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A Theory That Doesn't Fly

Scipionyx
Image: JOHN A. RUBEN

Lately, dinosaurs have gotten a whole new image. In the past few years, a number of paleontologists have reported skeletonal evidence that saurians were warm blooded, nurturing, and the probable ancestors of modern birds. But that cuddly theory doesn't fly with vertebrate paleobiologist John A. Ruben of Oregon State University. With a few bones of his own, Ruben contends that dinosaurs are more kin to a crocodile than a cockatiel.

Ruben's latest piece of evidence is this photograph of a baby theropod known as Scipionyx. The fossil, which was discovered near Naples, Italy in 1983, is unusual in that it contains remarkably well preserved internal organs. When Ruben and his colleague Willem J. Hillenius of the College of Charleston, in South Carolina, illuminated Scipionyx with ultraviolet light the fossilized tissues fluoresced in various colors because they had replaced by minerals at differing rates. The spectacular result was as close as a paleontologist will ever get to examining a prepared 110-million year old specimen on a dissecting table.

In a paper published in the January 22 issue of Science, Ruben and his colleagues argue that Scipionyx was cold blooded and had breathing apparatus much different from that of birds but was capable of moving at great speed. The investigators based their conclusion on the position of the colon (box, center) and the liver (box, center), which are similar to the modern crocodile.

The colon in birds runs through the center of the abdominal cavity while that of Scipionyx--and crocodiles--is located high up against the spine. The location of the liver also suggests another feature of crocodilians, a specialized breathing mechanism known as a hepatic piston. Crocs have a non-muscular diaphragm powered by muscles which attach to the liver and the pubic bones of the hip. Muscles pull the large liver backwards to inflate the lungs for bursts of activity. That the animal was a fast runner is supported by the strong bands of well developed muscles that run from the pelvis to the upper legs (box, left).

Ruben's recent publication is consistent with the case he presented in a November 1997 paper, also in Science. in which he contended that the skeletonal structures in the theropod dinosaurs were not consistent with bird-like lungs. In earlier findings, Ruben argued that CAT scans of dinosaur nasal structure clearly suggested that dinosaurs were not warm-blooded, since they lacked the nasal "turbinates" that warm-blooded animals use to prevent excess heat and water loss while breathing. The picture of Scipionyx is unlikely to put the debate to rest. But it is the first time paleontologists have gotten a clear look at the internal anatomy of a dinosaur. And, Ruben's evidence is, after all, cast in stone.

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