The first of a two-part series
Dinosaurs died out about 66 million years ago, yet they live on in our imagination. They populate books and toy shelves. They also star on the big screen in blockbuster movies like 1993’s Jurassic Park and this summer’s Jurassic World. Such efforts have made us all familiar with creatures like the fearsome Tyrannosaurus rex, the three-horned Triceratops and the long-necked Brachiosaurus.
But not all dinosaurs were immense beasts. Some were only the size of chickens. And not every prehistoric reptile was a dinosaur.
Dinosaurs are but one small group of reptiles. Ancient ecosystems also hosted the ancestors of today’s crocodiles, snakes, lizards and turtles. And the landscape teemed with many other types of reptiles that are now long gone. Some lived in the sea. Others took to the air and soared like birds. Some lived on land and, at first glance, resembled dinosaurs. But the detailed features of their fossils, or ancient remains, clearly show they were not dinos.
“In many cases, these animals played very important roles in their ecosystems,” says Thomas Holtz, Jr. He works at the University of Maryland in College Park. As a vertebrate paleontologist, he studies the fossils of creatures with backbones.
Many of these ancient non-dinos died out at the same time as dinosaurs. Others went extinct millions of years earlier. Scientists still aren’t sure why. Studying the fossil record can provide clues. It also can show which groups of ancient creatures are most closely related, when they first appeared and how they evolved — changed over time.
It’s all in the hips
For millions of years, dinosaurs dominated many of Earth’s ecosystems. The first dinos emerged in the fossil record about 235 million years ago. They disappeared some 169 million years later. Some scientists think a massive comet or asteroid struck Earth and wiped them out.
Some dinosaurs were big. Others were small. Some ate animals. Others dined solely on plants. Some ran on two legs; others walked on all fours. But all had at least one thing in common, notes Sterling Nesbitt. He’s a vertebrate paleontologist at Virginia Tech in Blacksburg. Every dinosaur had holes where its thighbones, or femurs, attached to the pelvis. “All dinosaurs had this open hip socket,” he says. “It’s not found in any other reptiles.” Simply put, reptiles lacking this hip structure were not dinosaurs.
Scientists look at traits like hip structure to distinguish species. Each species, whether living or long extinct, has its own special set of characteristics. Birds have feathers, and mammals have hair. Today’s reptiles have scales. Fossils suggest that most dinosaurs had scales too. So do fish (but their scales are different). The more traits that two species share, the more closely related they tend to be. “By looking at shared characteristics, you can tell what creatures are related,” says James Clark. He’s a vertebrate paleontologist at George Washington University in Washington, D.C.For living creatures, Clark notes, scientists often go beyond anatomy and consider similarities or differences in genetic material such as DNA. But for ancient animals, scientists typically have only fossils. Researchers can use those various characteristics to build a family tree. This method of mapping family trees is called cladistics (Klah-DISS-tiks).
Cladistics reveals that many different types of reptiles lived during ancient times. In fact, the Mesozoic Era, which lasted from 252 million to about 66 million years ago, is often referred to as “the Age of Reptiles.” Among animals during that lengthy era, reptiles dominated. But among them, dinosaurs were only one group.
Even if something looked and behaved like a dinosaur, it wasn’t a dinosaur unless it had the right hip structure. Consider a ferocious meat-eater just described by Nesbitt and his teammates in the November 4, 2014 Journal of Vertebrate Paleontology. The team named the creature Nundasuchus (NOON-dah-SOO-kuss). In the local Swahili language, nunda means “predator.” The suffix suchus is from a Greek word for “crocodile.”
Nundasuchus was probably about 2.75 meters (9 feet) long. Some of its teeth had edges that were serrated, like steak knives. But this ancient meat-eater was not a dinosaur. It didn’t have the right hip structure. And the reptile’s ankle bones were similar to those of animals in a different group of reptiles, called Pseudosuchia (SOO-doh-SOO-kee-ah). That name is a combination of Latin and Greek words that means “false crocodiles.”
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The researchers found the animal’s fossil bones in Tanzania, in southeastern Africa. Those bones had been entombed around 242 million years ago. They didn’t form a complete skeleton, but they did include bones, or bits of bones, from almost all parts of the animal. Those remains let the team measure hundreds of the creature’s anatomical details. Importantly, the scientists found a left rear leg that was very nearly complete. “I could tell this was a new species almost immediately,” Nesbitt says.
