It’s a bit unorthodox, reaching out to those who spend their lives studying the past and asking them to predict the future. But these paleontologists were happy to take on our assignment: Could you apply what you know about how life has changed over time to guess what species might be like millions of years from now?
The goal was not to predict the future with 100 percent accuracy. Instead, we wanted to understand what processes shaped life on Earth before today and how those same factors could change life down the road.
One of the scientists we interviewed explicitly mentions the interconnectedness of all species on this planet. If we pull that string a little more, we know that nothing exists today by accident. Everything we know now is the result of everything that came before us. It’s a staggering mental exercise: trying to grasp the eons of time, change, and evolution that have brought Earth to this point.
The question is: What comes next?
Stephanie Drumheller, paleontologist in Earth and Planetary Sciences at the University of Tennessee:
Alligators and crocodiles have a reputation for being “living fossils” who “haven’t changed since the time of the dinosaurs.” This particular turn of phrase is a great way to make croc paleontologists rage, because it doesn’t actually take much digging to find a lot of fun weirdness in the croc family tree. There have been fully marine crocs with flippers and fully terrestrial crocs with long, running legs. There have been omnivorous and herbivorous crocs, with funky, specialist teeth and weak little jaws. There were heavily armored crocs, crocs with broad, flat heads and little peg-like teeth, tiny crocs, giant crocs, just all kinds of wacky stuff. If you go far enough back in the family tree, you even get distant croc-relatives that walked around on two legs and looked kind of like dinosaur-mimics.
What’s driving the idea that crocs are unchanging is that we’re looking at a low stand in their diversity right now, and the living crocs all have variations on the semi-aquatic ambush predator body plan, where they pretend to be a log and pop out to surprise prey. Fossil croc-relatives also filled those roles in their ecosystems going all the way back to the age of dinosaurs, but it definitely wasn’t the only niche they filled.
We can look at how croc diversity changed through geologic time and map that against climate, to understand why we see more diverse crocs in some periods and less diverse crocs in others. In the broadest sense, when the climate gets warmer, crocs seem to spread out and diversify. We find croc fossils at really high latitudes when the paleoclimate was warm. When it gets cooler, lineages die off and the survivors become concentrated in warmer regions. Geologically speaking, we only recently came out of a glacial period, so we’re looking at a modern diversity that just went through a rough patch.
It’s hard to predict what might happen in the future, but it can be fun to speculate. One of the interesting things about crocs is that all of that odd diversity I mentioned isn’t super restricted in the family tree. By that I mean, there isn’t just one branch of the family tree with all of the marine crocs, or one branch with the omnivorous ones, or one branch of the surfboard heads. They pop up all over the place. So crocs are pretty adaptable, and they sometimes move into ecological roles you wouldn’t expect, especially if your basis for comparison is only the modern survivors.
In the distant future, I could see crocs filling some of their funkier paleontological roles again: marine, terrestrial, filter feeding, herbivorous, etc. They’re very good at filling unexpected niches, and they’ve proven themselves to be survivors in the past.
I think we’re going to see crocs on the move in the near future. As one example, American alligators are a real success story for conservation; people sometimes forget that they used to be classified as endangered. We’re already seeing them expand their range. You can actually find wild alligators in places like Oklahoma, which blows people’s minds.
Ashley Leger, field director at Cogstone Resource Management:
There has always been a cycle to paleontology, and, in my opinion, it can be linked to one constant: climate change!
Our planet’s current rate of climate change is unprecedented and is strongly due to anthropogenic factors. Because of the human aspect—I’m not sure if this is going to happen in 1,000 years, 100,000 years, or millions of years—I think we will start to see some distinct changes in the flora AND faunas of the Earth. (If I had to guess, I think it’ll happen sooner, rather than later.)
As the Earth gets hotter, plants are going to start to slowly change. Coniferous trees are going to struggle. Palm trees and cacti are going to flourish. Grasslands are going to start slowly shrinking, and things will become more and more arid. There will be abundant life near sources of water, and that is where most of the rich, green vegetation is going to thrive.
Mammals: I believe the megafauna animals (and I’m including everything from deer to elephants) face one of two options. They will either go extinct, or they will shrink. There will not be enough vegetation for them to maintain their large body sizes, and they will get smaller and smaller.
