INVESTIGADORES
PUEBLA Gabriela Griselda
congresos y reuniones científicas
Título:
THE GNETALES (GYMNOSPERMOPHYTA) IN THE FOSSIL RECORD OF THE CRETACEOUS SAN LUIS BASIN, ARGENTINA: SYSTEMATIC ASPECTS
Autor/es:
MARÍA A. GOMEZ; GABRIELA GRISELDA PUEBLA; MERCEDES B. PRÁMPARO; ARI IGLESIAS
Lugar:
Mendoza
Reunión:
Congreso; 4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014
Institución organizadora:
IPA and CONICET
Resumen:
The Gnetales currently include three genera of seeds plants: Ephedra, Gnetum and Welwitschia, with
an evolutionary history still poorly known. Extant species are considered a remnant of a wider
biodiversity due to their divergent morphology and wide ecological range of life forms, and by
the palaeontological record (diverse and abundant polyplicate pollen grains). The phylogenetic
relationships between Gnetales and other spermatophytes have been debated as an important
evolutionary problem until recently. The present debate includes several different phylogenetic
hypotheses, alternatively relating them to different groups of gymnosperms or basal angiosperms,
which has led to a growing interest in their study. In the La Cantera Formation (Late Aptian),
San Luis Basin, central-western Argentina, a palynological assemblage, including abundant pollen
grains, as well as macroremains assigned to this group, were recovered. Polyplicate pollen grains
constitute more than 40% of the total of palynomorphs recorded in some levels of the type section
and are associated also with well-preserved macroremains. Among the pollen grains there are
morphological varieties with over 20 different morphological types assigned to different fossil
genera with gnetalean affinity: Ephedripites, Steevesipollenites, Gnetaceaepollenites. Pollen grains are
elliptical, inaperturate and polyplicate with a wide range of variation in pollen size and twisted spiral
or longitudinal plicae (similar to Ephedra). Some polyplicate grains show a longitudinal aperture,
similar to Welwitschia pollen grains. The macroremains include leaves, stems, cones and seeds, and
are comparable to Ephedra. Striated stems and branches with whorled leaves have been identified
among the studied material. Specimens with two leaf types were recognized: one type with two
linear leaves in opposite arrangement and the second type represented by scale-like leaves, with
threemerous whorled arrangement, with fused bases and triangular apex. Female cones are ovate
in shape, with thin bracts in three whorls: three to five small bracts at the first whorl, three broad
bracts at the second whorl, and three larger bracts at the third whorl were preserved. The margins of
bracts have lateral flanks extension (wings). Two ovoid seeds per cone with outer papillate envelope
were distinguished. Some specimens have a good preservation and exhibit cuticles and organic
remains that have enabled us to visualize in detailed anatomical features typical of these structures.
A detailed study on these fossils will provide new relevant information to the understanding of
homologies in reproductive structures of the Gnetales and its relationship with gymnosperms and
angiosperms.