It would have belonged to a group of species that includes true crocodiles and their living and extinct relatives. It also includes other groups of ancient and now-extinct reptiles. One is called the rauisuchids (RAOW- ee-SOO-kidz). These meat-eaters, some of which reached lengths of 6 meters (20 feet), are often mistaken for dinosaurs because they look so similar. But their hips show they aren’t dinosaurs at all.
Up in the air!
Birds weren’t the first vertebrates to take to the skies. One group of reptiles beat them to it by a good 75 million years or more. Called pterosaurs (TAIR-oh-saurs), these creatures take their name from the Greek words for “wing lizard.”
Pterosaurs were close relatives of dinosaurs. Their hip structures were roughly similar. Pterosaurs and dinosaurs also are the only groups of reptiles that have one particular arrangement of bones in their ankles. “It’s very distinctive,” says Clark. Yet these similarities don’t mean that pterosaurs evolved from dinosaurs, he explains. It simply means that they both shared some common ancestor. So, on the reptile family tree, they were only cousins.The oldest known pterosaurs were well adapted for flying. Like birds, their bones were hollow and filled with air. That helped make their bodies light and easier to get off of the ground. But unlike birds, pterosaurs had no feathers. Instead, their wings were covered in thin membranes made of skin and other tissues. Those membranes stretched between their wings’ bones (which included a very long finger) and their bodies. Sometimes the rear edge of the wings stretched back and connected to a pterosaur’s ankles. (This past April, scientists reported finding Yi qi , a species of small dinosaur with a pterosaur-like wing membrane. But it’s not yet clear if that creature was truly able to flap and fly like birds and pterosaurs, the researchers say. Perhaps it could only glide.)
For the first 70 million years, pterosaurs remained pretty much the same size, says Roger Benson. He’s a vertebrate paleontologist at the University of Oxford in England. All pterosaur species during that time had an average wingspan of about 1.2 meters (4 feet). Then, starting about 150 million years ago, pterosaurs began enlarging. And that trend continued until the animals became extinct 66 million years ago. Near the end, the wings of various species spanned from 3 meters (10 feet) to 10 meters (33 feet) across. (For comparison, a U.S. Air Force F-16 fighter jet has a 10-meter wingspan.)
Two things drove that growth in average wingspan. Some huge species evolved. At the same time, most small pterosaur species vanished. This might be linked to the appearance of the first birds, researchers suggested in 2014 in Nature Communications. And here’s why: Birds and small pterosaurs probably dined on the same types of creatures. Early birds might have been more active or more agile than pterosaurs their size. So the flying reptiles might have lost out when competing with birds for a meal. In time, these small pterosaurs largely died out. Those that survived did so by evolving into such immense sizes that they no longer competed with birds.
Many people incorrectly call all flying reptiles “pterodactyls.” That name, which comes from the Greek words for “wing finger,” belongs to only one group of pterosaurs. They get their name from the long thin finger that supports the front edge of their wing, explains Clark. Typically, a pterosaur is considered a pterodactyl if the longest bone in its wing finger is eight times longer than its diameter.
That’s just weird
Dinosaurs are well known for their unusual appearance. Many had horns, spikes, plates or any of plenty of other odd features. Pterosaurs could look pretty weird too. Some early species had toothy jaws and long tails. Many later species had no teeth and almost no tail.
But one pterosaur might have looked much weirder than the rest. It lived about 120 million years ago in what is now northeastern China. Adults probably had a wingspan of about 1.5 meters (5 feet). In many ways, this flying reptile looked like other pterosaurs. But its fossils provide tantalizing clues that this species was special. The front portion of its lower jaw had a deep, thin, crescent-shaped keel of bone. Near the point where this semicircle joined the lower jaw, there was a peculiar hook-shaped projection.
Its fossils were first described in the journal Scientific Reports in 2014.
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No other pterosaur has this distinctive feature. In fact, its discoverers say, no other vertebrate, living or long extinct, has such a bony projection. Because of that, scientists aren’t quite sure what purpose this hook served. It may have been an anchor for soft tissue. (Unlike bones, soft tissues rarely get preserved as fossils.) Indeed, based on where the hook is located, the pterosaur might have had a pelican-like pouch beneath its lower jaw. This pouch could have held fish that the pterosaur scooped up as it swooped across the surfaces of lakes or rivers.