In the Oligocene, there were deer that were only about 12 inches tall. I think if the large mammalian population is to survive, they will get considerably smaller over time. The determining factor between shrinking and extinction, though, will be directly tied to the rate at which we change the climate. If it continues at the current rate, extinction is most likely. If we can slow the rate of climate change, megafauna *might* have time to adapt and shrink. I also think mammals with adaptations already for warmer climates will do much better in this evolving world. Body size will shrink, fur will get thinner and shorter, eyes will get smaller (to reduce water loss, because in a hotter environment, moisture can be lost through eyes), ears will get bigger (for cooling and listening for where food is), and tails will get longer because there will be more bugs to swat away.
For specific examples, African elephants use their giant ears to keep them cool. Their ears are full of tiny blood vessels and they flap their ears when it’s hot to cool the blood. They’re already better adapted to heat. Thus, African elephants will be more likely to survive and adapt (aka become smaller) than Asian elephants. Polar bears are doomed, but the sun bear, which is more well adapted to heat, will likely adapt. Animals with shorter coats (like antelope) will do better than animals with longer coats (Rocky Mountain goats). I think any mammals primarily adapted to cold environments will go extinct. Those in the temperate climates have a chance at adaptation.
Birds: I think birds are going to become larger. Since they are so mobile and can fly to new areas, they will have a better chance of finding food. Plus, if mammals start getting smaller, this means there will be more small animals for birds to eat. Thus, I think the birds get larger, with bulkier breast muscles to be able to fly farther and farther. I also think eggshells will become much thicker to protect against the heat.
Fish: This is tricky! Water takes a longer time to assimilate a new temperature regime. I think the faunas of the ocean will remain relatively constant for a long time. Some of the larger creatures will struggle, though, because of their food sources. The blue whale will have a hard time maintaining its large body size, and animals like orcas and sharks that eat a lot of seals will also struggle. I think the seal population will diminish, and so orcas and sharks will have to shrink. The very deep-sea creatures are likely facing extinction. Once the ice caps have melted, there will be no influx of sinking cold water. I think the deep-sea creatures will not have time to adapt and will go extinct. Bye coelacanths.... for real this time!
Reptiles: I think the lizard population is going to explode. These cold-blooded animals are so well-suited to warm temps that I think they are going to thrive. I think there will first be a massive increase in the population of small lizards, and I think they will start adapting and have larger body sizes. As the rest of the populations struggle, there will be more and more insects for the lizards to eat. Plus, if the birds get larger, lizards will get larger, too, so they are not as easy to eat. I think speed will also start to be an adaptation that will be desirable. If the lizards are abundant, they will start naturally selecting for speed. The strong, fast lizards will be the ones that escape the birds.
Insects: This creeps me out to think about. A lot of insects really love hot and humid weather. If the planet keeps heating up, more ice caps will melt and there will be more and more water to try and absorb the heat. As that happens, more and more water will evaporate, and Earth will become very humid. Thus, the insect population will explode. This will also fuel the reptile population that will be feasting upon all these bugs. And that’s all I have to say about bugs, because now I’m itchy.
I think humans have done a major disservice to our planet. I think Mother Nature is a tough ol’ lady, and she’s going to fight back. I really believe that we could be facing another megafauna extinction right now. And honestly, the other animal species of the Earth will do better if humans go extinct. We destroy so much natural habitat, and we hunt everything. If mammals (think deer, elk, moose, bear) that are hunted keep getting smaller, humans will be hunting more and more.
If I had to put my money on one species to pull through, I’d be betting on horseshoe crabs. If you look at horseshoe crabs through time, they have changed very, very little. They are, in my opinion, the “perfect” species. They don’t get terribly large, so they can maintain their diets; most of their exposed body is shell for protection; and they live in the water, which will change more slowly, giving them more time to adapt. Plus, their blood is so unique and seems to carry healing properties that cannot be duplicated in labs. I think something about these amazing animals has them slated to do very well, no matter what our planet undergoes.
Jingmai O’Connor, paleontologist; senior professor, Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences:
When we talk about a mass extinction, it usually lasts 5 million years. We can actually see this within the geologic record. We see rock all over the world that records a 5-million-year period devoid of any life. In other words, you see all of these fossils, this rich diversity, and then suddenly, you hit this extinction zone and everything is gone. Then after 5 million years, everything is back, although, of course, with a slightly different fauna. We talk about these theoretical places that we refer to as “refugia,” where we know that certain lineages must have survived. When conditions were right again, they returned back to normal population levels. Refugia are not in the fossil record, but we know things survived.
