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Five Ways the World of the Dinosaurs Looked Different From Ours, Beyond the Presence of the ‘Terrible Lizards’
Earth has changed dramatically since the Age of Dinosaurs, from its climate to geography and animal life
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Imagine waking up in another time. A time of incredible dinosaurs.
From the pages of 19th-century novels to the screens playing summer blockbusters, countless stories have entertained the scenario. They almost always envision the great reptiles within thick and humid jungles, where tiny mammals shriek and scurry away from sharp-toothed shadows.
But the forests and swamps where most dinosaurs roamed didn’t resemble modern habitats. And the mammals of the time were not all so meek. Between the Triassic origin of the dinosaurs more than 235 million years ago and the cataclysmic asteroid strike 66 million years ago that left beaked birds as the only dinosaurs remaining, the Earth we now reside on was very different.
Were you to travel back to the time of Tyrannosaurus rex, Apatosaurus or even the earliest dinosaurs, you would be able to tell you’d awoken in another era without ever seeing a “terrible lizard.” Here are five ways—beyond the dinosaurs’ presence—that the Earth in their heyday was different from the one we know today.
Strange forests
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When the earliest dinosaurs began to step onto the Triassic scene, there were no flowering plants. Earth had no palm trees, grasses or citrus fruits. Many of the most numerous plants were larger and more varied relatives of those still around us today, such as ginkgo trees and horsetails. These grew alongside now-extinct lineages, like bennettitales—spiky relatives of cycads that sprouted broad fronds and were likely some of the first plants to be pollinated by animals.
For millions of years, through the Triassic and the Jurassic that followed, large dinosaurs kept such forests open and sunlit down to their trunks by feeding and trampling on plants. A sunny stand of conifers flanked by large horsetails and cycads sprouting up in an understory dotted by ferns was often the shape of a dinosaur-tended habitat.
It probably wasn’t until during the early Cretaceous, about 125 million years ago, that flowering plants as we know them today began to become more common. Some were wispy aquatic plants; others were relatives of today’s magnolias and so full of seeds that toothy birds foraged among their leaves. By 75 million years ago, palms grew alongside leafy flowering plants dotted with large fruit. But it was only after the big asteroid strike that more modern forests of close-growing, canopy-forming trees began to pop up, creating thick habitats where our primate ancestors evolved some of the key traits we still possess.
A global hothouse
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Our modern world can be a hot one, but the dinosaurs’ world was often hotter still, with sweltering stretches when the poles lacked ice and sea levels rose to the point of splitting continents in two.
The entire span of the Mesozoic—the Age of Dinosaurs, from Triassic to Cretaceous—was a very long time, nearly three times as long as the post-asteroid impact history of the planet. Earth’s climate didn’t maintain a constant temperature throughout that era: It swung between relatively warmer and cooler climates that had major effects on habitats.
Key context: When was the Age of Dinosaurs?
The Mesozoic era spanned between 66 million and 252 million years ago, and it was broken into three distinct periods.
- Cretaceous: 66 million to 145 million years ago
- Jurassic: 145 million to 201 million years ago
- Triassic: 201 million to 252 million years ago
The Triassic started off hot. The geological period followed Earth’s biggest mass extinction, during which volcanic eruptions in what’s now Siberia dumped incredible amounts of carbon dioxide and methane into the atmosphere, leading to rampant warming and an average global temperature of about 89 degrees Fahrenheit. (Today, the global average temperature is about 59 degrees Fahrenheit.)
Although temperatures fell after the early Triassic spike, the world remained warm for the rest of the Mesozoic. Although average global temperatures wobbled some, in the warmest times, what would have otherwise been polar ice was instead heated seawater, further altering rain patterns and the shape of ancient coasts. Dinosaurs lived in a seemingly endless global summer.
Continental shuffle
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Perhaps the most striking illustration of how different the Earth of the dinosaurs’ time was from our own would have been hard to perceive from the ground. It would have best been seen from space—the contrast only truly visible on a planetary scale.
When the first dinosaurs were stepping through ferns and cycads, most of Earth’s landmass was pushed together into a supercontinent called Pangaea. Due to the hot global temperatures, the most habitable regions were around the edges of the land, since the middle portion received little rain as the Triassic got going.
