| Of all the life-forms now extinct, dinosaurs have | | | | feet [8 m] in length. Not unlike the African rhinoceros, |
| perhaps most stimulated the imagination of humans. | | | | these armored "tanks" featured a large skull |
| Dinosaurs are often imagined as having been huge | | | | extension forming a characteristic neck shield. A |
| and terrifying. When the name was first coined from | | | | three-horned version, triceratops, was common in the |
| the Greek words meaning "terrible lizard," they were | | | | dinosaur world. The two horns over the eyes grew |
| thought of as being fearfully large because the then | | | | up to three feet [0.9 m] long. Numerous fossils of |
| known dinosaur fossils were large. | | | | triceratops have been recovered from the Red Deer |
| Some types of dinosaurs were gigantic and did look | | | | River valley in Alberta. |
| fearsome, likely weighing more than ten times as | | | | The Saurischians-Dinosaur Giants |
| much as a large African elephant. However, over the | | | | Another general class of dinosaurs is known as |
| decades, paleontologists have unearthed bones of | | | | saurischians ("lizard hipped"), having hip structures like |
| many smaller dinosaurs. Some are the size of a | | | | those of lizards, though, again, much larger. They fit |
| donkey, and some are not much larger than a | | | | the usual concept of dinosaurs: huge and fearsome. |
| chicken! Let's take a look at some of these | | | | Among these were the apatosaurus (previously called |
| fascinating ancient reptiles. | | | | brontosaurus), a plant-eating dinosaur that walked on |
| Reptiles That Fly | | | | all four legs. It reached lengths of 70 feet [21 m] and |
| One intriguing type of ancient reptile was the | | | | weighed an estimated 30 tons. These dinosaurs have |
| pterosaur ("winged lizard"), which includes the | | | | been unearthed in North America and Europe. |
| pterodactyl ("winged finger"). But these were not | | | | The equally gigantic diplodocus was more snakelike, |
| dinosaurs, nor were they birds. They were flying | | | | with a long neck and tail but having legs. It is the |
| reptiles and are classified with other reptiles such as | | | | longest dinosaur known, stretching out some 90 feet |
| dinosaurs and crocodiles. Some of them had | | | | [27 m], though weighing somewhat less than the |
| wingspans of 25 feet [8 m]. One discovered in Texas | | | | apatosaurus. Uncovered in North America, the |
| in 1975 indicates that some had wingspans of more | | | | diplodocus had nostrils on top of its head, allowing it |
| than 50 feet [15 m]. These were perhaps the largest | | | | to submerge its head almost totally. |
| animals ever to fly. | | | | Then there is the brachiosaurus. A skeleton |
| While pterosaurs had the teeth, skull, pelvis, and hind | | | | discovered in Tanzania reached a length of 70 feet |
| feet of a reptile, they in no way resembled the | | | | [21 m]. It is estimated that some weighed more than |
| reptilian dinosaurs. And while they appeared to be a | | | | 85 tons. They stood 40 feet [12 m] tall, with a body |
| bird with stiff aerodynamic wings, they were much | | | | that sloped downward toward the tail, giraffelike. |
| different. Like birds, the pterosaurs had hollow bones | | | | In 1985 fossilized vertebrae of unusual size were |
| and few flexible joints in wings and ankles. However, | | | | unearthed in New Mexico, U.S.A. The curator of the |
| a bird's wings use feathers rather than a membrane | | | | New Mexico Museum of Natural History named it |
| as was the case with the pterosaurs. And the fourth | | | | seismosaurus. The animal was estimated to be about |
| finger of the pterosaur forelimb extended to support | | | | a hundred feet [30 m] in length and to tip the scales |
| the wing membrane. In the bird the second finger is | | | | at perhaps a hundred tons! |
| the principal support of the wing. | | | | The fierce-looking tyrannosaurus rex ("tyrant-lizard |
| The Ornithischians | | | | king") was about 10 feet [3 m] high at the hips. |
| The ornithischians ("bird hipped") were one of two | | | | When standing, it could measure some 20 feet [6 m] |
| general classes of dinosaurs as determined by the | | | | tall. It was about 40 feet [12 m] long. Its head was |
| structure of their hips. Those in this category had a | | | | up to four feet [1.2 m] in length, and its large mouth |
| hip structure similar to that of a bird but, of course, | | | | was equipped with many six-inch [15 cm] conelike |
| vastly larger. Some were small in overall size, others | | | | teeth. The hind legs were elephantine, while the front |
| huge. The iguanodon reached lengths of 30 feet [9 | | | | legs were very small. A huge lizardlike tail brought up |
| m]. Skeletons of several types of hadrosaurs indicate | | | | the rear. Rather than walking upright, it is now |
| a duckbill upper and lower jaw, with numerous teeth. | | | | concluded that the tyrannosaurs held their bodies |
| Hadrosaurs were apparently bipedal, walking or | | | | horizontal, balancing their body's weight with their long |
| running on two legs. Some of them reached lengths | | | | tail. |
| of 33 feet [10 m]. | | | | A Changing Scene |
| The stegosaurs were a group of the ornithischians | | | | That dinosaurs existed abundantly throughout the |
| that had large bony blades mounted in a pattern | | | | earth, in an ancient landscape long ago vanished, is |
| down their back. They walked on all four legs and | | | | obvious from the fossil record. But these amazing |
| were about 20 feet [6 m] long, and 8 feet [2.4 m] | | | | creatures, along with countless other animal and plant |
| high at the hips. More recently, it has been thought | | | | kinds, passed out of existence. As to just when |
| that the bony back plates served not just as a | | | | these things took place, paleontologist D. A. Russell |
| protection but as part of a cooling system for their | | | | states: "Unfortunately, existing methods for |
| body. Hind legs were heavy and elephantine, while | | | | measuring the duration of events that happened so |
| front legs were of smaller size, causing the small | | | | long ago are relatively imprecise." |
| head to be low to the ground. The tail had long, bony | | | | What happened to the dinosaurs? What does their |
| spikes radiating from the end. | | | | sudden appearance and apparently sudden extinction |
| A final group of ornithischians-widespread throughout | | | | mean? Do the dinosaurs bring into question some |
| the earth-was that of the ceratopsians, or horned | | | | basic principles of Darwinian evolution? We will explore |
| dinosaurs. They ranged from 6 feet [1.8 m] to 25 | | | | those questions in the following article. |