The 10 Most Important Facts About Dinosaurs

Digital illustration of the dinosaur, Irritator.
An artist's rendering of the Irritator, a close relative of Spinosaurus. Sergey Krasovskiy / Getty Images

It's common knowledge that dinosaurs were really big, some of them had feathers, and they all went extinct 65 million years ago after a giant meteor hit the Earth. But what don't you know? Here is a quick and easy overview of the most important highlights of what was happening in the Mesozoic Era.

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Dinosaurs Weren't the First Reptiles to Rule the Earth

Digital illustration of the dinosaur, Arctognathus.

Dmitry Bogdanov / Wikimedia Commons / CC BY 3.0

The first dinosaurs evolved during the middle to late Triassic period—about 230 million years ago—in the part of the supercontinent of Pangea that now corresponds with South America. Before then, the dominant land reptiles were archosaurs (ruling lizards), therapsids (mammal-like reptiles), and pelycosaurs (typified by Dimetrodon). For 20 million or so years after dinosaurs evolved, the most fearsome reptiles on Earth were prehistoric crocodiles. It was only at the beginning of the Jurassic period, 200 million years ago, that dinosaurs truly began their rise to dominance.

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Dinosaurs Prospered for Over 150 Million Years

Digital illustration of the dinosaur, Acrocanthosaurus

DEA Picture Library / Getty Images

With our 100-year-max life spans, humans aren't well adapted to understanding "deep time," as geologists call it. To put things in perspective: Modern humans have only existed for a few hundred thousand years, and human civilization only got started about 10,000 years ago, mere blinks of the eye by Jurassic time scales. Everyone talks about how dramatically (and irrevocably) the dinosaurs went extinct, but judging by the whopping 165 million years they managed to survive, they may have been the most successful vertebrate animals ever to colonize Earth.

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The Dinosaur Kingdom Comprised Two Main Branches

Digital illustration of the dinosaur, Saurolophus defending its nest.
Sergey Krasovskiy / Getty Images

You'd think it would be most logical to divide dinosaurs into herbivores (plant-eaters) and carnivores (meat-eaters), but paleontologists see things differently, distinguishing between saurischian ("lizard-hipped") and ornithischian ("bird-hipped") dinosaurs. Saurischian dinosaurs include both carnivorous theropods and herbivorous sauropods and prosauropods, while ornithischians account for the remainder of plant-eating dinosaurs, including hadrosaurs, ornithopods, and ceratopsians, among other dinosaur types. Oddly enough, birds evolved from "lizard-hipped," rather than "bird-hipped," dinosaurs.

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Dinosaurs (Almost Certainly) Evolved Into Birds

A digital illustration of the dinosaur, Archaeopteryx
Leonello Calvetti / Getty Images

Not every paleontologist is convinced—and there are some alternate (albeit not widely accepted) theories—but the bulk of the evidence points to modern birds having evolved from small, feathered, theropod dinosaurs during the Late Jurassic and Cretaceous periods. Bear in mind, though, that this evolutionary process may have happened more than once and that there were definitely some "dead ends" along the way (witness the tiny, feathered, four-winged Microraptor, which has left no living descendants). In fact, if you look at the tree of life cladistically—that is, according to shared characteristics and evolutionary relationships—it's completely appropriate to refer to modern birds as dinosaurs.

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Some Dinosaurs Were Warm-Blooded

A model of the Velociraptor.

Salvatore Rabito Alcón / Wikimedia Commons / CC BY 3.0

Modern reptiles like turtles and crocodiles are cold-blooded, or "ectothermic," meaning they need to rely on the external environment to maintain their internal body temperatures. Modern mammals and birds are warm-blooded, or "endothermic," possessing active, heat-producing metabolisms that maintain constant internal body temperature, no matter the external conditions. There's a solid case to be made that at least some meat-eating dinosaurs—and even a few ornithopods—must have been endothermic since it's hard to imagine such an active lifestyle being fueled by a cold-blooded metabolism. On the other hand, it's unlikely that giant dinosaurs like Argentinosaurus were warm-blooded since they would have cooked themselves from the inside out in a matter of hours.

