The island Sri Lanka is situated in the Indian Ocean, south west of the Indian peninsula, between longitudes 79o 39’ and 81o 53’ E and latitudes 5o 54’ and 9o 52’ N, and has a total land area of 65,600 km2. The island is about 60 km from the southwestern tip of the India. And it contains a variety of habitats, from the hot, dry plains of the north, east and south, to the central mountains that ascend 2,524 m above mean sea level (Piduruthalagala). Major rivers in the island include Mahaweli River (335 km). The coast of Sri Lanka is fringed with sandbars and lagoons.
As has been noted by Cooray, 1967; Das, 1996 and Somasekaran, 1988, Sri Lanka bears many geological similarities with parts of the Indian peninsula. A land connection between the northern tip of Sri Lanka and the southern tip of Indian peninsula has existed from time to time in the past. Responding to the highly diverse ecological conditions and as a result of past history, the biota of Sri Lanka includes a fascinating admixture of elements that are Indian, Indo-Malayan, African, Eurasian and also includes a large portion of elements that may be described as indigenous or endemic to the island. Sri Lanka is one of the global hotspots for high biological diversity.
Most of land area of Sri Lanka divides in to two distinct climatic regimes; wet zone and dry zone. Rainfall is seasonal and related to periods of characteristic monsoon winds. The southwest monsoon (May to September) results in rainfall mainly in the wet zone, whereas the northeast monsoon (November to February) causes rainfall in all pars of the island (Cooray, 1948).
Vegetations reflect the combined effect of topography, climate and soils. In Sri Lanka the natural vegetation is predominated by diversity of forest types. The most extensive type of forest in the island is the dry mixed evergreen forest found in dry zone. In the intermediate zone, the vegetation gradually changes in to moist semi-evergreen forests. In the wet zone vegetation has been largely categorized by elevation with wet-evergreen forests in the lowlands and hills, lower montane forests on the lower slopes of the mountains (Ashton et al, 1997; Gunathilake & Gunathilake, 1990).
Class - Reptilia, AN INTRODUCTION TO REPTILES
|Classification of Class Reptilia
Cotylosauria- stems reptiles (extinct)
Chelonia (Testudine) - Turtles, Tortoises, & Terrapins
Sauria (Lacertilia) - Lizards
Serpentes (Ophidia) - Snakes
Amphisbaenia- worm lizards
Saurischia- lizard pelvis “terrible lizard “Dinosaurs (extinct)
Ornithischia- bird pelvis “second main group of Dinosaurs (extinct)
Class Reptilia is also known as dry skinned poikilotherms. They are ectothermic vertebrates belonging to kingdom Animalia, phylum Chordata, subphylum Vertebrata (Craniata).
Most early reptiles are extinct & only fossils remain. Our studies are presently based on these remaining fossil forms.
The basic classification of presently ruling reptilian have four major groups is based on anatomy of the temporal region of the skull & the number of openings. These are;
Occurrence of reptiles was taken place on earth in Carboniferous period 280-345 million years ago. It’s believed that the early reptiles arose from labyrinthodont amphibian stock. There special adaptations allowed them to inhibit a tremendous range of habitats & to dominate Mesozoic era with most spectacular radiation, which was later named as “the age of reptiles”. The size of early reptiles rarely exceeded 10 feet. They had short legs, & heavy bodies. Also they were slow moving animals.
Reptiles are the first tetrapods that adapted to live basically on land. Reptiles comprise the majority of tetrapods alive today which have shelled eggs & embryonic membranes. Formation of foetal membranes in the embryo such as amnion, chorion, & allantois in reptiles is a remarkable feature in development of them & also it’s considered as a characteristic feature of higher vertebrates, who are grouped together as Amniotes.
Reptiles evolved as the first group of terrestrial vertebrates. It’s believed that the birds having an ariel habitat & mammals adapting to land were evolved by reptiles. Even though birds & mammals are warm blooded, reptiles are cold blooded. Due to this feature, their distribution & activities are limited which has become a disadvantage on survival. But they show a better success features in surviving in dry terrestrial environment, when compared with the Amphibians.
As a group, reptiles have been quite successful land dwellers & underwent a high radiation, by invading the land, water & even the air during Mesozoic era. But today no aerial reptiles are found. Reptiles occur in wide variety of habitats. In tropics they can be active at all seasons, but in temperate their only active in warmer months. In deserts or semi deserts they are active on warm days in spring & autumn, but in summer many species avoid excessive midday heat.
Today only four widely divergent orders are alive. These are:
- Squamata; Saurians, Serpentes, & Amphisbaenians
- Rhynchocephalia; Lizards like Tuatara
- Chelonia; Turtles & Tortoises
- Crocodylia; Crocodiles