The Frog in the Stone

by Brian Dunning
September 14, 2010

Today we're going to take a rock hammer, split open a nodule of stone, and be amazed as a perfectly preserved frog hops out from a cavity within. This same surprising phenomenon has been reported since the fifteenth century, as many as 210 separate incidents, by some reports. If you believe the stories, frogs and toads have the ability to survive impossibly long time periods sealed inside solid rock. Examples include a toad extracted from a block of stone by excavators in Hartlepool, England in 1865; a British soldier working in a quarry during WWII who found one inside a slab of rock retrieved from 20 feet underground; and some French workmen who split open a flintstone in 1851 and found a living toad inside a cavity that perfectly matched its body contours. But these are only a few; many, many similar stories are found throughout the literature. With so many stories describing nearly the exact same phenomenon, one has to conclude that there must be something to it. Do frogs indeed have this astonishing ability?

A difficulty encountered when investigating this is that the majority of such stories are second and third hand reports from the 18th and 19th centuries. This means we don't have anything to examine, much less test. What we have is usually a pulp news reporter's interpretation of a story he heard from someone. That doesn't make it wrong, but it does add a chain of elements of unreliability to each story, and it certainly leaves us empty handed if we want to verify any part of it. We can, however, take a look at the science that is known. Is it possible for an amphibian — or any other animal — to actually go completely dormant for what seems an impossibly long time, and emerge alive?

There are two types of dormancy into which some animals enter to survive extreme conditions: hibernation, which happens during a cold winter; and estivation, a way of surviving a hot, dry summer. Both techniques involve a slowing of the metabolism, where breathing and the heartbeat slow down. The purpose of dormancy is to minimize the consumption of resources. These resources include both the animal's internal fuel stores and oxygen from the surrounding environment.

The purpose of hibernation is to escape the need to burn too much fuel to stay alive during a cold spell when adequate food is not available. Many frogs hibernate underwater. They slow their metabolism enough that they can get the oxygen they need through their skin directly from the water itself. Some will cover themselves partially with mud, but not entirely, because they need exposure to the oxygenated water. Some can also hibernate on land, usually under leaves or other woodland debris where they're still exposed to oxygen. They'll usually continue moving about, though slowly. No matter how cold it gets, most species won't freeze solid because of high glucose levels that lowers their bodies' freezing points, like antifreeze in your car. If a pond freezes over completely and the oxygen in the water is depleted, a hibernating frog will die. How long they hibernate depends on the temperature and region, but about half a year is the maximum. Longer than that, the frog runs out of calories and starves to death.

During the hot summer, a few species of frogs and toads estivate, which is all about preserving the body's water. They start with large water reserves in their bladder, then burrow down into the soil where it's cooler and more humid. Some species shed their outer layers of skin. These layers become a sort of watertight cocoon that seals the animal's hydration inside, all except for its nostrils which it needs to breathe. When the rains return, the animal breaks out of its cocoon and returns to the surface. Since estivating frogs and toads keep their nostrils open, oxygen is not a problem, and they can remain in this state as long as their calories and water hold out. Their metabolism drops to about 20-30% of normal. Estivation can last a maximum of about 10 months before stores run out, with the animal losing 50% of its total body mass.

Hibernation and estivation are the two known states into which frogs and toads can go to minimize their energy expenditure for extended periods. But if we want to explain the anecdotes telling of these animals emerging alive after decades, centuries, or even millennia of entombment in rock, we have to look elsewhere. Is it possible for a frog or toad to be completely hermetically sealed and preserved alive? There would be no water loss because there's nowhere for the water to go; but there's also no oxygen. Can the animal shut off completely, and remain alive?

In both hibernation and estivation, lipids are the primary fuel source, with fatty acid oxidation being the primary use of the energy budget. Proteins from muscle tissue break down into the amino acid glutamate which is also oxidized as a secondary fuel source. Along with a few other less significant energy sources, these chemical reactions keep the organs alive during the torpid period, but they're also needed to fuel the animal's arousal when it wakes up. The "frogs in stones" story requires these processes to stop completely, and to burn zero resources indefinitely, and then restart once the animal is exposed to oxygen as the rock is broken open.