But Pangaea didn’t stay intact. Plate tectonics began to break it apart, shifting large chunks of the continent away from each other. Around 170 million years ago, in the middle of the Jurassic, what’s now Eurasia was separated from the other landmasses by a yawning gap of ocean, and smaller but spreading spans of sea divided North America from South America and Africa, which were attached to each other and close to ancient Australia and Antarctica.
The loosely connected northern continents, collectively known as Laurasia, became separated from the southern continents, or Gondwana, throughout the Jurassic. By the end of the Cretaceous, ocean was increasingly splashing between South America and Africa, with North America and Eurasia only intermittently connected by a land bridge in the north stretch of the prehistoric Pacific. Wherever you are on Earth right now, the location was once someplace very different.
Shifting seas
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Alongside these ever-changing coasts, the Mesozoic oceans were shifting, too, filled with coil-shelled ammonites, fishlike ichthyosaurs and other wonders. The warmth of these seas led them to rise and repeatedly spill over continents—places that are landlocked today used to be coastline.
The incursion of ancient seas is most visible from the Jurassic onward, as Pangaea continued to break up into component parts. The Sundance Sea spilled over North America in the mid- to late Jurassic, around 165 million years ago, only to recede and later be replaced by a long-lasting Western Interior Seaway that split the continent in two during the late Cretaceous. And life in those seas was unlike anything we know today.
Mesozoic waters were rife with unusual invertebrates. Among the most numerous and diverse were ammonites: many-armed cephalopods that lived in coiled shells. The largest of these plankton- and crustacean-eaters could grow shells that spanned eight feet in diameter. Cousins of sea stars called crinoids were incredibly common as well, looking almost like medieval maces on stalks. They might have grown in reefs that were made of enormous clams rather than coral.
But the marine reptiles were the most spectacular of all. Reptiles of many lineages began to evolve aquatic forms from the onset of the Triassic, and the fishlike ichthyosaurs were the first group to spin off whale-size species. The ichthyosaurs evolved alongside the long-necked plesiosaurs, which later included short-necked pliosaurs that preyed upon other marine reptiles, both groups thriving through the Jurassic and parts of the Cretaceous. Seagoing lizards called mosasaurs entered the water toward the end of the Mesozoic, but they evolved so rapidly that they became everything from blunt-toothed shell crunchers to open-water hunters. Sharks and sea turtles also swam the Mesozoic seas, but the ichthyosaurs, plesiosaurs and mosasaurs were unlike any creatures alive today.
Look out for mammals
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Mammals are among the most obvious animals in modern ecosystems—the past 66 million years is often called the Age of Mammals. But mammals thrived during the time of the dinosaurs, too, and those creatures were significantly different from our present-day relatives.
The earliest beasts that we would recognize as mammals are technically known as mammaliaformes, or “mammal-shaped animals,” and they evolved around the same time as the first dinosaurs. Most were small, just like most mammal species are today. Throughout the Mesozoic, they expanded into a variety of forms akin to modern otters, aardvarks, flying squirrels, badgers and more. Some may have even gotten to mountain lion size. But despite their familiar appearance, many of these early mammals reproduced and raised their young in different ways.
Some of the earliest mammaliaforms had many, many offspring, likely laying large clutches of eggs. Fossils of Kayentatherium, a mammaliaform from 185 million years ago, indicate that the creature could have litters of 38 babies at a time. The pattern suggests that these earlier mammals didn’t look after their offspring—instead, survival was a matter of numbers. But by 170 million years ago, some squirrel-like mammals were doing something different. Called multituberculates, these creatures were having smaller litters but putting in more effort—feeding their offspring milk and weaning them.
But many Mesozoic mammals were likely laying eggs or having tiny babies that needed more care out of the womb, like modern marsupials such as the kangaroo. Placental mammals like humans, which gestate their offspring to an advanced stage of development, didn’t appear until late in the Cretaceous and only became more prominent after the mass extinction of 66 million years ago. The most abundant and widespread Mesozoic mammals were the more archaic mammaliaforms and relatives of today’s pouched marsupials.
If you were in a strange forest on an unfamiliar coast and saw what at first appeared to be a squirrel but had tiny, close-eyed babies peeking out of a pouch, that’s all you’d need to know that you were back in the Age of Dinosaurs.
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