Sorry to disappoint you, but this story is about Lystrosaurus. That’s him … or her, in that picture above. Yes, this story has the most click-baity of click-bait titles, but seriously, would you have clicked if you knew this was about funny-looking dead reptiles? Didn’t think so. And it’s kind of important.
Because new research on something these guys did a long time ago, can help us figure out how we should invest our efforts today, and what our world might look like in the future. Pretty cool… for a squat little dead reptile.
Lystrosaurs (there were a half dozen or so species) were not dinosaurs. They were therapsids, a group of reptiles that shared a lot of features with early mammals. This guy is more closely related to you than he was to T. rex.
There’s no doubt that Lystrosaurs were … odd. Those two teeth sticking out? That’s all they had. The rest of their jaw was just kind of a beaky thing, more parrot than pig. They had stubby little tails and thick heavy bones. They probably waddled a bit when they walked. They were not sleek, or beautiful, or fierce, or particularly smart.
So why are we talking about Lystrosaurs? Because they were survivors. There was a time, around 252 million years ago, when almost every large animal on Earth died. Lystrosaurs didn’t. In fact, they thrived.
Hang in there just a minute longer. The sex is coming.
Setting the stage
So … 252 million years ago was the end of the Permian Period and the beginning of the Triassic. The Permian was a fantastic period of growth and change. Turtles got their start in the Permian. So did crocodiles and the group that would produce both old school rawr-rawr dinosaurs and the little feathery dinosaurs we call birds. You’ve probably seen models or skeletons of those reptiles with the big sails on their back. Those were pelycosaurs, and the Early Permian had a big variety of them.
Like our friend the Lystrosaurus, the pelycosaurs were in the group of reptiles that would produce the mammals. By the Middle Permian, there were a huge variety of these creatures. Some looked rather clumsy and sprawling, like crocodiles on land, but many had gotten their legs under them, the way mammals do today, and were upright, speedy, and seriously mean-looking.
By the time you closed in on the end of the Permian, the giant supercontinent of Pangea was overrun with a huge variety of animals that would seem utterly alien to us today. The plants (not grass, there was no grass) were grazed by giant, stocky turtle relatives called Pareiasaurs that ranged to well over 1,000 pounds. Speedy and lightly-built Gogonopsids, that ranged from cat-size to wolf-size and bear-size, hunted the diverse herbivores through forests of tree ferns and conifers and across fields of towering giant horsetails. There were lakes holding amphibians as big as crocodiles, and crocodiles who came out of the water and learned to run. Out in the oceans, trilobites still lived as they had for more than 200 million years, but there were also lots of new types of fish and even sea-going amphibians. Bugs. Lots and lots of bugs. It wasn’t the Earth you know, but it was a rich, diverse ecosystem bursting with possibility.
Then it all went to hell.
So … what happened?
Global warming happened. A set of volcanoes in an area called the Siberian Traps, up at one end of that big single continent, started erupting and just didn’t stop. Those volcanoes erupted for something on the order of 300,000 years, stopped for a bit, then did it again for nearly as long. They piled up a lava a couple of miles thick over a million or more square miles. They pumped out about 30 trillion tons of carbon. Toward the end of that period there was a sudden spike in CO2 that seems to be far more than the volcanoes could have produced. There’s been speculation (and some evidence) that the world might also have had an impact event. Or two. Or that the volcanoes set fire to existing reserves of coal or oil. Something happened in a hurry. It was bad.
At the very beginning of the Triassic Period, the Earth nearly died.
In a very short period, the carbon in the atmosphere more than tripled. Maybe it was existing fossil fuels being burned. Or it could have been all the methane stored in the ocean was suddenly driven into the atmosphere by temperatures that had risen slowly to that point. Or the source may have been a mechanism we still don’t understand. We know it made carbon, and a lot of it.
Even before this sudden event, something else had gone wrong—the ocean went sour. So much CO2 soaked into the sea that the ocean’s chemistry became acidic. This killed off most of those things that have shells, like clams, and most of those things that build structures, like corals. The oceans of the time started to look like oceans from millions of years earlier, with nothing living on the sea floor but simple sponges. The lack of those shelly things, and the already acidified water, meant that the ocean couldn’t act as a buffer for carbon when whatever happened, happened.
You had high CO2. You had rising temperatures. You had an ocean that was growing more acidic. All these things were already stressing the environment, causing extinctions both on land and in the sea. Then bang. The Great Dying.
Today, the hottest points in the ocean approach 90 degrees. It’s this kind of warm water that leads to the formation of hurricanes. At the very end of the Permian, the average temperature of the ocean at the equator got up to around 104 degrees. The weather that this scalding water produced was … we don’t know. It was probably incredibly bad.