After the end-Cretaceous extinction, which occurred about 66 million years ago, large dinosaurs were wiped out. But one lineage of birds survived. I don’t mean just one species of bird; there were a bunch of species within one lineage. And that lineage, which is called Neornithes—crown birds, essentially—exploded in diversity after the extinction into the huge diversity of birds alive today. Birds are the most diverse group of vertebrates on land. After these large carnivores, the dinosaurs, went extinct, then birds evolved to occupy that niche. A great example in the Paleocene is these large birds that are called “terror birds” (Phorusrhacids). They were flightless, and they had skulls up to 1 meter long! They occupied this ecological niche of the terrestrial predator that was formerly occupied by non-avian dinosaurs.
I envision that something like this would probably happen again. Wipe out all the large mammalian predators and birds will surely survive. In the absence of other predators, birds might start walking around on the ground more; they wouldn’t have to fly to get away. And if birds don’t need to fly, they could increase in size. Flight restricts your body size. You have to be really light to be able to fly because flying is very energetically demanding. So then we’ll probably have something like the terror bird back, which is a neat thing to think about.
It’s been demonstrated that we’re in this sixth major mass extinction and that this is the first mass extinction caused by one species actively destroying its environment. One question posed was, will higher intelligence evolve again? Everything is about survival, and if our intelligence leads to a mass extinction, then my argument is it’s not necessarily good for survival. We are probably going to wipe ourselves out. It’s unlikely that such intelligence is going to rise again, especially as we’re wiping out all of these other lineages that also have enlarged brains. We actually behave like a virus. A virus multiplies in its host until it kills its host. That’s what we’re doing. Of course, I love humanity. I think it’s amazing, a lot of the things that we can do. But one thing that I’ve always said is that humans are just extremely myopic. We’re not looking at the bigger picture: what we’re doing and how we’re going to deal with the problems we’re creating. So, we do have this intelligence, but we’re not utilizing it in a way that is actually intelligent.
I’m a fatalist. I don’t believe humans have any hope. We’re definitely doomed. And unfortunately, we’re taking a lot of things with us. That’s the most unfortunate and tragic part: We’re devastating this beautiful Earth. But, as paleontologists say, in 5 million years it’s all going to be normal again!
Jessica Ware, assistant curator at the Sackler Institute for Comparative Genomics at the American Museum of Natural History; assistant professor at the Richard Gilder Graduate School; president of the World Dragonfly Association; and vice president of the Entomological Society of America:
All of the species on the planet are interconnected.
You could imagine a future where there would be the drop out of some taxa, opening up niche states, and then the rise of, maybe, lice. Right now, they’re inconsequential—maybe not inconsequential, they’re a nuisance—but in terms of a species number, very, very small!
We have a couple different types of lice that can be on our body. As long as there’s that food source, there will probably always be room for them to diversify. But if, in the future, humans aren’t still here, then circumstances would change for that specific type of lice.
You can basically track human migration by tracking where these lice have gone. But if humans aren’t moving things around, then that species of lice becomes isolated, and when isolated, they accumulate mutations. Background mutation occurs constantly in life, but if you imagine two populations separated by a river of lava, say, then the accumulated mutations will eventually differ between the populations; this is a kind of speciation.
If birds and other mammals survive into the future, continuing to provide a food source for lice, who knows? Maybe it will be the rise of lice!
I think that so much of human existence has been focused on documenting things that are like us. We love things that are tetrapods. We love things that have four legs. Insects, even though they’re the most abundant organism on Earth, they’re just so poorly appreciated. There are hundreds of thousands of species of flies! They have very fast mutation rates; there are constantly new species being described. By comparison, there are only 6,000 species of dragonflies, and only 2,900 species of termites.
While everything is constantly undergoing evolutionary processes, such as the radiation, or the diversification, of species, perhaps we are just seeing the tip of the iceberg of the major radiation of flies. Maybe they’re in the process of this big species explosion. Especially in the absence of humans, since we are always trying to eradicate them, maybe flies are going to be the next big one. There are so many strategies that they have: some drink blood, some are scavengers, some are fruit-feeders, some are pollinators, some are predatory. They fill a lot of different niches, which evolution has proved increases survival.
