Prehistoric sharks escaped mass extinction 252 million years ago by 'seeking refuge in the depths of the ocean' A site in the South of France, has revealed small shark ancestor's teeth indicating that the fish swam into deeper oceans to survive 'great dying' One of the tiny T-shaped teeth typical of cladodontomorph shark species is less than a millimetre long and discovered in 135 million-year-old rocks Experts from the Natural History Museum in Geneva hypothesised the sharks moved to deeper oceans and lived there for a hundred million years Sharks have roamed the world's seas for more than 420 million years and now scientists think they know one of the secrets of their longevity. Experts believe they have solved the riddle of why sharks survived the mass extinction that began 252 million years ago, wiping out around 80 per of all life on Earth. Fossil evidence has hinted that the fish survived the global catastrophe, known as the 'great dying' by diving deeper. Early species of sharks were smaller and had unique teeth. Pictured, is an illustration of falcatid shark,which is one of the cladodontomorph shark species A paleontological dig site in the South of France, containing sediment from a younger Cretaceous ocean floor, has now revealed the teeth of a small shark ancestor, indicating that the fish swam into deeper oceans to seek refuge. One of the tiny T-shaped teeth typical of cladodontomorph sharks is less than a millimetre long and was discovered in 135 million-year-old rocks. Experts have hypothesised that the sharks fled the acidic coastal waters of the end-Permian period to move to deeper oceans and lived there for a hundred million years. The research, which was published in Nature Communications, is based on new evidence examining the anatomical study of the microscopic structure of animal tissues and morphological evidence - the structure of organisms. One of the tiny T-shaped teeth typical of cladodont sharks was less than a millimetre long and discovered in 135 million-year-old rocks Guillaume Guinot, a researcher at the Natural History Museum in Geneva, Switzerland, told NBC News: "It changes our view of how dramatic this extinction event was. 'The find suggests that there may be many more fishes living in deep ocean sediment deposits that haven't been found yet (and that may indicate that the) extinction wasn't that dramatic for cartilaginous fishes (such as sharks). The study reveals that the recorded gap in the cladodontomorph shark lineage represents the longest gap in the fossil record for an extinct marine vertebrate group. The report says: 'This discovery demonstrates that the deep-sea marine diversity, poorly known during most of the fish evolutionary history, contains essential data for a complete understanding of the long-term evolution of marine fish paleobiodiversity. The three species of cladodontomorph were relatives of modern sharks, rays and skates. The new findings suggest that modern sharks might have survived the great dying in a similar way - by moving to deeper areas in the ocean. However, Dr Guinot said there is no fossil evidence to prove that modern sharks swam to deeper waters.