As the temperature went up, the hot, acidic ocean also lost oxygen. At 104 degrees, sea water can hold only about half as much oxygen as cold water. This steaming toxic soup was tough on living things. Nearly all the fish died. Even simple things like worms died. Not everything that lived in the ocean bit it, but about 96 percent of everything vanished. Even those sponges that had taken over when everything else was gone, couldn’t take it. They died, too.
On land, average temperatures went up more than 14 degrees Fahrenheit. it was so hot that there was essentially a dead zone on either side of the equator where almost nothing lived. For a while there, it was North Earth and South Earth, divided by a wall of heat.
It was the closest the world has ever come to tipping over to where the carbon cycle falters completely, volcanic gases keep building up, and next stop is Venus.
If you’re wondering how the Siberian Traps compare to CO2 production today, we pump about 40 billion tons of carbon into the atmosphere each year. While the big burst of CO2 that’s poorly understood right at the start of the Permian was bigger, the total production from the Traps volcanoes to that point was about 30,000 billion tons. Take one deep breath in relief as you realize it would take us 750 years at the current rate to match the output of the Siberian Traps. Feel comforted? Yeah. Don’t. Notice the other part—the part where it took 500,000 years or so for the Traps to get that gas out there. We’re pumping out carbon at a rate nearly 700x faster. And rate matters, because the faster you put out carbon, the more you overwhelm those systems (plants, the ocean, etc.) that take it in.
The best climate models don’t predict us reaching anything like what happened at the end of the Permian. But then, we don’t know whether the slow buildup over the Permian led directly to the sudden rise at the start of the Triassic. Personally, I wouldn’t bet my planet on it.
As the Permian came to a close, the giant amphibians died out in the streams. The trilobites that had been swimming in the ocean for 250 million years died out. So many different kinds of plants died out that the end of the Permian is just about the only time since land plants developed where there are no coal deposits. There simply weren’t enough plants left. Two-thirds of all the mammal-like reptiles became extinct. Even insects suffered a major extinction, which is something that’s never happened since.
It was a very empty, hot, awful world at the start of the Triassic, with poison seas, steamy, CO2-choked air, sparse vegetation, and even sparser animal life.
But Lystrosaurs did fine. They did great. In some fossil beds, 90 percent of everything is Lystrosaurs.
Do you know why? That’s okay. Neither does anyone else. And that’s why were here today.
About those lystrosaurs
Now, back to the stars of our show. And the sex.
Lystrosaurs had it. Sex. All reptiles did. Still do. While amphibians can follow any path from frog on frog action to a fishy swim-by of floating eggs, reptiles don’t really have a choice. Like birds, Lystrosaurs and their Permian pals all practiced internal fertilization. Lystrosaurs got it on. The important thing is when they had sex. And finally (I can hear you saying it with more emphasis, finally) here’s what all this has been leading up to.
In a new study published at nature.com Science Reports, researchers have found something about lystrosaurs that no one really put together before. Turns out their secret sauce might be something we’re seeing in the world around us, right now.
If you look up a Wikipedia article on Lystrosaurus you’ll see it described as “approximately the size of a pig.” Other places will say “the size of a dog.” The images show an animal about two feet long, weighing in at about 20 to 30 pounds. But that’s not the case. Or at least it wasn’t always.
When lystrosaurs first appeared, they were larger. Much larger. Those early lystrosaurs were closer to 10 feet long and weighed several hundred pounds. They were big, bulky, buffalo-sized animals.
There was something else worth noting. In looking at early specimens of Lystrosaurus, the researchers found growth rings in their bones indicating that the animals lived 13-14 years. But when you come to the big extinction period and the period immediately following, everything changes. At that point, the lystrosaurs really were dog-sized. They were also only two to three years old, max.
Still, there were lystrosaurs. Lots of lystrosaurs. So during the disaster period, lystrosaurs were not just dying sooner, they were breeding sooner—at a size and age that would have made them juveniles during earlier times.
Previously, paleontologists had looked for something special in the structure of Lystrosaurus that explained why the animals survived an event that killed so many others. Did they have super-duper lungs better suited to the nasty air? Maybe some kind of keen cooling system that made it possible for them to operate in broiling heat. Maybe… whatever people were looking for, they didn’t find it. Lystrosaurs were just chunky little reptiles at the border with mammals. There didn’t seem to be anything particularly special about them.
