The Enigma of the Extinction of the Dinosaurs

One of the more interesting contributions of paleontology to general knowledge is evidence that giant reptiles were once the dominant life forms on our planet. During the past two centuries some 5000 skeletal fragments of these creatures ha ve been excavated from Mesozoic sediments. Many are objects of public wonder in museum displays around the world. It is difficult to contemplate the skeletons of dinosaurs or large marine reptiles without also being reminded of their mysterious disappearance. Tn spite of a voluminous literature on the subject, there is no consensus regarding the stresses which drove the giant reptiles to extinction. It has become apparent, however, that they vanished in a general biotic crisis, and in recent years more attention has been focused on theoretical models which would produce stresses on a global scale. The problem of the extinction of the dinosaurs is thus clearly an inter­ disciplinary one. Unfortunately, the competence of a single author is necessarily limited. The review that follows represents the perspective of one student of the great reptiles who is greatly vexed by their apparently sudden disappearance at the end of the Mesozoic Era. The peculiarities of this extinction are summarized and various possible agents of biotic stress are briefly discussed. The Cretaceous-Paleocene (Mesozoic-Cenozoic) boundary, correspond­ ing to the extinction event during which the dinosaurs disappeared, occurred about 65 million years ago. The Maastrichtian Stage is the final major biostratigraphic division of the Cretaceous and the Danian Stage the first of the Paleocene. For examples of current geochronologic scales, see Van Hinte (1976) and Berggren (1971), noting that the absolute ages given are only approximations of actual values (Jeletzky 1978).