Plant fossils are found in the well known Jurassic sedimentary basin in the Puttalum district, Northwestern Province, Sri Lanka. Fossil specimens were collected at a Tabbowa basin and the morphological characters of leaves, shoots and stems, were studied. Specimens could be diagnosed as conifers belonging to two genera Brachyphyllum and Pagiophyllum. The two genera closely resemble one another in foliar morphology. However, combined transmitted light and polarizing microscopic observations together revealed additional characters such as the pattern of leaf arrangement, cushions and keel size, shape of leaf apices and bases. Since cuticular are not preserved, specimens are assigned to their genus level only.
Both specimens have leafy axes with imbricate, spirally arranged scale like leaves. This indicates their affinity to family Araucariaceae (Araucaria) or Cheirolepidiaceae. On the basis of systematic affinity the specimens could be linked to the extinct conifer family; Cheirolepidiaceae, one of the dominant plant group during the early- mid Jurassic in the Gondwana land mass. Brachyphyllum serves as a thermophilic index plant species as a “climate indicator plant” of arid Palaeo-environments which prevailed in early Jurassic period. Thus the collected fossils confirm dry arid conditions in the mid Jurassic of Sri Lanka.
Key words: Conifer, Brachyphyllum, Thermorphilic, Palaeo-environment
Introduction :
Tabbowa Jurassic sedimentary deposit is a terrestrial deposit in a faulted basin rich in plant macrofossils compared to other two known Jurassic localities in Sri Lanka. This environment bears a rich and divers floral assemblage consisting of ferns, seed ferns, cycads and conifers. Among these Sitholey (1942) describe ...
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...e Tabbowa flora are small scale- to needle-leafed forms that is expected to characterise a relatively dry climate. The presence of cheirolepidiacean plants Brachyphyllum and Pagiophyllum favours dry conditions and Brachyphylum served as climate indicator plant of Early Jurassic period. Therefore, Tabbowa plant group may represent warm and dry climate in the mid Jurassic period.
References :
Harris, T.M., 1979. The Yorkshire Jurassic Flora, V. Coniferales. British Museum (Nat. Hist.), London, 166 pp.
Vakhrameev,V.A. 1987. Climates and the distribution of some Gymnosperms in asia during the Jurassic and Cretaceous; Review of Palaeobotany and Palynology,51:205-212pp
Vakhrameev, V.A., 1970. Range and palaeoecology of Mesozoic conifers, the Cheirolepidiaceae. Palaeontol. Zh. (1): 19-34.
Works Cited
conifer, Brachyphyllum, Thermophylic, Palaeoenvironment
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