Phillip Barden, paleoentomologist; assistant professor at the New Jersey Institute of Technology
I specialize in social insects in the fossil record, mostly ants and termites. When we’re talking in terms of biological success, we usually talk about three metrics: diversity, biomass (the amount of total abundance), and longevity (how long a lineage persists without going extinct).
In the case of social insects, the reason why their biomass is so high is because of the eusocial behavior. Only one or a few individuals do all of the reproduction. This not only means that they’re efficient, it also means that they are able to sustain a lot of casualties. It’s not a big deal for an ant colony that has 10 million individuals to lose 10,000 individuals every day. It’s like you shedding off your dead skin cells.
Lineages that only appear for a brief time we might consider to be less successful than those that appear in the rock record for tens or even hundreds of millions of years. In the case of termites, they are the original societies and evolved social behavior in the Jurassic, as far back as 150 million years ago. The oldest ant fossils are about 100 million years old. Put another way, the amount of time between the first termite colonies forming and Tyrannosaurus rex is greater than the amount of time between T. rex and today.
We know from a recent global estimate that the biomass of termites is probably about on par with the biomass of all humans alive today. So they have these really remarkable impacts on environments, and they, themselves, tend to cause ecosystem changes. Think, for example, of all of the organisms that eat ants and termites.
I think insects are going to do really well in the very long term, once it gets warm broadly around the planet. Insects tend to like it hot. The highest diversity we find in insects is in the tropics. The highest biomass is in the tropics. And, should the planet become largely tropical, then I think insects are going to have a good time millions of years in the future. Things like ants and termites will probably continue to diversify, and they might persist all around the planet. If that’s the case, they might shape other organisms by indirectly making more species of ant- and termite-feeders, or future species may join the 10,000 estimated species of invertebrates today that make a living by mimicking ants or exploiting resources within an ant colony.
The maximum body size of insects is restricted because they don’t have lungs; they respire passively. The surface area of all the internal tunnels that infiltrate their body is a hard constraint on how big they get, unless you increase the amount of oxygen that’s present. Some of the insects that we had in very Deep Time were able to get large because of an increased amount of atmospheric oxygen. An example is Meganisoptera, or griffinflies. They’re relatives of modern dragonflies that had 2-foot-wide wingspans. Their massive size is tied to increases in oxygen approximately 300 million years ago.
More recently, Earth experienced the Paleocene-Eocene Thermal Maximum (PETM), which was the hottest that Earth had ever been in the last 55 million years. In the fossil record, around the PETM, we find these enormous ants about the size of hummingbirds. They’re only present around this period. And the really cool thing about them is that they are found in fossil deposits that are in high latitudes today (for example, Germany). That suggests, along with some other paleoclimatic evidence, that the reason these massive ants were able to live so far north was because it was really warm.
Today, the only places you find the largest ant species—the ones that are about the size of your thumb—are in the tropics. And it’s probably not a coincidence that the places we find fossil ants that are even larger than the largest ants we have today are in areas we estimate were also very hot millions of years ago. Therefore, if, in the future, the entire global temperature increases, it seems likely that we’ll see not only larger insects, but larger insects in more places than we see them today.
We already know from the fossil record that local extinction—that is, extinctions that are restricted to certain geographic areas—drives a lot of the patterns we see in biogeography. The classic vertebrate example are camels. You only find camels in Africa, the Middle East, and Eurasia today (although llamas in South America are also camel relatives), but we know from the fossil record that they actually originated in North America. They went extinct in North America. If we have these great changes in climate in the future that shift the ecosystems that we know about today, there may only be these small pockets of refugia left on the planet that certain insects can live. It would be fun, but also depressing, to think about ladybugs only living in Greenland or Patagonia or other extremes where it’s likely to be less warm.
Another interesting idea to think about is that some of the stereotypical things we think of insects doing today might be done in the future by a different group of insects that takes over that niche if the current occupants go extinct. If it turns out that bees are particularly prone to extinction in the future, there might be other types of pollinators that fill in those specific niches. The fossil example is Kalligrammatidae. They were, essentially, butterflies in the Jurassic. They are actually not related closely to butterflies; they are more closely related to what are called lacewings, those little green things that stick to your screen door in the evening. They convergently evolved a lot of the same traits that we see in butterflies: they have a proboscis, they even have spots on their wings. Those were actually the original “butterflies,” but they went extinct, and modern butterflies filled in that niche.
