200 million years ago our planet was hotter, wetter and super-duper dinosaury

Science | Gregory Beatty | March 10, 2022

The third installment in the Jurassic World trilogy, Dominion, hits theatres June 9. The setting is modern-day Earth, the same planet as when the movie’s dinosaurs actually were alive. But our “world” is much different than the one they inhabited.

If we don’t start getting serious about climate change, though, Earth, over the next few centuries, will become decidedly more Jurassic-like.

The transformation has already started. And so, with a cautious eye to the future, let’s look back on what Jurassic Earth was like.

Middle Mesozoic

The Jurassic is the second of three periods that make up the Mesozoic Era (or Age of Dinosaurs). The periods include the Triassic, which ran from 251.9 million to 201.3 million years ago; Jurassic (201.3 million to 145 million years ago); and Cretaceous (145 million to 66 million years ago).

The Cretaceous, of course, ended with a mass extinction which brought the Age of Dinosaurs to a close. The Triassic ended with a mass extinction too — although ironically, end-Triassic actually benefitted dinosaurs.

The cause wasn’t a giant asteroid slamming into Earth, as with end-Cretaceous. Instead, end-Triassic was triggered by the break-up of the 135-million-year-old supercontinent Pangaea into two huge land masses: Laurasia (comprised of North America, Europe, central Asia) and Gondwana (South America, Africa, Australia, India, Antarctica, Middle East).

The break-up was driven by plate tectonics, with Earth’s mantle turning over more vigorously, melting rock and producing major volcanic eruptions, says Donald Henderson, curator of dinosaurs at Alberta’s world-renowned Royal Tyrrell Museum.

“In recent times we’ve had major eruptions such as Pinatubo (Philippines) in 1991 and Grímsvötn (Iceland) in 2011,” says Henderson. “But those are just pinpricks compared to what happened at end-Triassic. It’s a combination of ash darkening the skies, and carbon dioxide, sulfur dioxide and other compounds being put into the atmosphere which changed the chemistry.”

Pangaea’s break-up into two supercontinents disrupted long-established ocean currents too, further destabilizing weather patterns in an already stressed plant and animal habitat.

“In western Canada, we have some of the biggest ichthyosaurs from the late Triassic,” says Henderson. “They were probably filter feeders like whales today, so if the microscopic fauna get clobbered that trickles up the food chain. None of those marine giants, which were 25 metres long, made it across the boundary to the Jurassic. Only smaller ichthyosaurs survived.”

That was true for land animals too, says Henderson. “There were a whole bunch of bizarre creatures that lived in the Triassic but the environmental changes were so severe that large amphibians and bulky reptiles like aetosaurs and rauisuchians got clobbered too. They were heavy, six-metre-long animals at the top of the food web.”

Dinosaurs at end-Triassic were mostly small and lightly built. The predator coelophysis, for instance, was the size of a large turkey. Dinosaurs also had quicker generation times and could eat a greater variety of foods. All that gave them an evolutionary edge in surviving the changes wrought by Pangaea’s break-up.

“Somehow dinosaurs made it through, and in the early Jurassic you suddenly see big dinosaurs like vulcandon which is 12 metres and weighs many tonnes,” says Henderson. “A close relative of coelophysis, the dilophosaurus of Jurassic Park fame, is four to five metres long. And that’s early Jurassic. It didn’t take long for them to diversify and fill all these ecological niches.”

As CO2 and SO2 accumulated in the atmosphere from all the volcanic activity, global heating kicked in, and temperatures soared to between five and 10 degrees C warmer than present-day.

“They’ve made climate estimates for western North America from the late Jurassic when famous dinosaurs like stegosaurus and diplodocus were around, and 40 degrees C was a typical summer temperature,” says Henderson. “It’s thought there were forests close to the poles. There still would have been a polar night, but there were no polar icecaps.”

At best, there may have been some alpine glaciers. But with no icecaps, sea levels on Laurasia and Gondwana were 75 to 140 metres higher than today.

Although that wasn’t all due to climate change, says Henderson.

“Sea level depends on the amount of water available. But there is also the ocean basin volume, and it changes during the Jurassic, [because] when Earth’s mantle starts to convect vigorously it lifts the mid-ocean ridges and basins get shallower. The water has nowhere to go except to spill onto the continents.

