Dinosaur Revolution


The last thirty or so years have seen a tremendous change in the way we look at dinosaurs. We've been fascinated by these creatures ever since Cuvier reconstructed the first of them back around the turn of the 19th century. For more than a century, remains of dinosaurs were actively and enthusiastically pursued. This chase created one of the classic rivalries in the history of science, as Edward Drinker Cope and O. C. Marsh competed to see who could find and get credit for naming the most and the largest.

However, relatively early in the 20th century, this pursuit faded. Those who were interested in dinosaurs pretty much thought that they had them figured out. Dinosaurs were reptiles; they were big, slow moving, sluggish, stupid, and cold blooded. Like most reptiles, they lived without family responsibility and without social structure. Oh yes — they were also obviously unsuccessful. After all, they were extinct.

This whole picture began to crumble in 1964 when paleontologist John Ostrum discovered a new kind of dinosaur.

Deinonychus

He named his creature Deinonychus, and its characteristics contradicted several of these comfortable notions about dinosaurs' style.

For one thing, it wasn't all that big — a bit bigger than an ostrich. And it had more in common with an ostrich than size. The skeletal structure of Deinonychus is obviously designed, like the ostrich's, for running. Then there was that thing on the hind feet — the thing for which Ostrum named his dinosaur. Deinonychus means "terrible claw."

Foot of Deinonychus

One of the toes on the back feet of this dinosaur is reflexed — bent backward to lie along the shin — and equipped with a truly formidable claw.

This claw is pretty obviously an offensive weapon. Combining these anatomical features with some other aspects of this dinosaur, Ostrum came to the conclusion that Deinonychus was anything but slow and sluggish. In fact, he was built for an active, high energy life style. That's another problem — that kind of life style isn't consistent with cold bloodedness. Then there's his brain, which was apparently significantly larger than would be expected for a reptile of his size.

If you are having trouble visualizing Deinonychus from this description, think about the Velociraptor from the movie Jurassic Park. That dinosaur was actually a Deinonychus, though it was a couple of feet too long. The real Velociraptor is similar, though even smaller than Deinonychus.

The discovery of Deinonychus prompted paleontologists to take another look at all of the things that they "knew" about dinosaurs. Since this discovery, many of the features listed above have been shown to be partially or completely untrue. For instance, there is a lot of evidence that many kinds of dinosaurs did actually have group behaviors at least superficially similar to the herd behavior of some mammals. And a lot of new information has surfaced which shows us that at least some kinds of dinosaurs cared for their nests and for the young dinosaurs that hatched from the eggs in those nests. A lot of effort has been expended trying to really determine whether dinosaurs were cold blooded like reptiles, or warm blooded like birds (the dinosaurs' descendants). The question is far from settled — metabolism doesn't fossilize. However, there are strong indications that at least some dinosaurs were completely or partially warm blooded. It is hard to imagine a creature like Deinonychus being cold blooded. And if dinosaurs were actually warm blooded, can we continue to classify them as reptiles, since cold bloodedness is a defining characteristic of the Class Reptilia?

Then there is the question of success. Accusing dinosaurs of a lack of success is actually pretty funny. For well over 100 million years, dinosaurs occupied every terrestrial niche available for a creature bigger than a chicken. This is a record of overwhelming success. Mammals don't even come close to competing. They've been the predominant terrestrial vertebrate group for only 65 million years, and have never enjoyed the overwhelming dominance that dinosaurs had. Had it not been for whatever triggered the Cretaceous extinction 65 million years ago, dinosaurs might very will still be in charge, and enjoying the occasional small, nocturnal mammal as an hors d'ouvres.


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Updated 25 September 2004