But the way Lystrosaurus responded to the crisis … that was special. The ability to breed smaller and younger is a decided advantage for an animal under strong pressure. First, smaller animals need fewer resources. If a lystrosaur only needed to be dog-sized to reproduce, it could do so even in areas where there weren’t enough resources to support the cow-sized variety. This kind of size-reduction happens in a lot of situations where animals are placed in environments where resources are limited. Second, animals that can produce younger simply don’t need to live as long. So if you’re in conditions where the odds of something happening to knock your little parrot-beaked brains out is high, there’s a real advantage in reaching maturity sooner. In human terms, lystrosaurs became capable of reproducing at kindergarten age—and cut their lifespans to about about the fourth grade.
That rapid turnover may have also given lystrosaurs another advantage: rapid turnover. By churning through generations several times more quickly, selective pressure could work on the population more rapidly, a feature that’s pretty desirable when conditions are not simply bad, but in a state of flux.
It’s not just pig lizards
The researchers note that other animals may be reacting in the same way to a high stress environment. For example, the Atlantic Cod, which has been heavily over-fished (because of extreme tastiness) has been found to be maturing sooner and growing to a smaller size.
Though not mentioned in this paper, the Virginia Opossum (yes, that’s a plain old possum) is another candidate for an animal that’s taken the breed young, die fast route. While a raccoon can live 20 years and a rabbit more than 10, possums rarely make it to two before reaching advanced decrepitude. Possums may have suffered a recent period of high predation, or they may be directly affected by that No. 1 source of early possum termination: getting flattened by a car. Or it may be that breeding like a possum is working for these delightful why-the-hell-did-we-get-stuck-with-snarly-rat-things-as-our-only-marsupial since possums are expanding their range.
Who will survive?
In any case, the most important thing to get from this paper is probably its predictive property. Right now, we are in the middle of a major extinction event. This event is caused by us. Not just us making things warmer, but us eating all the cod, making coats out of all the megafauna, replacing buffalos with beef cattle. Just being basically everywhere. We’re having a high impact on the environment, one that’s affecting animals of all types and sizes.
When thinking of which animals are most likely to be hit hard, we should look at those which reach sexual maturity very late. Elephants don’t become mature for at least a decade. A rhino takes a good seven years. A blue whale may not be mature until around 15 years.
These animals are going to be slower to respond to increasing stress. Give them half a million years of slowly tightening the screws, and we might see mini-elephants and rhinos that chopped their maturity period down to a couple of years (and their size and lifespans along with it), but we’re not giving them that slow, steady push. Even in the worst case scenario, if lystrasaurs held onto their bigger size right up until the 10-50,000 year Big Extinction Event, they still had about 5,000 generations to work on downsizing. Elephants aren’t getting that luxury.
Big animals that are slow to mature always have a hard time with extinction events (see dinosaurs, rawr-rawr variety). Not stressing these creatures beyond their ability to survive is going to take work—a lot more work than we’ve been putting into it so far.
On the other hand, the possums will probably be fine.
A few notes
I interchanged “lystrosaurs” meaning the animals in the group with “Lystrosaurus” meaning the animals in the genus, Lystrosaurus. For the most part, these two terms mean the same thing, though there is one species that is generally thought to be a lystrosaur but which is currently not classed in the genus. I just got tired of throwing the italicized version at you so often.
Raccoons out in the wild have a life expectancy of only about three years, but don’t be deceived. Raccoon numbers are pulled down by very high infant mortality. Probably a good thing, as my trash cans couldn’t take any more of the things. Racoon not eaten as babies live long enough to become those things that figure out how to open the storage locker on the deck and eat 40 pounds of sunflower seeds in a week. Possums simply get old at two. Their clock runs out.
The math on how our CO2 production compares to that of the P-Tr boundary volcanoes is my own. Meaning you should really wait to see it somewhere else before you base a book, policy, or even a heartfelt tweet on these numbers. The total amount of CO2 released over the entire extinction event was much greater, on the order of 85,000 trillion tons. Which is… a bunch. Spread that out over the whole 500,000 years and you’d still have several times more than we’re producing today. The question is: did the long release at the end of the Permian trigger the rapid shock at the start of the Triassic? So far as I’m aware, no one yet has an answer.
Lystrosaurus doesn’t actually mean pig lizard. It means shovel reptile. But just look at them. I rest my case.
The entire article is available as an Open Science article and makes for interesting reading, but it can be tough sledding. Here, try this:
The most striking difference between Permian and Triassic therapsids is that the former had substantially more growth marks than the latter; this difference is significant even after accounting for inter-elemental variability (p < 0.0001), as well as phylogenetic relationships and body size differences amongst taxa (phylogenetic generalized least squares regression with mean number of growth marks as the dependent variable and BSL as a covariate; adjusted R2 = 0.4058).
If that didn’t phase you, then cool. Go read it. I could seriously use someone to double-check my understanding.