In Pursuit of Early Mammals

In Pursuit of Early Mammals

In Pursuit of Early Mammals

In Pursuit of Early Mammals

Synopsis

In Pursuit of Early Mammals presents the history of the mammals that lived during the Mesozoic era, the time when dinosaurs ruled the Earth, and describes their origins, anatomy, systematics, paleobiology, and distribution. It also tells the story of the author, a world-renowned specialist on these animals, and the other prominent paleontologists who have studied them. Zofia Kielan-Jaworowska was the first woman to lead large-scale paleontological expeditions, including eight to the Gobi Desert in Mongolia, which brought back important collections of dinosaur, early mammal, and other fossils. She shares the difficulties and pleasures encountered in finding rare fossils and describes the changing views on early mammals made possible by these discoveries.

Excerpt

Since the demise of non-avian dinosaurs some 65 million years ago, modern mammals—that is to say, marsupials, placentals, and monotremes—have become conspicuous, diverse elements of Earth’s biota. But the family tree that includes mammals and their nearest relatives (mammaliaforms, in technical parlance) is far more deeply rooted in time, extending back to perhaps 220 million years ago. Clearly, then, the varieties known from the “age of mammals” that followed dinosaur extinctions represent only the uppermost boughs of what is increasingly being revealed as a bushy, complex tree.

Knowledge of early mammalian history—the lower part of that tree—has long been limited by a fossil record that is disappointingly sparse, even to those paleontologists who set a low bar when it comes to basic data. Fossils are generally tiny, fragmentary (most species are known by isolated teeth or jaw fragments), and incredibly hard to find. the dawn of discovery took place in the late nineteenth century. Synthetic study of these fossils, almost all from Britain and the western United States, was completed in the 1920s by the great evolutionary biologist G. G. Simpson. It was also at this time that the first mammalian skulls of Mesozoic age were discovered in Cretaceous rocks of Mongolia. Simpson recognized the existence of various now-extinct Mesozoic mammal lineages, as well as representatives (or, it now appears, relatives) of modern groups. But this early period of discovery and study raised fundamental questions that could not be addressed with the existing record. Did the egg-laying platypus and echidnas of Australia and New Guinea, for example, independently evolve from “reptilian” precursors? Meaningful biological interpretation also remained beyond reach: about all one could say is that early mammals were generally small, shrew-like creatures that probably preferred an insect-based diet. (The stereotype has persisted: as this book shows, it is erroneous.) Early mammal history had emerged from total darkness, but remained in the shadows.

The situation has changed profoundly in recent decades. a new period of fossil discovery began in the mid-twentieth century and its pace has quickened to a dizzying rate. a number of species are now known by breathtakingly complete specimens, some even preserving remnants of fur. Long-term, dedicated effort has resulted in the collection of large samples and comprehensive assemblages for some areas and time intervals. Informative fossils have been recovered from most major landmasses, and though substantial gaps in the record persist, much of the Mesozoic time scale has been sampled. And, of course, many . . .

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