The scientists named the new species Ikrandraco avatar. “Draco” is the Latin word for dragon. The other two parts of the name come from the name of the movie Avatar and the fictional flying beasts, “ikran,” that were ridden by warriors in that film’s battles.
The lesson with this animal, as with many other ancient creatures, is that just because something outwardly resembled a dinosaur did not mean it was one.
Next: The ancient reptiles that ruled the seas
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anatomy The study of the organs and tissues of animals. Scientists who work in this field are known as anatomists.
asteroid A rocky object in orbit around the sun. Most orbit in a region that falls between the orbits of Mars and Jupiter. Astronomers refer to this region as the asteroid belt.
cladistics An approach to biological classification in which organisms are grouped together based on whether or not they share anatomical characteristics.
comet A celestial object consisting of a nucleus of ice and dust. When a comet passes near the sun, gas and dust vaporize off the comet’s surface, creating its trailing “tail.”
dinosaur A term that means terrible lizard. These ancient reptiles lived from about 250 million years ago to roughly 65 million years ago. All descended from egg-laying reptiles known as archosaurs. Their descendants eventually split into two lines. They are distinguished by their hips. The lizard-hipped line became saurichians, such as two-footed theropods like T. rex and the lumbering four-footed Apatosaurus (once known as brontosaurus). A second line of so-called bird-hipped, or ornithischian dinosaurs, led to a widely differing group of animals that included the stegosaurs and duckbilled dinosaurs.
DNA (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
doppelgänger A word from the German that means a look-alike — or double — of someone or some thing.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.
evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.
extinct An adjective that describes a species for which there are no living members.
femur In humans, the large bone in the upper leg. It is commonly known as the thighbone. In tetrapods (creatures with four limbs), it’s the large bone in the upper hind limbs.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
genus A group of closely related species. For example, the genus Canis — which is Latin for “dog” — includes all domestic breeds of dog and their closest wild relatives, including wolves, coyotes, jackals and dingoes.
keel A structural feature that runs along the bottom of a boat’s hull from front to back (stem to stern) and may almost look like a fin extending down into the water. The boat’s beams or flooring are usually attached to this.
Mesozoic Era An interval of geologic time from about 252 million to around 66 million years ago. Often called the Age of Reptiles, this era includes the Triassic, Jurassic and Cretaceous periods.
paleontologist A scientist who specializes in studying fossils, the remains of ancient organisms.
paleontology The branch of science concerned with ancient, fossilized animals and plants.
pelvis Bones that make up the hips, connecting the lower spine to leg bones. There is a gap in the middle of the pelvis that is larger in females than in males and can be used to tell the sexes apart.
predator (adjective: predatory) A creature that preys on other animals for most or all of its food.
projection Something feature that extends out (or projects) from the body of a structure.
pterosaur Any of various extinct flying reptiles of the order Pterosauria. These animals lived 245 million years ago to 65 million years ago. Although not true dinosaurs, they lived during the reign of dinosaurs. Among members of this order were the pterodactyls of the Jurassic and Cretaceous periods, which were characterized by wings consisting of a flap of skin supported by the very long fourth digit on each forelimb.
pterodactyl A group of pterosaurs that get their name from the long thin finger that supports the front edge of their wing. Typically, a pterosaur is considered a pterodactyl if the longest bone in its wing finger is eight times longer than its diameter.
reptile Cold-blooded vertebrate animals, whose skin is covered with scales or horny plates. Snakes, turtles, lizards and alligators are all reptiles.
serrated A description for a saw-like edge, usually found on knives meant to cut through tough meat.
trait A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
tyrannosaur A line of meat-eating dinosaurs that began during the late Jurassic Period, about 150 million years ago. These species persisted into the late Cretaceous Period, about 65 million years ago. The best known member of these species: the late Cretaceous’ Tyrannosaurus rex, a 12-meter (40 foot) long top predator of its time.
Tyrannosaurus rex A top-predator dinosaur that roamed Earth during the late Cretaceous period. Adults could be 12 meters (40 feet) long.
vertebra (plural vertebrae) One of the bones that make up the neck, spine and tail of vertebrates. Bones in the neck are called cervical vertebrae. Bones in the tail, for animals that have them, are called caudal vertebrae.
vertebrate The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes all fish, amphibians, reptiles, birds, and mammals.
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