Here's the problem with that. If all metabolic activity goes to zero, that's basically the definition of death, and the body is then chemically and biologically indistinguishable from a corpse. The various components of the immune system would stop as well. With zero metabolism, cells enter autolysis, in which the cell's own enzymes break down the cell tissue itself. Soon the only activity that would remain would be bacteriological. Like all animals, amphibians have bacteria throughout their systems. Bacteria serve crucial functions such as fighting infections and aiding in digestion. When an animal dies, one of the first things that happens is that the anaerobic bacteria, which do not require oxygen, break down the body's tissues. In the hermetically sealed environment, the bacteria would eventually die as well, but only after consuming all available resources; in this case, the body of the frog. To put it succinctly, if your metabolism stops, you will decompose, and you cannot live through it.

But let's give the benefit of the doubt to the frog, and assume there is some way — as yet unknown to science — that frog biology can avoid both autolysis and bacterial destruction when all metabolism has ceased. Let's even take a biologically implausible leap and grant that they've stayed hydrated and oxygenated, and have not consumed their stores of lipids and proteins. The stories tell of the frogs reanimating, even springing out of their stone tombs and hopping around. This energy exertion requires metabolism, and it requires that the muscles be biochemically ready for action. The only way this can be is if oxidation had been taking place for some time. In other words, the frog would have required substantial advance notification that he was about to be released from the rock, and his metabolism would have had to have found some way to jump start itself. It's hard to trigger something when you're biologically dead and have zero energy with which to do it.

My opinion is that the stories of frogs and toads entombed within solid rock are false, at least the way they've been reported. Some are known hoaxes, notably one example taken on tour by Charles Dawson (who also brought us the Piltdown Man hoax) and pictured all over the Internet in credulous articles. Fabrications aside, there are probably other explanations for what the witnesses perceived. Perhaps the material in which the animal was found was laid very recently, during the current construction project. Maybe it was not a hole but the end of a tunnel, the rest of which was destroyed by the excavation. Perhaps the frog came from elsewhere, and given the simultaneous timing of the witness splitting open the rock and noticing the frog, the witness erroneously concluded the frog must have come from the rock. We can speculate all day long, but there's minimal value in doing so. The fact is that all such stories — those that were not fabrications — were in different circumstances and probably had different explanations. I strongly doubt that a single phenomenon was the cause of every story, and my doubt is even stronger that the least plausible possibility is the one that actually happened.

The value of anecdotal stories like these is not as evidence, but to suggest directions for future research. If frogs could be proven to have this ability, it would overturn much of what we've learned, and would be a tremendous discovery for a biologist. If one is cold-hearted enough to experiment, it should be a simple matter to encase various species of frogs and toads into various types of stone-like materials, expose them to various conditions, and then crack them open in two years, five years, twenty years. Comparative tissue testing could establish whether they were able to get their metabolisms to stop completely, and then restart. If this proves to be the case, I will enthusiastically change my opinion.

And it turns out that at least one researcher has done just that. In 1825, the Rev. Dr. William Buckland, the English paleontologist who first described a fossilized dinosaur, buried 24 toads, each in its own block of either sandstone or limestone, each sealed with a glass window. He checked them one year later. All those buried in sandstone were dead and decomposed, while a few of those entombed in the oxygen-permeable limestone had successfully estivated and were still alive, though badly emaciated. He reburied the survivors for another year, and found them all dead. That sounds about like what we'd expect, given our knowledge of estivation. Stories tell of similar experiments done by others including the English naturalist Edward Jesse, often with better results, and all with (unfortunately) dubious credibility. Experimentation has — so far — failed to replicate what people think is happening, suggesting that the explanation for these stories may lie outside of the actual entombment of living frogs.

It's often been pointed out that astronomers, who spend more time looking at the sky than the average person, also report far fewer UFOs, because they actually know what they're looking at. We see a similar effect with entombed frogs. In all of the many reports, not one comes from a trained paleontologist or field geologist, who spend far more time carefully chipping away at rocks and paying close attention to what they're doing. That doesn't prove anything, but it does remind us that when a story comes from everyone except the experts, you generally have very good reason to be skeptical.

By Brian Dunning
Follow @BrianDunning