Fossils were at one time classified primarily by similarities of structure of the hard parts of organisms. This was found to be misleading as paleontologists discovered that some entirely unrelated creatures had developed similar structures, presumably because they were useful to different organisms that had adopted similar ways of life. This trick of nature, which Professor George Gaylord Simpson has called the "bane of the taxonomist," is called convergence.

Perhaps the most obvious example is that intelligent animal the porpoise, which has evolved a body shape and structure first adopted by the ichthyosaur 100 million years ago. Size, shape, and placement of front flippers are similar. Yet the ichthyosaur was a reptile related to the dinosaur; the porpoise is a mammal, albeit a sea-dwelling one, related to man. If both were known only from their gross outlines, they might have been classified in the same family or even the same genus, when in reality they are not even of the same class.

Convergence of a type more potentially confusing to the paleontologist occurs in a case such as that of the horn corals, which are coelenterates, the rudistid clams, which are mollusks, and some brachiopods, all of which in some extinct species took the form of a cone attached by its small end to the sea bottom or some other anchorage. Although they belong to three different phyla, they can be told apart only after close study.

The phenomenon of convergence is only one of the problems that classifiers of fossils face, working as they often must with the fragmentary or imperfect evidence that time has left them. But occasionally they have a stroke of luck. This happened to Dr. H. B. Fell of Victoria University, Wellington, New Zealand, in the course of a long study of the evolution of starfish. From the British museum he obtained part of a "living fossil," the dried arm of a sea star or somasteroid, an animal previously known only from fossils of 400 million years ago, when it was presumed to have become extinct.

From a detailed anatomical study of the tissues (not possible from fossils) and later of specimens caught alive in the Pacific off Nicaragua, he confirmed that the arms of somasteriods had structures like the arms of crinoids but that the body was flat and shaped like a starfish. He described the "living fossils" as "the oldest type of astrozoan (starfish) echinoderm yet discovered" and suggested that "the marked resemblance to crinoids now evident in somasteroids" made it probable that all star-shaped echinoderms had descended from crinoids.

Such geneological researches excite the spirit of discovery and tax the skills of professionals. They are beyond the reach of amateurs, but the thrill of finding a beautiful fossil by hard work and the pleasure of preparing it are the collector's reward. They are his school and his deepest pleasure.

Furthermore, he can enjoy his specimens for themselves, for fossils are often beautiful, like ancient sculptures or rare gems and minerals. Amber, pale and waxy, or vibrant with glowing hues of reddish brown, a showcase of ancient insects. Pyritized brachiopods and snails miraculously transformed to brassy gold, and the theatrical contrasts of pyritized starfish and trilobites on coal-black slates from Germany. The impudent faces of trilobites, like African carvings in ebony, peering from their tombs of 400 million years ago, and the bold splashes of color in an agatized log from Arizona.

Besides this aesthetic appeal, fossils have an appeal rooted deep in life itself. They once lived. To be able to hold a fossil in your hand, to imagine what sunrises and sunsets it saw eons ago in a world that we can only dimly imagine, is something that transcends ordinary experience. This is, as William Blake wrote:

To see the world in a grain of sand, And a Heaven in a wild flower;

Hold infinity in the palm of your hand, And eternity in an hour.

In a like mood, Professor Simpson wrote: "Our allotted span is a few years, and most of us can see with our own eyes only a minute part of the earth around us. But our minds need not be restricted to these narrow limits of time and space. They can range through the past and can see all the curious creatures and scenes of life's history in ever-changing sequence. A fair title for a book on paleontology might be, 'How to Live a Billion Years.' "

0 0

Post a comment