“That happened a lot during the Jurassic, which is why we see a sudden radiation of all sorts of marine reptiles because there’s all this new shallow warm habitat,” says Henderson. “It’s not just reptiles, there are fishes, invertebrates and other marine creatures.” [see sidebar]

On land, conifers were the dominant plant form — angiosperms, or flowering plants, didn’t evolve until the early Cretaceous.  Spruces, cedars and pines are modern conifers. Besides trees, there were ferns and cycads, which are tree/fern hybrids.

Given the woody nature of the flora, plant-eating dinosaurs in the Jurassic were more arborivores than herbivores. 

“There’s a western North American dinosaur called camarasaurus that has really strong, stubby teeth,” says Henderson. “It’s a medium-size sauropod, but people have looked at the scratch marks on the enamel, and it was clearly eating tough, gritty food.

“One reason it’s thought those dinosaurs got so big is they needed a big stomach or system of stomachs to digest this material,” he says. “They had to keep the ferns, cycads and conifers in their gut for a long time to extract nutrients, likely with the aid of bacteria or another microorganism.”

As the sauropods grew in size, it led to an arms race with theropod predators, says Henderson.

“Predators could probably take down juveniles and hatchlings but the largest sauropods, as adults, were basically attack proof,” he says. “Predators would’ve scavenged them though, as a ten-tonne carcass lying on the landscape is just a resource waiting to be exploited with pterosaurs flying in and beetles laying eggs for maggots to eat the flesh.”

The Last days Of The Jurassic

Large animals that need a lot of habitat. Where have we seen that before? Oh right, at end-Triassic when giant croc-like reptiles went extinct. Nothing as dramatic as a supercontinent breaking apart precipitated the end of the Jurassic period, says Henderson, but something definitely happened.

“There is a change in the fossil record,” he says. “Even in the early days of geology in the 19th century, people recognized there was a break between Jurassic and Cretaceous faunas. It’s significant that in the northern hemisphere all the giant sauropods vanished, so things like diplodocus, brachiosaurus and brontosaurus.

“They survived on Gondwana,” says Henderson. “Things like titanosaurs in India, South America and Africa. But once their prey was gone, the giant predators in the north like allosaurus vanished as well.”

Scientists aren’t sure of the cause, although sea levels dropped during the late Jurassic. That would have destroyed a lot of prime marine habitat, while also reshaping ocean circulation patterns and, again, destabilizing terrestrial climates and plant and animal habitat.

And just like that (give or take a few million years), the Jurassic was history.

“Being biased toward dinosaurs, I think the Jurassic was a strange time,” says Henderson. “The average dinosaur was 10 times bigger than the largest animals today. Moving around, they would’ve just flattened the vegetation. But with Laurasia and Gondwana, there was a huge amount of land. Sauropods could grow big, and the landscape would support a population that wouldn’t go extinct.”

Jurassic oceans were much scarier than our oceans too, says Henderson.

“Apart from the Australian saltwater crocodile, we have no giant predatory marine reptiles. But in the Jurassic, there were animals like plesiosaurs filling the ocean. Most had substantial teeth, and were eating fish and squid. Pliosaurs had very large teeth, and they were clearly eating other marine reptiles. We have nothing like that now.” 

Sidebar

Critter Cornucopia

Giant-size dinosaurs may have dominated Jurassic Earth but other animals were around. Some even got their start during the Jurassic. But because they typically had smaller, more delicate bodies, they’re not easy for paleontologists to study, says the Royal Tyrrell’s Donald Henderson.

“If the animal isn’t eaten whole, their bodies tend to scatter and break apart,” he says. “But there are places like Solnhofen quarries in Germany where fine-grained limey mud settled in quiet, still water, and things were getting washed off land in storms and would sink to the bottom and be preserved.

“That deposit is one of our best windows into things like the archaeopteryx, which is the only bird known during the Jurassic, and small lizards,” he says. “No snakes yet, they don’t appear until the Cretaceous. But things like frogs, salamanders and turtles are there.”

A group that would eventually become mammals (cynodonts) was around during the Triassic, but true mammals didn’t appear until the early Jurassic, says Henderson.

“They’re mice and squirrel size,” he says. “Most are known from teeth and bits of jaw. They would have been nocturnal, maybe arboreal, or living underground, as all the daylight, large-bodied niches were filled by plant and meat-eating dinosaurs.

“Mammals were waiting in the wings,” says Henderson. “Once the stage was cleared with the end-Cretaceous extinction, mammals, within 10 million years, attained larger body sizes and filled all the vacant niches.”