"We need not marvel at extinction, "Charles Darwin wrote, but "if we must marvel, let it be at our presumption in imagining for a moment that we understand the many complex contingencies on which the existence of each species depends."

Roughly a century and a half after Darwin's observation, the general public still marvels at the most popular of bygone species, the dinosaurs, and at their extinction 65 million years ago. The most recent addition to the mounting stack of dinosaur-extinction books is The Mistaken Extinction by paleontologists Lowell Dingus and Timothy Rowe. Their approach is like a detective story. This design makes sense: There has been a murder (a mass murder, in fact), and the detectives are not only at the scene of the crime, they follow the case history of the victims.

The first part of this "three pipe problem," as Sherlock Holmes would say, is the murder. Supposedly using a "you can judge for yourself" approach, Dingus and Rowe examine much of the available evidence of the events leading up to the extinction of the dinosaurs 65 million years ago. These victims were not the only unlucky ones, however: Many of the global ecosystems of their time were also under stress. The authors review contributing factors - such as sea-level changes, massive volcanic emissions (especially on the Indian subcontinent), tectonic activity, and a meteor impact - that have lead to numerous theories explaining what happened way back then. Synthesizing these, as the authors do, gives one the impression that either a meteor or a massive volcanic release from India (which is now preserved as the Deccan traps) was the perpetrator. The former "perp" is heavily favored by the authors.

The book's either-or approach, though excellent in preserving clarity, is probably one of its noticeable flaws. Only near the end of the first section of the book, in a few short pages, is there any clear discussion about whether multiple factors conspired to cause the extinction. Yet as the authors admit, extinction is a complex array of problems and situations that includes and affects, at multiple levels, the constituents of the biological community - at times local, at rarer times, global. In real life, there is no black or white. The Deccan emissions did occur; they were not created by a hypothetical event. The consequences of such emissions must have produced devastating local and global effects and undoubtedly affected the biosphere to the detriment of many of the planet's inhabitants.

Dingus and Rowe review other suspects in the case of the dead dinosaurs. In North America, for example, the Western Interior Seaway, which longitudinally split the continent in half for most of the Cretaceous Period, dried up. The consequences of such a gradual event would have posed new problems and opportunities to the constituents of ecosystems in affected areas. And the authors outline the evidence that something - probably a large meteor - pierced our atmosphere, crashed into the Earth, and severely altered the environment by producing an enormous amount of fallout. Still, an important question remains: At what level do all possible global events interact, especially those that occurred 65 million years ago? No has yet been able to gauge an answer to that question, as Darwin forewarned long ago.

The second part of the "three-pipe problem" is the case histories of the victims of the extinction event, primarily those of the dinosaurs. Using cladistics, a system that uses phylogenetic relationships and the evolutionary history of groups of organisms to classify them, the authors examine common traits among all dinosaurs. Instead of the typical Darwinian "tree", this approach brings forth a pruned branch, where the most related groups are near the tip and the most distant near the base of the branch. Cladistics, the subject of contentious debate in some quarters of the paleontological community, attempts to take an objective look at evolutionary relationships: The more derived characteristics two species share, the more closely related they are. Using this approach, the authors conclude that birds arose from within one group of dinosaurs, primarily the theropods (which includes beasts like Tyrannosaurus rex). This view contends not only that birds descended from dinosaurs, but that the pigeons in the park are dinosaurian survivors of the great extinction (hence the name of the book).

The problem with this theory arises in what is called convergent evolution, whereby two totally unrelated groups evolve similar physical traits. Both insects and birds fly, for instance, but they are not related. Dingus and Rowe approach this problem by noting that the more traits shared, the more closely related two creatures may be. So-called anti-cladists would pose that the act of choosing a desirable trait among groups for cladistic analysis is subjective in itself.

There is a third, less pronounced section of this book that involves the evolution, dispersal, and extinction of the more contemporaneous birds. The immediate ancestors of these familiar creatures are less contentious among paleontologists. The authors therefore seem to regurgitate simple facts. What brings this section to life, however, is the suggestion based on the previous two sections that these creatures are not just "birds," but real dinosaurs. This may be a little difficult to accept, especially for those bird enthusiasts who enjoy their yearly counting forays. Calling our feathered friends dinosaurian survivors is one thing, but to describe John James Audubon as "the world's foremost authority on the living species of North American dinosaurs" is another.

Ultimately, the bird-dinosaur relationship is a matter of interpretation. The fossil record grows yearly. Each discovery has the potential to reshape our ideas. Despite Dingus and Rowe's arguments, one must not be so presumptuous as to claim full knowlege of the patterns in the fossil record. Cladistics has the potential to be a wonderful tool. Yet one must not be too hasty in pushing an interpretation based on an incomplete record. As a reader of The Mistaken Extinction, it might be wiser to mimic Sherlock Holmes sitting by the fireplace, smoking a few more pipes of tobacco, pondering the evidence a little longer.

Dinosaur Extinction: The Volcano-Greenhouse Theory - geologist Dewey McLean reviews the asteroid versus volcano extinction debate.

Dinofest - Web site of the Dinofest Symposium, being held April 17-19, 1998 at the Academy of Natural Sciences in Philadelphia. Issues dealing with extinction and dinosaurian evolution are being addressed there.

PaleoNet Pages - useful guide to discussions on the bird-dinosaur relationships and the Cretaceous extinction.

Journey into the World of Cladistics - introductory site on phylogenetic systematics. Maintained by the University of California Museum of Paleontology.

Timothy Rowe - co-author's home page discusses X-ray computed tomography as a tool for visualizing internal fossil anatomy.