Movies such as Anaconda always spur interest in gigantic snakes. Sometimes reality surpasses the imagination of even Hollywood, and some of the Anacondas found in South America are actually larger than the anaconda in that movie.
Recently there was a picture of a supposedl 100-foot snake swimming in a lake in Borneo. Although it is pretty obvious that the pictures circulating on the internet are a hoax, it is pretty unlikely that even an unknown species could grow to such a size in Borneo, given the temperature conditions.
65 million years ago, just after the extinction of dinosaurs, large snakes were prominent. In Columbia, a fossil was uncovered of a snake with a length of about 45 to 50 feet with an estimated weight of 1.25 tons. The pits where these fossils were found are 1500 meters deep, due to the fact that it was used for mining coal and other minerals. The fossils are found in all depths, bur of course it has to be deep enough to get below the topsoil ad into the hard rock with the sediments deposited 65 million years ago.
The coal industry in Columbia is not a small business, so scientists are really happy when they are allowed to dig holes where coal is mined.
At the time the fossils would have been their living, breathing selves, North and South America were completely isolated. This isolation could be a reason why no large snakes have been found in the North American fossil record. Even today, the longest snakes found in North America are no larger than 25 or 30 feet.
The inland setup of the US could be another important factor to the lack of large snakes, due to the location being a less than stellar living environment for land-living snakes.
Large snakes have also been found in the fossil record other places than South America - e.g. 30 foot snakes are occasionally found in Africa. Theoretically, there could have been even larger snakes earlier on in warmer periods. However, as with fossils in Columbia, they are very difficult to find, as most tropical areas have been covered in forest for million of years - it is not many places there are rocks were fossils can actually be found.
For every foot you add to a snake of that length, it really becomes much more massive. In a period of abut 20 million years, those snakes were probably the longest land living animals, comparable to Tyrannosaurus Rex, which were no longer there. From its bone structure it is probably closer to boas than to pythons. Regarding its mode of living it was probably living like an Anaconda. That is, swimming and searching for food and also spending some of its time on land.
It was no problem for a snake of this size to stay buoyant and to swim. Like whales, there is no problem in swimming around, and when they are so long it really has an effect whenever they move their tail.
It wouldn't make sense to say that the snakes at that time were larger just because they perhaps had access to more and better food resources. However, it lived close to Equator which seems to have an impact on cold blooded animals. The closer you get to the poles the smaller they usually are.
To sustain a high metabolic rate, they have to have a high temperature and that is easiest when you are close to Equator. Therefore, all the larger snakes today also live in Tropical areas. Around 60 million years ago the average temperature was 30 to 34 degrees Celsius, which is 8-10 degrees warmer than it is today in tropical areas of the world.
That is also why stories such as the one with the 100 feet snake are unrealistic. This is the same with insects, the warmer it is the larger the animals. This only holds for animals breathing air, so it doesn't hold for fish.
Within the next 100-200 years the earth is likely to move into a temperature range like the one we had 65 million ago. Therefore one could think that we again would see very large snakes. Indeed a potential for larger snakes is possible. However, it will take a long time before species has adapted and evolutionized to beadapted to the new conditions with higher temperatures. Furthermore, habitat destruction is probably taking place much faster than the global warming, and therefore there is no reason to believe that we gigantic snakes will remerge in the near future.
Animals are already moving as a consequence of rising temperatures, but that is an initial response. We remain to see and understand the evolutionary response to increased temperatures - changes in body size in relation to physiology. It is likely that this response is much slower.
As late as 2009, a fossil snake was found that not only deserves the title of the world's biggest snake, but the biggest snake of all time! The snake, probably a non-venomous boa constrictor was found close to the Equator. Its size is estimated to have been approx. 43 feet (13 meters); its weight was estimated to 2300 pounds (1140 kg).
It is estimated that in order to sustain itself, this gigantic snake would have needed a temperature of about 90 degrees Fahrenheit which was also the temperature in Equator 60 million years ago.
The biggest snakes today are not 43 feet long, in fact they are much smaller. The biggest snake held in captivity is probably «fluffy». Although there may be bigger snakes out in the wild, this snake, a reticulated python, has a length of 24 feet.
In 2009, a 49 foot long snake was found in Indonesia weighing 984 pounds making this snake the currently longest living and world's largest snake.
The biggest venomous snake in the world is the King Cobra by they way. They can reach lengths of up to 20 feet