Reconstructing Extinct Animals
How do we know what dinosaurs and other extinct organisms looked like? The animals and plants in the picture are carefully imagined reconstructions. The dromaeosaurs, for example, are shown standing on their hind legs, with their tails rigidly extended. Their hands are turned palms-in, and the second toe of each foot is tipped with an enormous claw. Fine feathers cover their bodies, while larger feathers project from their limbs. How much science backs up these reconstructions? In this section you can learn how scientists and paleo-artists interpret fossil evidence to create accurate images of dinosaurs.
We'll illustrate the steps using a reconstruction by paleoartist Gregory S. Paul of a giant sauropod related to Brachiosaurus.
Identify all the bones and put them together in a realistic pose.
Sometimes scientists are fortunate enough to be able to base their reconstructions on complete skeletons, but most excavated skeletons are missing pieces. The missing bones might have been destroyed by predators or scavengers as they fed on the animal, dissolved in acidic water, fractured under heavy sediments after burial, or broken while eroding out of the rock. How do scientists compensate for the missing bones? Fortunately, individuals of the same species, as well as those of closely related species, tend to be similar. This allows scientists to combine information from different partial skeletons in order to undertand how a complete skeleton would have looked.
Once all the bones are known, scientists arrange them in anatomically correct, lifelike positions. How do they judge what is lifelike for an animal no one has ever seen alive? Detailed studies of anatomy show that living animals with similarly constructed bones and joints hold their bodies similarly, so scientists model the stance of extinct animals on similar or related modern animals. This is reasonable because gravity would have constrained the stances, or postures, of extinct vertebrates just as it does for living animals. But bones alone do not tell the whole story. For example, cartilage discs between the vertebrae in an animal's backbone do not fossilize, but they do contribute to the animal's body length and range of motion. This creates uncertainty, and that means there always will be room for new ideas and debate about dinosaur stance.
Flesh it out with muscles.
Adding muscles is the next step in fleshing out a dinosaur skeleton. Fossil bones often contain muscle attachment scars that provide evidence about muscle location and size. But to know how to interpret these clues, scientists must first study similar features on the bones of modern animals. Because they observe that the massive muscles of large animals, such as elephants, leave larger muscle attachment scars than do the muscles of more lightly built animals, scientists and artists "add" more muscle to fossil bones with large muscle scars than to fossils that are more lightly scarred. It may help to estimate an animal's total body weight when doing a reconstruction. This is done by measuring skeletal features that correlate with weight in modern species, such as the diameter of the spinal canal in the vertebrae or the circumference of (distance around) the limb bones.
Give it some clothes to wear: add skin, feathers and armor (if needed), and color.
Finally, the skin is added, along with armor or feathers if the species is known to have them, and the animal is given color. Scientists and artists make use of several types of fossil evidence when deciding how to "clothe" dinosaurs in their reconstructions.
Rarely, the sediments near a fossilized skeleton retain impressions of the animal's skin. Such impressions formed if the animal was buried in fine sediments that hardened quickly, before the flesh rotted away. Impressions provide evidence of skin texture (smooth or scaly) over different parts of the body.
Some dinosaurs, such as ankylosaurs, are famous for their armor. Hard, bony plates, spines, and knobs grew embedded in their skin. The bones of the armor (called osteoderms) fossilized readily. When they are found in association with a well-articulated skeleton, they give a very good sense of how the armor was arranged over the body.
Exceptional theropod fossils from Liaoning, in northeastern China, show that many species of predatory dinosaurs were covered in feathers. The bodies of many species were covered with hair-like or downy feathers, while other species had long, pinnate feathers on their arms and tails, like birds. Few other fossil localites offer the exquisite preservation seen at Liaoning, but dinosaur fossils collected elsewhere do, sometimes, provide indirect evidence of feathers. Quill knobs are structures that anchor large feathers directly to the wing bones of modern birds. When they are found in the arm bones of dinosaurs, scientists infer that those dinosaurs had feathers.
Recently, an exquisitely preserved fossil theropod called Sinosauropteryx (SIGH-no-sore-OP-tair-icks) was found at Liaoning. Its feathers contain the fossilized remains of melanosomes, the pigment-making organelles that color skin, hair and feathers in modern animals. Researchers studied the pattern of these melanosomes and concluded that this little predator had an orange-and-brown striped tail!
The color of dinosaur skin remains a mystery. Artists may choose to use the colors of living animals as their palette when they depict dinosaurs, or they may let their imaginations run wild.
Meet our Paleoartist
Mary Parrish is a paleoartist. Her job is to create images that reflect how scientists think extinct organisms looked and behaved, and what their environments were like. Read an interview with Mary about the scientist/artist collaboration that led to this image of life in a Maryland wetland during the Cretaceous.
Find out more about Paleo Art
Learn about other Smithsonian scientist/artist collaborations by visiting a website highlighting Mary Parrish's reconstruction of a Carboniferous swamp, and John Gurche's early human reconstructions for the David H. Koch Hall of Human Origins.
For detailed information about illustration techniques, visit Mary Parrish's Paleo Art web pages.
A book that takes a detailed look at other artist/scientist collaborations is: The Artist and the Scientists Bringing Prehistory to Life, by Peter Trusler, Patricia Vickers-Rich and Thomas H. Rich. Cambridge University Press, September 20, 2010.
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