biogeography, evolution, plant fossils
National Category
Botany
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-62707 (URN)978-91-7447-369-8 (ISBN)
Public defence
2011-10-28, Föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3. Manuscript. Paper 4. Manuscript. Available from: 2011-10-06 Created: 2011-09-27 Last updated: 2011-10-07Bibliographically approved

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