A comprehensive re-assessment of the South African ovuliferous glossopterid
fructifications was conducted. This involved the creation of a database of
quantitative and descriptive information based on over 500 specimens from 14
localities in the northern and eastern Karoo Basin and the Bushveld Basin.
Specimens belonging to four families, thirteen genera and 24 species were
measured in detail, re-described, re-evaluated and in many cases, existing
diagnoses were emended. In total, this revision effected the creation of four new
genera, one new species and emendations to two families, seven genera and
thirteen species. All taxa were photographed, and representative specimens
were drawn and reconstructed. An illustrated key to the ovuliferous glossopterid
fructifications was compiled as a guide to the identification of all known species
from South Africa. The South African literature on glossopterid polysperms was
reviewed, with reference to discoveries from other parts of Gondwana.
All the glossopterid ovuliferous fructifications examined were impression fossils,
and a major component of the project was to re-evaluate the structure and
morphology of the specimens from a taphonomic perspective. Although not
widely taken into account in palaeobotanical studies, impression fossils are
essentially moulds of the original plant, providing valuable three-dimensional
information which is easily overlooked. This approach led to the discovery of
several radical, new morphological types in well-known taxa. These discoveries
could change the way glossopterid homologies are interpreted in the future.
Additionally, these structures may help to resolve some of the conflicting reports
regarding the presence of more than one set of cuticle per fructification, and
sterile scales.
Hirsutum intermittens was found to have a peculiar dual wing structure, and
was transferred to a new genus, Bifariala. In addition to the primary wing with its
tapered base, extended apex and apically inclined striations, an additional,
secondary wing was recognised in these fructifications, which has a structure
similar to that of Scutum and Gladiopomum. Hirsutum leslii was found to
possess a unique, hood-like wing which arched over the seed-bearing surface
iv
of the fructification, partially enclosing the ovules, which were in many cases
found still attached to the fructification. The species was deemed to be a junior
synonym of Elatra. The semi-enclosed structure of Elatra raised questions
regarding the pollination and seed dispersal mechanisms employed by
members of this genus.
A review of the literature on Arberia, and examination of South African
specimens, led to emendation of the genus to include the presence of a scalelike
extension distal to the single seed attachment point at ultimate branch
termini. Appreciation of the bifacial nature of some Arberia species, which bear
lateral branches across one surface of a laminate primary axis has important
implications for the recognition of homologies and establishment of evolutionary
trends among members of the glossopterids. Existing ideas regarding the
homologies and phylogeny of the glossopterids were refined and developed
further. The glossopterid polysperms are considered to have evolved from a
basal member of the Arberiaceae, with planation, fusion and reduction of lateral
branches having given rise to fructifications of the Rigbyaceae and
Dictyopteridiaceae. Members of the Lidgettoniaceae are thought to have been
derived from members of the Dictyopteridiaceae. The hypothesised derivation
of the glossopterid fertile structures from modified shoots rather than leaves,
supports an affiliation with the cordaitaleans rather than the pteridosperms.
The biostratigraphic and biogeographical significance and application of the
South African genera of glossopterid polysperms was briefly evaluated.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/5948 |
| Date | 19 January 2009 |
| Creators | Adendorff, Rosemary |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf |
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