Chapter-I Origins
Total Page：16
File Type：pdf, Size：1020Kb
CHAPTER-I ORIGINS 1 1. Why are snakes called reptiles? What is a reptile? Classification of animals is essential for their scientific study. Land-dwelling animal groups with backbone have been split into four classes: amphibians, reptiles, birds and mammals. Generally speaking, reptiles differ from amphibians by their dry, scaly skin; from birds by absence of feathers; and from mammals by absence of fur or hair. The class ‘reptiles’ consists of lizards, crocodiles, turtles and tortoises and snakes. There are about 6032 living species of reptiles, almost double the number of living species of mammals. 2. How many species of reptiles are there worldwide? Crocodiles : 22 Turtles and Tortoises : 242 Lizards : 2800 Snakes : 2968 -------- : 6032 -------- (The numbers are approximate). 3. How many species of reptiles are found in India? Crocodiles : 3 Turtles and Tortoises : 32 Lizards : 155 Snakes : 276 (It is not unlikely that a few more may be discovered). -------- : 466 -------- 4. How did snakes evolve? The evolution of snakes has been difficult to study because of the rarity of fossil evidence and the highly damaged condition of these fossils which are very fragile (See Q & A 10). Scientists, generally, believe that snakes evolved from lizards. But some scientists believe that snakes and lizards evolved independently of each other from a common ancestor. 5. Which is the nearest relative of snakes among lizards? According to current scientific opinion, the monitor lizards of the family varanidae are the nearest relatives of snakes. There are many species world-wide. Indian species: common Indian monitor (Varanus bengalensis), desert monitor (V. 2 griseus), yellow monitor (V. flavescens), water monitor (V. salvator). The tongue of the monitor is distinctive in that it is forked as in snakes. The monitor flickers its tongue just like a snake does to smell (See Q & A 32). The progressive stages in evolution from monitors to snakes are not known. 6. When did the first snake appear and where? A land-dwelling snake named Lapparentophis deferenni evolved most probably about 130 million years ago, during the early cretaceous period, in what is now north Africa. (The first humanoids, our ancestors, evolved less than six million years ago). 7. Which is the next oldest species known and from where? A marine species, Simoliophis, found in parts of Europe and north Africa that were once under the sea. This is believed to have evolved at the beginning of the late cretaceous period, 100 million years ago. 8. Which are the earliest known snakes still found? The two families to which Lapparentophis and Simoliophis (See Q & A 6 & 7) belonged became extinct by the end of the cretaceous period, 65 million years ago. Among the snakes that evolved soon thereafter, we still have with us the boas (family: Boidae) and the South American pipe snake (family : Aniliidae). 9. Which are the most primitive families of snakes that now survive? Aniliidae, South American pipe snake. Only a single species. Boidae: In this are included the boa constrictors, the sand boas and, till sometime back, the pythons. Pythons are now classified as another family, the Pythonidae. Another of the oldest groups of snakes consists of the families Typhlopidae, Leptotyphlopidae and Anomalephidae under which come the worm snakes. Interestingly, sizewise, the boas and pythons are at one end of the scale and the typhlops and their relatives at the other end. The longest snake in the world is a python; the smallest is a typhlop. See Q & A 101 & 102. 3 10. Why is there no dependable fossil record of snakes? The simplified and fragile body skeleton, the slender teeth and the delicate skull with many of its bones only loosely joined together have been responsible for a clear fossil not emerging. It has been said that the evolutionary tree of the extinct groups of snakes will never be reconstructed in detail. 11. What is the latest fossil evidence for snakes with legs? According to a 2006 report in Nature, a 90-million year old fossil snake has been discovered in the Patagonia region of Argentina. This is the most primitive snake fossil known so far. This snake had two legs. It has been named Najash rionegrina. Najash is Hebrew for ‘snake’; Rio Negro is the province of Argentina where the discovery was made. 12. How many families, genera and species of snakes are there worldwide? Taxonomy of snakes has been an uncertain field and there are frequent revisions in the classifications into families, genera and species. Snakes, hitherto unknown or undescribed, are also discovered and are described from time to time. An authoritative account is thus difficult to obtain. There is little possibility for any finality in the matter at any time. The following table has been prepared based on Chris Mattison’s The New Encyclopedia of Snakes, 2007. Even in this book, there are discrepancies