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