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The Vast Majority of Dinosaurs Were Plant Eaters

A digital illustration of the dinosaur, Mamenchisaurus
Sergey Krasovskiy / Getty Images

Fierce carnivores like Tyrannosaurus rex and Giganotosaurus get all the press, but it's a fact of nature that the meat-eating "apex predators" of any given ecosystem are tiny in number compared to the plant-eating animals on which they feed (and which themselves subsist on the vast amounts of vegetation needed to sustain such large populations). By analogy with modern ecosystems in Africa and Asia, herbivorous hadrosaurs, ornithopods, and to a lesser extent sauropods, probably roamed the world's continents in vast herds, hunted by sparser packs of large-, small-, and medium-sized theropods.

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Not All Dinosaurs Were Equally Dumb

A digital illustration of the dinosaur, Troodon

DEA Picture Library / Getty Images

It's true that some plant-eating dinosaurs like the Stegosaurus had such tiny brains compared to the rest of their bodies that they were probably only a little smarter than a giant fern. But meat-eating dinosaurs large and small, ranging from Troodon to T. rex, possessed more respectable amounts of gray matter compared to their body size. These reptiles required better-than-average sight, smell, agility, and coordination to reliably hunt down prey. (Let's not get carried away, though—even the smartest dinosaurs were only on an intellectual par with modern ostriches.)

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Dinosaurs Lived at the Same Time as Mammals

A digital illustration of Megazostrodon

DEA Picture Library / Getty Images

Many people mistakenly believe that mammals "succeeded" the dinosaurs 65 million years ago, appearing everywhere, all at once, to occupy the ecological niches rendered vacant by the K-T extinction event. The fact is, though, that early mammals lived alongside sauropods, hadrosaurs, and tyrannosaurs (usually high up in trees, away from the heavy foot traffic) for most of the Mesozoic Era. In fact, they evolved at around the same time—during the late Triassic period—from a population of therapsid reptiles. Most of these early furballs were about the size of mice and shrews, but a few (like the dinosaur-eating Repenomamus) grew to respectable sizes of 50 pounds or so.

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Pterosaurs and Marine Reptiles Weren't Technically Dinosaurs

A digital illustration of the dinosaur, Mosasaur swimming.

Sergey Krasovskiy/Stocktrek Images / Getty Images

It may seem like nitpicking, but the word "dinosaur" applies only to land-dwelling reptiles possessing a specific hip and leg structure, among other anatomical characteristics. As large and impressive as some genera (such as Quetzalcoatlus and Liopleurodon) were, flying pterosaurs and swimming plesiosaurs (ichthyosaurs and mosasaurs) weren't dinosaurs at all—and some of them weren't even all that closely related to dinosaurs, save for the fact that they're also classified as reptiles. While we're on the subject, Dimetrodon—which is often described as a dinosaur—was actually an entirely different kind of reptile that flourished tens of millions of years before the first dinosaurs evolved.

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Dinosaurs Didn't All Go Extinct at the Same Time

Tyrannosaurs fleeing a hail of meteorites

When that meteor impacted the Yucatán Peninsula 65 million years ago, the result wasn't a huge fireball that instantly incinerated all of the dinosaurs on Earth, along with the pterosaurs, and marine reptiles. Rather, the process of extinction dragged on for hundreds, and possibly thousands, of years, as plunging global temperatures, lack of sunlight, and the resulting lack of vegetation profoundly altered the food chain from the bottom up. Some isolated dinosaur populations, sequestered in remote corners of the world, may have survived slightly longer than their brethren, but it's a sure fact that they are not alive today.

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Strauss, Bob. "The 10 Most Important Facts About Dinosaurs." ThoughtCo, Jul. 30, 2021, Strauss, Bob. (2021, July 30). The 10 Most Important Facts About Dinosaurs. Retrieved from Strauss, Bob. "The 10 Most Important Facts About Dinosaurs." ThoughtCo. (accessed June 5, 2023).