between the figures in the tabular statement and in the narrative portions. The details in the narrative portions have been adopted in preparing the table below: Families : 20 Genera : 465 Species : 2968 Sl. Family Kind of snakes Distribution Genus Species No. 1 Anomalepidae Primitive blind Central America and snakes Northern and eastern 4 16 South America 2 Leptotyphlopidae Thread snakes Southern parts of North America, Central and South America, Africa, 2 95 Arabian Peninsula and Parts of Middle East 3 Typhlopidae Blind snakes Tropical andsubtropical 5 235 world Australia 4 Anomochilidae Dwarf pipe snakes Southeast Asia 1 2 5 Aniliidae South American South America 1 1 pipe snake 4 6 Cylindrophiidae Pipe snakes Sri Lanka / South East 1 10 Asia 7 Uropeltidae Shield tails South India and 8 47 Sri Lanka 8 Loxocemidae Mexican burrowing Mexico and adjacent snake parts of Central 1 1 America 9 Xenopeltidae Sun beam snake Nicobar Islands, South east Asia and 1 2 Southern China 10 Boidae Boas North, Central and South America 11 44 Madagascar and Asia, South eastern Europe 11 Pythonidae Pythons South East Asia 7 37 12 Bolyeriidae Round Island boas Round Island in the 2 2 Indian Ocean 13 Tropidophiidae Wood snakes or Central and South West Indian boas America and West 4 26 Indies 14 Acrochordidae Wart snakes India to N. Australia 1 3 15 Viperidae Vipers Most parts of the world 36 259 16 Atractaspididae Burrowing asps Africa and the Middle 11 68 East 17 Colubridae Non-venomous and Most parts of the world mildly venomous 309 1807 snakes 18 Elapidae Coral snakes, Most parts of the world cobras, kraits and 42 246 mambas 19 Hydrophidae Sea snakes Seas except the Atlantic 17 65 ocean 20 Xenophidiidae Old world except 1 2 Madagascar 13. How many families, genera and species of snakes are there in India? Families:11 Genera:82 Species:276 Sl. Family Kind of snakes Genus Species No. 1 Typhlopidae Worm snakes 3 18 Non-venomous 2 Leptotyphlopidae Worm snakes 1 1 Non-venomous 3 Uropeltidae Shield tails 7 34 Non-venomous 4 Xenopeltidae Burrower 1 1 Non-venomous 5 Pythonidae Large constrictors 1 2 Non-venomous 5 6 Boidae Small constrictors 2 3 Non-venomous 7 Acrochordidae Coastal / estuarine 1 1 Non-venomous 8 Colubridae The largest group worldwide and in India. Mostly non-venomous. 46 156 A few rear-fanged venomous. 9 Elapidae Similar to Colubridae in many respects, but front-fanged and 5 17 venomous. 10 Hydrophidae Sea snakes 7 20 Front fanged and venomous 11 Viperidae Vipers 8 23 Front fanged and venomous 14. Could the rattlesnakes of the Americas have evolved from the pit vipers of south and south-east Asia? Yes, in all probability. In the distant past, during the Ice Age, the Asian and the American continents were connected by an ice bridge which stretched from the eastern tip of Siberia to Alaska. Animals and plants had a passage from the Asian continent to the American continent through this land bridge (This accounted also for the earliest human arrivals in the Americas 30,000 years ago. Their descendents, the Inuit and Aleut peoples, still inhabit the remoter parts of Alaska). Many snake species including the boas and the pit vipers are believed to have taken this route from Asia to America. Some 10 million years ago, when the last Ice Age ended, the ice bridge disappeared and the waters took over. This stretch of ocean is now called the Bering Strait. (After Vitus Bering (1681-1741), Danish Russian navigator, who led the Russian expedition to determine whether Asia and N. America were at any time connected by land). The pit vipers from Asia which so migrated to the Americas are believed to have evolved into the rattlesnakes. Interestingly, the habit of vibrating the tail as the rattlesnakes do is found in many of the pit vipers of Asia though they do not have any rattles. E.g. The bamboo pit viper (Trimeresurus gramineus), the hump-nosed pit viper (Hypnale hypnale), the Himalayan pit viper (Gloydius himalayanus) – all found in India and elsewhere in South and South-east Asia. This habit must have marked the beginning of the evolution of the rattle. The habit of vibrating the tail is found in some species other than pit vipers also. Examples from India: Himalayan keelback (Rhabdophis himlayanus), cat 6 snakes (Boiga spp.), striped trinket snake (Orthriophis taeniurus), sunbeam snake (Xenopeltis unicolor). 15. What is special about the snake family colubridae? The largest family of living snakes, the colubridae, has 1807 species in 309 genera i.e. more than 60 % of the total snake species of the world. Its members have evolved to occupy every possible ecological niche. They are found on trees, on the ground, under the ground and in water. Though there are no sea snakes in the family, some members of the sub family Hamalopsinae are found in coastal and estuarine waters around South East Asia and certain races of Nerodia fasciata are found in the coastal and estuarine waters in the Gulf of Mexico.