CONTENTS 



Page 



Letter of transmittal xix 



Preface i xxi 



Vertebrate paleontology in the national surveys xxi 



Preparation of the present monograph xxi 



Work by the author, 1878-1919 xxii 



Research and collaboration xxii 



Cooperation of museums xxiii 



Work on text and illustrations xxiii 



Summary of geologic and anatomic principles xxiii 



Chapter I. Introduction to mammalian paleontology 1 



Section 1. Exploration and research made in the preparation of this monograph 1 



Section 2. Preliminary survey of the monograph and the conclusions presented 2 



Range of the titan otheres in geologic time 2 



Hay den's subdivisions of the Eocene and the Oligocene 5 



Discovery of the titanotheres of the plains 6 



Discovery of the mountain-basin environment of the titanotheres 6 



Discovery and delimitation of periods of sedimentation and of life zones 8 



Principle of local and continental adaptive radiation 10 



Comparison of the four life phases of Europe and North America during Eocene and early Oligocene time 12 



Old and new systems of classification 13 



Old terminology retained 13 



Linnaean methods of defining species, genera, and phyla of titanotheres 14 



Recognition of many lines of descent; polyphyly the key to interpretation of the family 14 



Relation of the phylogenetic classification to the Linnaean classification 15 



Comparison between zoologic and paleontologic species 18 



Proportions of the skull in bears and in titanotheres 19 



Features distinguishing phyla of titanotheres - 19 



Mutations of Waagen 19 



Zoologic and paleontologic nomenclature 20 



Summary of differences between old and new systems 22 



Study of the evolution of single characters 22 



Phylogeny of the nine typical families of the Perissodactyla 23 



Wide geographic distribution of the Perissodactyla 24 



Causes of evolution 27 



Adaptive evolution and overs volution of the form of skull, tooth, and foot 27 



Phyletic divergence in the evolution of new proportions in horses and in titanotheres 28 



Evolution of the limbs and feet of the titanotheres 33 



Origin of new characters as distinguished from changes in proportion 34 



Velocity in the development of characters and in phylogeny 39 



Summary of the evolution of the titanotheres 41 



Section 3. Bibliography of literature cited or consulted in the preparation of Chapter I 42 



Chapter II. Environment of the titanotheres and effect of adaptive radiation on their variation 43 



Section 1 . Geology and geography 43 



Correlation of early Tertiary events in the Rocky Mountain region with those in western Europe 43 



Late Cretaceous and early Tertiary climates 45 



Eocene geography of western North America and its relation to f aunal migrations 47 



Geographic divisions and their bearing on migration 47 



Character of the mountain-basin, plateau, and plains regions 51 



Eocene topography in the Rocky Mountain region 51 



Contrast in phj-siographic conditions east and west of the Rocky Mountain Front Range 53 



Lateral and main river systems in the mountain-basin region 54 



Section 2. Eocene and lower Oligocene formations and f aunal zones 56 



First f aunal phase (basal Eocene) 56 



Seventeen life zones 56 



Basal Eocene time in Montana and New Mexico 60 



Summary of faunal events of basal Eocene time 60 



Basal Eocene faunal zones 63 



Zones 1 and 2: Ectoconus and Polymastodon zones (Puerco fauna; part of Thanetian of Europe) 63 



Zones 3 and 4: Deltatherium and Pantolamhda zones (Torrejon and Fort Union faunas; part of Thanetian 



of Europe) 64 



