A catalogue of the Mesozoic Mammalia in the Geological Department of the British Museum

Abstract

INTRODUCTION The history of mammalian life in the Cainozoic, the so-called “ Age of Mammals,” has occupied the attention of several generations of paleontologists. Great collections have been brought together from all parts of the world, and however many gaps remain to be hlled, at least the broader lines of mammalian evolution during this era are now well understood. Few, however, stop to realize that, even were Cainozoic history completely known, only a fraction of the evolution of the Class Mammalia would be made clear. The mammals were already well advanced at the beginning of the Eocene : it has been estimated that two-thirds of their total development from the reptilian to the recent mammalian type had already taken place by the end of the Mesozoic. This lost two-thirds, this mammalian prehistory, is much more basic in character than the relatively minor differentiation which took place in the Cainozoic. It must contain the answers to the most fundamental problems of mammalian classihcation and phylogeny, to which later mammals, taken by themselves, always and inevitably yield only equivocal, misleading, or incomplete clues. Only the Mesozoic mammals can cast direct light on these basic early stages, but they have long been either neglected or clouded by misinterpretation or erroneous observation. The reason for this condition of affairs is, however, not far to seek. The remains of Mesozoic mammals are among the smallest, the rarest, and the most fragile of fossils. Very few students have been able to make any considerable hrsthand study of them ; the last general review of the subject was made just forty years ago. Binocular microscopes were not then available, knowledge of other mammals, especially of fossil mammals, was much less complete than now, and, most important of all, no one had been enabled to study both American and European forms and to make adequate syntheses and comparisons. Some of these disabilities can now be removed. Of the remains of Mesozoic mammals, only the more precious for their great scarcity, a very considerable number is in the British Museum (Natural History). Here is Tritylodon, the oldest known mammal skull ; here is one of the two original jaws brought to light by Broderip and studied by Cuvier ; here, with one exception, is the entire priceless Purbeck collection ; here are all the known Lower Cretaceous mammals ; here, too, are other invaluable representative specimens from the Rhaetic rocks, the Stonesfield Slate, and the Upper Cretaceous formations. It is upon this classic collection, which will always remain the fundamental basis for the study of Mesozoic Mammalia, that the present monograph is based. All the other still extant material of European Mesozoic mammals has, however, also been studied and is included. For the Triassic forms the collections at Stuttgart, Tubingen, Bath, and Yale University have been drawn on, in addition to that of the British Museum. The Stonesfield specimens are in the Oxford, York, Museum of Practical Geology, and British Museum collections. One Purbeck jaw is in the Museum of Practical Geology. Far the greater number of all the specimens known are in the Beckles collection from the Purbeck beds, purchased by the British Museum in 1876. In addition to the acknowledgments made in the preface, the author wishes especially to thank Dr. F. A. Bather and Mr. A. T. Hopwood, who have placed the British Museum collection and every facility for its study at his disposal, and who have constantly assisted and encouraged the progress of the work.