Why Dinosaurs No Longer Drag Their Tails

Why Dinosaurs No Longer Drag Their Tails
AP Photo/Francois Mori

The Mesozoic era, which began more than 250 million years ago, is probably as close as we will get to an alien living world—a world profoundly different from the biosphere in which humans evolved and now live. Dominating that world were, of course, the dinosaurs. These marvelous animals filled thousands of niches in nature and ranged in size from creatures smaller than a chicken to 70-ton monsters more than 120 feet from nose to tail tip, the largest beings to have ever walked the earth.

Until recent decades, we were able to perceive such a world only dimly, partly because we lacked the tools with which to explore it. Beyond what fossils had obviously verified, most of what we thought we knew about dinosaurs was really speculation, and, it turns out, much of it was wrong. In “Dinosaurs Rediscovered,” Michael J. Benton, a professor at the University of Bristol, takes us through what he calls a “scientific revolution” in his field of paleontology. It is a fascinating story, and Mr. Benton tells it both expertly and entertainingly.

It was the Victorians who first understood that the ancient earth was very different from the modern one—the word “dinosaur” was coined only in 1842. But they perceived the Mesozoic's creatures as great lumbering beasts that went through life dragging their tails behind them and finally died out from sheer stupidity, out-competed by mammals—an image that persisted, with some alteration, for more than a century.

Since about 1970, however, our understanding of dinosaurs has changed dramatically. New, rich fossils beds have been found in China, Argentina and North Africa, inaugurating a golden age of discovery and revealing animals of extraordinary range and diversity. There is the Yi qi, for instance, a small flying dinosaur whose fossil remains were found in China: It had both feathers and membranous wings, like a bat. In Morocco, fossils were found for the Spinosaurus, a creature about as big as a T. rex; but it was a semi-aquatic fish eater rather than a land animal. Such recent fossil discoveries, as well as older ones, have been subjected to new techniques of study—digital imaging, electron microscopes, CT scans—bringing dinosaurs to vivid life, at least in the human imagination.

Mr. Benton begins with the work of his own research group in 2010. Thanks to a refined understanding of biomechanics, it had become possible to estimate the shape of various dinosaurs. But what color were they? Dinosaurs had been traditionally depicted as gray or brown. But many living reptiles are brightly colored, so why shouldn't dinosaurs be? And some dinosaurs had feathers like their avian descendants, again suggesting a colorful presentation.

Eventually a scanning electron microscope detected so-called melanosomes in the fossilized feathers of a recently discovered dinosaur named Sinosauropteryx. (It was only 3 feet long and would have made an excellent pet for the Flintstone family.) Melanosomes are specialized parts of the cells for hair and feathers; differently shaped melanosomes produce different colors. Mr. Benton and his co-researchers determined that the Sinosauropteryx was orange, with an orange-and-white striped tail.

Well before advances in the understanding of dinosaur color, other researchers—led by Robert Bakker, both a paleontologist and a gifted artist—had revised the image of dinosaurs as tail-dragging hulks. Basing his drawings on the latest scientific evidence, Mr. Bakker portrayed theropods as dynamic and active creatures, their long tails balancing their bodies on the pivot of their hips. The menacing, steely-eyed Velociraptors in “Jurassic Park” convey this basic body architecture (though the movie's Velociraptors were in fact modeled on a different, larger dinosaur, the Deinonychus).

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