Evidence for polymorphism of Palaeo flora from Jurassic beds in the Tabbowa Basin Sri Lanka

Sedimentary rocks of Jurassic age are found in few small, faulted, basins in the crystalline rock terrain of Sri Lanka, in the northwestern part of the country. Presence of plant fossils in some of the sedimentary rocks in those basins are well known and therefore, the present study was carried out mainly in one of these sedimentary basins; Tabbowa, focusing identification of the morphology of macrofossils in view of determining their systematic affinity to palaeo-environment. The observed characteristic features based on the characteristic venation distribution, pinnule margin and shapes of pinnules, were compared with those of local and international type specimens and with published literature, pertaining to various palaeo-climates. The fossil record of Cladophlebis sp. belonging to the family Osmundaceae are known as one of the oldest plant group since Permian period and as representing high diversity in the Early Jurassic. Detailed observations indicated that a many of the Cladophlebis spp. are assigned to different species belong to Jurassic: C. zeylanica Sitholey 1944, C. indica (Oldham & Morris) Sahni and Rao 1933, C. australis (Morris) Seward 1904 and C. antarctica Halle 1913 even in different countries. However, varying formats of description, varying terminology and the lack of systematic uniformity have often hampered identification of those species correctly. The present study and its identification of morphological and, (though limited) taxonomical features of the studied samples suggest that all species are closely related and possibly originated from one classic species, Cladophlebis denticulate Brongniart (1828) Fontaine 1889, known as a polymorphisms or intra-specific variability of its evolutionary process. In addition, this paper provides the morphological characters vis a vis taxonomic assignment and palaeoecological significance of the genus Cladophlebis.