Significance of Fossils in Determining Evolutionary Relationships

Abstract

Fifteen years ago, I think it inconceivable that editors should have offered, or a reviewer accepted, a title such as mine. After all, evolution is a theory about the history of life; evolutionary relationships are historical relationships; fossils are the only concrete historical evidence of life; therefore fossils must be the arbiters of evolutionary relationships. Such an argument is implicit in most discussions of relationships during the last 120 years. As one recent example, Nash et al (65) write that The evolutionary origins and relationships of elasmobranchs are something of a mystery, due mostly to the lack of fossils. These authors are biochemists, presenting the myoglobin sequence of a shark, but readers will recall similar statements in their own fields. Such beliefs epitomize the tradition in which I was educated, and influenced my decision to take up vertebrate paleontology. After ten years work in that field, I read Brundin (10), and still recall the excitement with which I realized that there is a logical basis to evolutionary relationships which I had never seen discussed. Brundin was developing Hennig's thought (41-43), and in my view it is the dissemination and development of those ideas that have called the role of fossils into question, and necessitated this review. If received wisdom-that fossils are the truest guides to relationshipswere valid, it should be easy to compile instances. But instances of what? How can one recognize a valid contribution from the fossil record? First, I suggest that the problem of relationships solved, or illuminated, must concern living species, or groups with Recent members. For to find that relationships within or between extinct groups have been determined by fossils is of no interest here. After all, what else could be brought to bear on groups that contain nothing but fossils? Second, in order to recognize