We already know that the current fossil record is incredibly incomplete. The conditions needed to preserve the remains of an animal after it dies are so specific that only a fraction of the billions of creatures to have walked this planet will have been turned to stone. But with hundreds, if not thousands of species currently threatened with extinction today, how many of them will be preserved in the fossil record for future researchers to discover? The answer, depressingly, seems to be not very many, with most species likely to disappear without a trace, according to new research published in Ecology Letters.
Most fossils come from animals that lived in very specific environments. There are scant remains of animals that lived in rainforests millions of years ago, for example, because the conditions of these ecosystems mean that carcasses are quickly degraded by scavengers and bacteria, while the lack of sedimentation and acidic soil means anything that does remain is rapidly broken down. The vast majority of fossils we do have come from animals that lived in either dry environments, where they were buried quickly, or from watery habitats such as flood plains and wetlands, where the dead animals were covered in sediment.
This bias in preservation – let alone the bias of where people are actually able to hunt for fossils – has been known for a long time, but how does it apply to those species we’re currently losing in modern times? Some estimates suggest that species are going extinct at a rate around 100 times the natural speed, and that we are currently in the midst of a sixth mass extinction event (this one driven by humans). Will there be any evidence left behind of the thousands of species that we have pushed over the edge?
The odds, it seems, are not looking good. Researchers from the University of Illinois took the “Red List” of species, which is compiled by the International Union for the Conservation of Nature as a record of which animals are most at risk of extinction, and looked to see how many of these species were already represented in the fossil record. They found that of all the mammals considered to be at “high risk,” only 15 percent had left any trace to date. They also found that those most at risk are half as likely to leave any remains as those species with a low risk of extinction.
There are a few reasons for this, say the researchers. Size is an obvious factor, as larger animals are more likely to leave a trace, and so is geographical range. Many species that currently face extinction are small mammals living in restricted ranges, many in rainforests and mountains, and it seems unlikely that any of these will be preserved for future researchers to find. Unfortunately, this is just research looking at mammals, the picture for other groups, such as birds and reptiles, is even bleaker.
And even our extensive modern records of species might not be as permanent as we like to think. “As humanity has evolved, our methods of recording information have become ever more ephemeral,” says Roy Plotnick, who co-authored the study. “Clay tablets last longer than books. And who today can read an 8-inch floppy? If we put everything on electronic media, will those records exist in a million years? The fossils will.”