Note to Tyrannosaurus rex: Avoid the water

A rare look at the monsters of the primordial seas

In "Sea Dragons" Richard Ellis gives us the first detailed look in nearly a century at the fiercest predators in the prehistoric oceans. Ellis is uniquely qualified to meet this huge task: A research associate at the American Museum of Natural History in New York, he is also an artist who draws his subjects as well as an accomplished author of books on the oceans and their inhabitants throughout history.

He admits that information about these sea beasts is sometimes skimpy, merely a few bone fragments in some cases. But he describes how paleontologists use comparative anatomy, which looks at characteristics of known sea creatures, to identify unknown species. As with the dinosaurs, scientists can piece together what the entire creature looked like and make educated deductions about their eating habits, mating practices, and methods of moving through the seas.

Although the book's tone is scientific, it's written in language accessible to the lay reader, and it's clearly a must read for any dinosaur aficionado.

Ellis's descriptions and rich illustrations spark curiosity, letting the reader realize, for instance, that the great white shark in "Jaws" was basically a wannabe menace. Carcharodon megalodon, a giant predator that resembled today's great white shark, was three times longer, an estimated 60 feet. Its teeth were six-inches long, three times as long as those of the great white.

Throughout the book Ellis brings up various theories about extinction. Some scientists, he notes, believe a massive asteroid that hit the Earth about 65 million years ago may have led to the extinction of the dinosaurs. Others think that climate change, large volcanic eruptions, and elimination of food sources were partly responsible. A more recent theory is that today's living birds actually are descended from terrestrial, feathered dinosaurs. This, writes Ellis, means that dinosaurs are not extinct at all.

As for the marine reptiles, Ellis says it is hard to imagine why they did not endure, as fossil evidence suggests they were numerous, efficient, and diversified. Extinctions of animals can be caused by a combination of factors that work together but remain little understood. They include global change as continents slid about, mountains were pushed up, and oceans cooled, warmed, dried up, or were formed once again. Ellis says the watery climate may have changed in such a way that only the warm-blooded mammals could survive. But since little is known about the primary prey of the large marine reptiles, the cause of their extinction remains a mystery.

The only extinctions we truly understand, Ellis concludes, are the ones we ourselves engineered, such as the dodo, passenger pigeon, and Tasmanian wolf.

Lori Valigra is a science writer in Cambridge, Mass.

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