Evolution of a slither - study tracks snake's loss of legs

Haifa researchers help discover that world's snake species indeed evolved - just as Genesis reports.

By JUDY SIEGEL-ITZKOVICH
snake bites 224.88 (photo credit: Piet Spaans)
snake bites 224.88
(photo credit: Piet Spaans)
The Book of Genesis reports that the serpent who persuaded Eve to tempt Adam was cursed by God with the loss of its limbs: "Upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life." Now 16 researchers from universities and research institutes in four countries - including Haifa's Technion-Israel Institute of Technology - have found that the world's snake species had indeed evolved from four-legged lizard-like creatures some 140 million years ago. Dr. Ram Reshef of the Technion's biology faculty worked with scientists from Leiden University in the Netherlands, Whitman College in the US and the University of South Australia on a study entitled the "Evolutionary origin and development of snake fangs" which recently appeared in the journal Nature. In the extremely technical submission, the scientists show how the front legs gradually disappeared, followed by the disappearance of the hind legs, forcing the creature to slither on its belly. In some snake species, an undeveloped thigh bone can still be found. The disappearance of the limbs caused the snakes' bodies to sprout fangs and glands, some of which produce toxic venom, to protect the animal and improve its hunting abilities. Reshef and his colleagues noted that as snakes evolved into limbless creatures, their bodies lengthened and they gained access to subterranean "niches" of sustenance not utilized by other animals. But the loss of their limbs made it very difficult for snakes to catch prey and hold it in their mouths. The researchers (who do not mention the Bible's account of the serpent in the Garden of Eden) said their studies indicated that snakes had undergone a large number of "dramatic" evolutionary changes. A relatively large number of skull bones had detached themselves from the bones covering the brain, making the mouth much more flexible. The release of a bone connecting the skull bones and the lower jawbones had allowed the jaws to open much wider and the snakes to swallow whole a variety of larger prey - sometimes animals bigger than the snakes themselves. The more advanced snake species are able to kill their prey by squeezing them with their massive trunk muscles. As the species evolved, some developed a special gland in the back part of the upper jaw that produced venom to ease the process of capturing and consuming their victims. The Nature article ends a long debate by scientists on the source of fangs in advanced species such as rattlesnakes, pythons and cobras. Reshef contributed to this understanding his discoveries on the embryonic development of snake species native to this region and the SHH gene, which expresses itself in the development of fangs. He discovered that the fangs in snakes with poisonous venom originate in the back part of the maxillary teeth. Although they originally were of equal size, about 60 million years ago they broke into two regions, with some turning into large fangs. The venom, consisting of enzymes and toxins, flows through the fangs when the snake bites.