Alexis Mychajliw, paleoecologist; postdoctoral research associate at the Laboratories of Molecular Anthropology & Microbiome Research at the University of Oklahoma; and research associate at the La Brea Tar Pits & Museum:
How we think about the future really goes back to what we understand about the past—not just specific baselines of biodiversity, but when you zoom out enough, you see the same experiments played out across Earth’s history: temperature change, sea level rise and fall, carbon dioxide variations, and in turn, responses from biological communities as species either move, adapt, or die.
We don’t need to extrapolate much to show that as our planet warms due to human activities, sea levels will rise around the world, because water that was locked up in glacial ice is now melting. This, of course, has catastrophic consequences for island nations and low-lying coastal developments, many of which are already unfolding before our eyes.
Sea levels fluctuated in the past as well, particularly during the Pleistocene (approximately 2.8 million years ago to 11,700 years ago), which was an epoch shaped by recurring glacial cycles: as temperature and ice cover changed, so did sea level. This resulted in many islands growing larger or smaller over time, sometimes being connected to continents through “land bridges” or even being connected to each other, if they shared the same underlying bank. The logic of the species-area relationship indicates that we would expect bigger land areas to support a greater diversity of species at any one given time. This recent history of sea level change is one of the reasons why islands today are incredible places to study evolution for their unique histories of isolation and colonization, and also places of global conservation importance for harboring so many endemic species.
We can also appreciate that islands were evolutionary cradles and places where, quite frankly, things got weird. So, in a thought experiment fast-forwarding thousands of years, let’s imagine that sea level has risen because of anthropogenic climate change. Let’s imagine that it’s taken places that were once contiguous pieces of land and broken them up into islands of varying shapes and sizes. What would happen to the evolutionary trajectories of the mammals cut off from their larger populations?
From studying extinct island mammals, scientists have developed a hypothesis, known as the “island rule,” but what I prefer to consider as the “Alice in Wonderland” effect: drinking the potion, normally large mammals get small (island dwarfism), and eating the cake, normally small mammals get big (island gigantism).
Proboscideans (elephants and their relatives) have given us great examples of island dwarfism because they are excellent swimmers and reached many islands in the past. The California pygmy mammoth, for example, evolved as a result of Columbian mammoths swimming over to the Channel Islands during sea level lows and grew to just 4 to 8 feet at the shoulder! The Mediterranean islands (e.g., Crete, Malta, Cyprus, and others) are well known for their diversity of extinct dwarf proboscideans, and it has been intriguingly posited that one of their skulls inspired the Greek legend “cyclops.”
In the Caribbean, relatives of giant ground sloths reached places like Cuba and Hispaniola and evolved over millions of years to become the size of monkeys or small dogs. Imagine having one of those on your shoulders! In the future, could we have more pint-sized proboscideans? What new myths and stories would they inspire?
Now time for my favorites. On the flip side, just as you have big things growing small, perhaps because of resource constraints, you also have small things getting big. Maybe it’s because they are suddenly freed from the pressures or predation and competition or have new resources to use. Whatever the cause, the results have been awesome. Let’s go over a few.
If you found yourself in Gargano (Italy) during the Late Miocene, you would actually be on an island, rather than a peninsula. And you’d have to watch out for the fearsome Deinogalerix koenigswaldi, a GIANT MOONRAT! Moonrats, also known as gymnures, are non-prickly hedgehogs that are normally about the size of a large rat. But Deinogalerix was about the size of a dog and was likely a carnivore, rather than insectivore. Nearby Sardinia also had an extra-large pika.
In the Caribbean, during the Pleistocene, you could have found Amblyrhiza inundata, a giant rodent and distant cousin of the guinea pig, that would have weighed anywhere from 100 to 400 pounds! It lived during a time when many of the small islands of the Lesser Antilles, such as Anguilla, were much larger or even connected to each other. As sea levels rose, these islands disconnected and shrunk and were likely just too small to support a megafaunal rodent.
There are many more instances of species drinking the potion or eating the cake on islands, especially those whose effects were more subtle, such as the still-extant Hispaniolan solenodon, which is about the size of a house cat and one of the few venomous mammals in the world. At 1 kilogram, though not seemingly “giant,” it is more than 10 times larger than your average shrew.
Unfortunately, in many of these cases, these fantastic island species went extinct not due to environmental change but human arrival. So, any future we foresee of spectacular evolutionary potential caused by isolation and divergence on the myriad hypothetical islands created by sea level rise must also mean that we humans give species the space to embark on their evolutionary journeys.