Dinosaurs are nature’s celebrities. We love them. Many of us, in the near-ubiquitous “dinosaur phase” of our youth, quickly master names like Tyrannosaurus, Diplodocus, and—the challenge of any young fossil fan—Pachycephalosaurus by the time we start kindergarten. But dinosaurs are changing so fast that the monstrous creatures we imagine in our youth become strangers as scientific discovery continues to tweak what we know about them. This disjunction spurs myths and misunderstandings that persist for decades, and often obscure how wonderful dinosaurs truly were. Time to do a little pop culture housekeeping to clear out old assumptions.
1: Tyrannosaurus and Apatosaurus lived together
As a kid, I spent hours staging battles between my plastic Tyrannosaurus—king of the tyrant dinosaurs—and a stocky, long-necked Apatosaurus model. But the dinosaurs never would have met each other. Apatosaurus roamed western North America about 150 million years ago, over 80 million years before Tyrannosaurus evolved. In fact, a greater span of time separated Apatosaurus and Tyrannosaurus than separates us from that most famous of the carnivorous dinosaurs—a relatively scant 66 million years. But sandbox dinosaur fans, take heart. Even though Tyrannosaurus never ate Apatosaurus, the giant predator lived in the same Late Cretaceous habitats as Alamosaurus—a huge sauropod dinosaur found in the southwestern United States. Tyrannosaurus probably enjoyed sauropod steak, after all.
2: “Dinosaur” means anything ancient and reptilian
Even though the word is familiar, “dinosaur” is a technical term that applies to a specific group of animals that are united by a suite a shared characteristics and bound together by evolutionary history. Just because some prehistoric creature was big or had nasty teeth doesn’t automatically make it a dinosaur. The proof is in anatomical detail and the creature’s specific relationships. In the bigger evolutionary picture, dinosaurs were just one lineage within a group called archosaurs. This group also includes pterosaurs, crocodiles, and their closest living relatives, all of which split from each other by about 245 million years ago. Dinosaurs were a specific part of this archosaur radiation, distinct from other archosaurs and other forms of prehistoric reptiles. While they lived alongside dinosaurs, the flying pterosaurs and marine reptiles such as the long-necked plesiosaurs, fish-like ichthyosaurs, and swimming lizards called mosasaurs were not dinosaurs.
3: Big dinosaurs had butt brains
Some dinosaurs—such as the mighty sauropods and the armored Stegosaurus—had extra-large cavities in their hips. The wide spaces were associated with the neural canal, where the spinal cord passes, and so 19th century paleontologist Othniel Charles Marsh speculated that the space housed a “posterior braincase” that helped the dinosaurs coordinate their legs and tails.
But paleontologists now know that no dinosaur had a second brain. First, many different kinds of vertebrates have a slight expansion of the spinal cord in the vicinity of their limbs. This slight swelling of the nervous system helps regulate limb movement. But Stegosaurus and sauropods had even larger expansions that probably housed a strange feature called a glycogen body. This kind of tissue, seen in the hips of birds, might store energy-rich carbohydrates, although zoologists still aren’t entirely sure if this is the case. One thing is for sure, though—dinosaurs did not have brainy butts.
4: Tyrannosaurus arms were wimpy
Tyrannosaurus forelimbs look small compared to their bulky bodies and massive skulls, but the appendages were not as weak as they might appear. The arms of Tyrannosaurus were stout and heavily-muscled, so much so that the dinosaur could probably flex an excess of 430 pounds with each arm. No human bodybuilder can match that. And, if we’re going to tease any dinosaur for small arms, Carnotaurus is a more apt target. In the arms of this carnivore, the bones of the lower arm, wrist, and hand are compressed into a short skeletal stack attached to a flexible upper arm bone. If Carnotaurus wanted to attack another dinosaur with its arms, the predator’s forelimbs would have only been able to do ineffectual pinwheels.
5: Dinosaurs dragged their tails
You’d think that Jurassic Park and decades of fantastic paleoart would have killed this one, but apparently not. While generations of paleontologists reconstructed dinosaurs with limp, drooping tails, since the 1970s researchers have been more properly restored dinosaurs with spines held parallel to the ground and lifted tails. This evidence not only comes from osteology—including tail support structures such as strengthening ossified tendons in some dinosaurs—but also from trackways that fail to preserve the tail drags that would have been expected if the dinosaurs were walking in a Godzilla pose or had slack tails.
6: Dinosaurs were the terrors of small mammals
Our mammalian ancestors and cousins remained relatively small during the Mesozoic reign of the dinosaurs. This has often been taken as an indication that the Triassic, Jurassic, and Cretaceous landscapes were dangerous places for the small and fuzzy. But mammals ate dinosaurs, too. A specimen of Repenomamus—a 125 million year old mammal about the size of a badger—had baby dinosaurs preserved in its gut contents. No one knows whether the mammal scavenged the infants or actively raided a nest, but the sharp-toothed mammal was certainly capable of eating little dinosaurs. Other mammals chewed dinosaurs post mortem—some dinosaur bones show distinctive gnaw marks that could only have been created by small mammals.
7: Dinosaurs always lived in a humid, endless summer
The classic imagery of prehistoric dinosaurs features fantastic animals in dense jungles and murky swamps. Some dinosaurs inhabited environments like this, that’s true, but the whole diversity of dinosaurs actually occupied a diversity of habitats all over the globe for about 160 million years. There were even dinosaurs in the snow. Late Cretaceous sites in the High Arctic contain the remains of dinosaurs that lived in relatively cool habitats that would have been dark for much of the year, and, based on ancient climate reconstructions, which probably experienced snowfall. A fuzzy tyrannosaur striding through the snow is quite different than the sauropods lumbering through weed-choked wetlands that I grew up with.
8: Quirks of the ancient Earth made dinosaurs so big
Why were the biggest dinosaurs so much larger than any terrestrial creature alive today? There’s been no shortage of explanations, including the idea that gravity was different or there was more oxygen in the air. But gravity in the Mesozoic was the same as it is today, and, in fact, reconstructions of the ancient atmosphere indicates that the atmosphere’s oxygen content might have actually been slightly lower during the time of dinosaur giants. Instead, dinosaurs such as Supersaurus got so large because of two factors of their biology. Not only did sauropod and theropod dinosaurs have special air sacs that made their skeletons lighter without sacrificing strength, the fact that dinosaurs reproduce by laying clutches of small eggs allowed them to get around the reproductive constraints that prevent land-dwelling mammals from becoming larger.
9: All dinosaurs were big
The biggest dinosaurs are the ones that immediately fire our imagination. But not all dinosaurs were giants. Part of what made dinosaurs so successful is that they occupied a range of body sizes, from small to absolutely gigantic. Among the smallest dinosaurs were pigeon-sized forms such as the feathery, bird-like Anchiornis and the fluffy little theropod Scansoriopteryx. And, of course, babies of these diminutive dinosaurs would have been even smaller still.
10: Dinosaurs are dead
Dinosaurs are still with us. Even though the charismatic, non-avian forms all died out in a devastating mass extinction 66 million years ago, the avian lineage survived and persists to this day. Indeed, the dinosaur lineage known as “birds” evolved by 150 million years ago, and these feathery dinosaurs—from hummingbirds to ostriches to penguins—remind us of their lost relatives today.