How fossilization works like a lottery of fossilization —rare conditions preserve life, shaping our limited understanding of extinction and ancient history.
Numerous extinct animals are only recognized from bones, yet it is an often-overlooked fact that the odds are stacked squarely against the remains of an animal surviving at all. It has been projected that only one animal in billions will become a fossil. Therefore, of the billions of animals that have ever lived, only a minute fraction have left durable remains. The dinosaurs, although significantly older than the animals mentioned in this book, are a perfect example of just how rare fossilization is.
Also, the dinosaurs are a very well-studied group of fossil animals, yet in the 183 years since the first dinosaur was described, 330 species have been named. We’ll never know for sure how many species of dinosaur have walked the earth, but it must have been many, many times more than 330. The scarcity of fossilization is not surprising when you consider the fate of an animal after it has died.
If an animal dies in the wild, its carcass is rapidly dismembered; some bones may be cracked open, and what remains will be at the mercy of the elements. On the surface, they’ll be subjected to the slightly acidic bite of rainwater, the erosive power of the wind, and the ferocious rays of the sun.
Being underground may afford some protection, but acidic solutions percolate through the soil, and there are countless bacteria to digest the nutrients left in the bone. In the vast majority of cases, the bones of the long-dead animal are worn away to dust and nothing remains to show it once lived. Preservation also depends on where the animal lived.
If it was a denizen of warm, humid forests, the chances of preservation are even slimmer. Forests abound with hunting animals and bacteria, and if the bones manage to find their way into the ground, the acids produced by decomposing plant matter rapidly dissolve them away to nothing.
In the rare event of a bone surviving, or even more remotely, an entire skeleton surviving the rigors of scavengers, the elements, and bacteria, something rather unique must happen. The remains must be buried quickly after an animal dies, perhaps by a freak landslide or a fall of volcanic ash, in sticky asphalt, or in a bog.
With the remains well buried and protected, the process of fossilization can begin. Water percolating through the sediment or soil in which the bone lies carries silica and other materials into the pores in the bones, strengthening them and giving them the appearance of stone. Many of the animals in this book did not die long enough ago for their bones to have become completely mineralized, while others died in the wrong place for fossilization to occur. A textbook example of the latter are the remains that have been found in the dry caves of the Nullarbor Plain, Australia.
The animals that died in these natural pitfall traps never got buried, and their bones lay on the floor of the cave for tens of thousands of years before being seen by human eyes for the first time. The remains of these extinct Australian animals were still just bone, albeit very delicate, as no water had ever percolated through them to leave any strengthening minerals. Similarly, the remains of so-called Flores man, recovered from Ling Bua Cave in Indonesia, had not undergone any mineralization and were on the verge of decomposing altogether.
When we think of the remains of long-dead animals, we normally think of digging around in rock to find fragments of the living animal. Although this is often the case, animal remains are preserved in other ways, some of which are astounding. In some places in Siberia and Alaska, entire animals, such as mammoths, were frozen so quickly and later buried that they are almost perfectly preserved in flesh and bone, and today they provide us with the best glimpse we have of what these ice age animals were like. In very dry places, a dead animal can become mummified.
Some ground sloths have been preserved in this way, and even though the vast majority of their soft tissues have been eaten by insects and other small animals, fragments of skin and hair, thousands of years old, remain. Some animals met their end in peat bogs, and these deep beds of slowly disintegrating plant matter are excellent for preservation of animal bones and even soft tissues. Tar pits, like peat bogs, keep oxygen away from the remains of dead animals, and the bones that come to lie in these pools of ooze are unusually well preserved. The fossil record may be very fragmentary, but it is continually being added to.
Moreover, with every passing day, new fossils are revealed as the action of water, wind, and ice erodes the surface of the earth. Earth’s secrets are revealed to us slowly, and as scientists continually explore the far corners of our planet, searching for the remains of animals, they will add to our knowledge of what the earth was like and how it is changing.
With every passing year, new species are added to the list of animals that were. Who knows what amazing creatures will be found buried in sediment or frozen in permafrost in the future? The remains of some unknown animals will come to light only to be eroded away by the very forces that revealed them, and the only evidence of their existence will be lost forever.
The Lottery of Fossilization—The paleontologist Grayon E. Meade proudly poses with some of the numerous scimitar cat remains discovered in Freisenhahn Cave, Texas, during the summer of 1949. These cats’ remains were buried by sediment and the cave was sealed by natural processes. They lay undisturbed for thousands of years until paleontologists discovered them during excavations. Thus, the lottery of fossilization is a great knowledge to everyone.
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