Tomorrow’s fossils will represent fewer species, more humans

By Zack Fishman
Medill Reports

The piping plover, an endangered shore bird that spends summers on the Great Lakes and the Atlantic coast, is recovering as a species. After more than a century of game hunting and habitat destruction, conservation efforts have helped bring back the population of the small sand-colored bird to more than 12,000 individuals.

One breeding pair, nicknamed Monty and Rose, even made headlines in Illinois when Rose birthed the state’s first new piping plovers in nearly 60 years — and forced a music festival to cancel to protect their fragile eggs. While still a threatened species, the piping plover is making a gradual comeback.

To paleontologists, however, the damage to the bird’s legacy may have already been done. These fossil-studying scientists have not yet found a piping plover’s fossilized remains. If none exist on  Earth, and no more are produced, then a society in the far future will never learn of the beach-loving bird’s existence. And humans may be somewhat to blame, according to recent research from Roy Plotnick, a paleontologist at the University of Illinois at Chicago. His work suggests many more species will be similarly lost from the fossil record because of — and replaced by — us.

A piping plover and its chick. (Harry Collins/Adobe Stock)

For the past few years, Plotnick has investigated humanity’s impact on the fossil-making process and the planet by comparing the modern fossil record with that of the past. In a 2016 paper published in the scientific journal Ecology Letters, he and University of Nebraska — Lincoln biologist Kate Lyons concluded a majority of living animal species hadn’t been found in the fossil record but that endangered species were even more scarce. While about 20% of all non-threatened mammals had entries in the record, the same was true for less than 9% of endangered mammals. More dire rates appeared with endangered birds (3.3%) and reptiles (1.6%).

Plotnick and Lyons provide a few explanations for these differing fossilization rates. Species with bigger bodies, wider habitat ranges and larger population sizes appear more often in the fossil record, but hunting and habitat destruction from human activity also play a measurable role.

“We reduce both the range and population size of large animals and thus reduce their chance of becoming fossils,” Plotnick says.

Flooding the record

But humans aren’t only diminishing the likelihood of some species  making their way into the fossil record — we’re also increasing our own chances, along with those of domesticated animals.

For his latest paper, Plotnick and his coauthor, Missouri Western State University geology professor Karen Koy, investigated how human society has altered the processes of fossilization. Animal remains can be fossilized in many ways — turning to stone like most dinosaur fossils, or simply leaving an imprint in rock — but they generally need to be buried or submerged to avoid being eaten, decomposed or otherwise destroyed by environmental forces, Plotnick says. For this reason, paleontologists usually find fossils in previously wet environments such as ancient seabeds, marshes and tar pits.

“Burying things is one great way to make sure that they have a good head start getting in the fossil record,” says Koy, a former Ph.D. student of Plotnick’s who now studies the processes of fossilization, also known as taphonomy. “It protects them from scavengers and sunlight and weather and all sorts of things that can break down bones and materials that you want to fossilize.”

Their results, published in March in the scientific journal Anthropocene, suggest humans will appear much more frequently in the fossil record — as well as domesticated animals. For one, humans have changed the locations that favor fossil creation. Landfills and cemeteries bury bones in dry land where fossilization is normally unlikely to occur. Similarly, mass burying and composting of farm animals have likely ensured the remains of many cows, chickens and pigs will be fossilized.

Human development has also changed the very landscapes that generate fossils. “When farming developed, we drained the wetlands,” Plotnick says. “The damming and the shifting of rivers and the draining of wetlands are going to be a major impact on preservation.”

The numbers also favor more modern humans and domesticated animals producing fossils because there are simply more of them alive. By comparing estimated populations of humans and most other animals in Michigan, Plotnick and Koy found that 9.9 million Michiganders, plus their livestock and pets, outweigh the state’s wild animals 19 to 1. That inevitably will result in more remains than animals not integrated into society. Larger populations, plus easy burial, mean more fossils.

“In terms of sheer numbers, we’re flooding the record,” Plotnick says.

These abrupt changes in the fossil record will be readily apparent to a paleontologist far in the future as a sign of human civilization, according to Plotnick.

“It will be yet another signal of our existence on planet Earth and our alteration of the earth systems,” he says. But while it may be disheartening to think that paleontologist will drown in human and chicken bones while never knowing of the piping plover’s existence, Plotnick and Koy are more interested in how these alterations to the fossil record compare with other geologic times of rapid change: mass extinctions.

A sixth mass extinction?

Paleontologists have identified 26 extinction events in the history of life on Earth, when the extinction of a large number of species in a short period of time occurs. Of those, the disastrous major mass extinctions, often dubbed the “Big Five,” wiped out at least 75% of all species. The most recent was the asteroid that struck the planet 66 million years ago and killed off the dinosaurs. The first occurred 2.4 billions years ago when the oceans filled with oxygen and destroyed most of Earth’s single-celled species, all of which lived without oxygen.

The most recent extinction event is the Holocene extinction — the one we’re causing right now. In the wake of human development and the threat of climate change, homo sapiens are driving a global extinction rate 1,000 times higher than the background rate. The ongoing event has taken on the nickname of “sixth mass extinction” to contextualize today’s environmental crisis, although it’s not yet in the same league as the Big Five. A 2011 study led by Stanford biologist Anthony Barnovsky found 0-1% of animal groups have gone extinct in the human timeline — but 20-43% of species are threatened, his team found. Current extinction rates could lead to 75% of species going extinct within 500 years.

By studying today’s extinction event, Plotnick Koy have been improving our ability to compare the present with the past, says Simon Darroch, a geobiology professor at Vanderbilt University. “What Roy is doing here is trying to extrapolate the future fossil record,” he says. Much like how the piping plover is absent from the fossil record despite not being extinct, Darroch says other animals in mass extinctions don’t need to go extinct — they just have to be too rare to do their jobs, which causes some ecosystems to collapse

“Mass extinctions aren’t really like the signature of mass extinction rate as much as mass rarity,” he says. “So you don’t have to drive a whole bunch of species extinct to them to not perform the ecological roles anymore. What you need to do is just drive them rare, and then they’re not doing all the things that the broader ecosystem is relying on them to do.” Darroch sees this happening in past mass extinctions and expects the same from what’s happening today.

But in some ways, the “sixth extinction” can’t be compared with past events. The species disappearing today are often at the top of their food chains in what Plotnick calls a “top-down” extinction, rather than disruption of the bottom of food chains as seen in all previous mass extinctions.

No other species has ever been the primary cause of an extinction event, nor has one altered the evolutionary paths of so many others. “This is the first time that we’ve had one organism essentially driving so strongly the evolution of other particular organisms and helping them to basically take over the ecosystems,” Koy says.

Because of humanity’s outsized influence on many natural systems, Plotnick believes we’re in geological “uncharted territories”: “Who knows what the heck’s gonna happen long-term?”

Their results are a reminder of the scope of humanity’s massive impact on Earth’s natural systems, changing not only what the planet looks like now but forever leaving a measurable mark in the fossil record. Looking into the past may provide clues for preventing a mass extinction and helping ecosystems recover, Koy says, but no species has had such large influence — or responsibility — in deciding what the planet looks like in the future.

“Going back to biblical things,” Plotnick says, “we are the stewards.”

Photo at top: Archaeological excavations, human skeleton remains, found in an ancient tomb. (Microgen/Adobe Stock)