Mammoths, Sabertooths, and Hominids

by: Jordi Agusti, Mauricio Anton Written for the specialist or student in evolutionary biology and paleontology this book can nevertheless be studied by anyone who has an interest in these topics. For this reviewer, the main interest in this book was in the effect of climate on mammalian extinctions, with the hopes of shedding light on the current debate on climate change/global warming. Since the book is directed towards the specialist, the non-specialist will have to deal with a large amount of terminology, this arising mostly from the classification schemes used in paleontology and zoology. This reviewer found it helpful to use a few note sheets along the way to assist in remembering some of the scientific names of the major fauna that did exist in the time frame over which the book covers. Having some background in biology and geophysics will also help in the assimilation of the material in the book, particularly in cases where the authors are discussing dating techniques. There is no part of this book that is uninteresting, and the excellent plates and drawings in the book add to the pleasure in its perusal. And the book went beyond this reviewer's expectations regarding the effects of climate change on mammalian extinctions: there are many examples discussed in the book and a few surprises, such as the assertion that the Mediterranean was completely desiccated around 6,000,000 years ago (the late Miocene). Early on though the authors caution the reader that even though much is known now regarding the time series of temperatures and oceanic changes throughout the last 65,000,000 years, one cannot conclude that there is an exact correlation between changes in climate and changes in mammalian ecosystems. Very interesting also is how the authors deduce the dietary habits of extinct mammals by examining their fossilized teeth and jawbones. This "comparative" paleontology allows one to ascertain what flora were more prevalent in ages past by comparing the dental arrangements of modern mammals with those that are extinct. The variability in dental morphology it seems does have a direct correlation with the floral that were present during the time frame that the mammal was alive. An excellent example of this, which the authors discuss in the book, is the presence of `hypsodonty', which is dental morphology wherein the teeth have high crowns and enamel that extends beyond the gum line. The authors explain this as an adaptation to the silica grains that would be present in the grasses of the Pliocene age. Mammals without this adaptation would face extinction pressures due to the quick abrasion of the teeth due to these grains. Another interesting discussion in the book concerns the `Monterey hypothesis', which is an attempt to understand the "climate crisis" in the middle Miocene in terms of the sequestering of large quantities of organic carbon. This resulted in accelerated global cooling because of the drawdown of atmospheric CO2 and the end of certain warm-water circulations. The authors discuss the experimental evidence for this hypothesis. Mammalian extinctions can therefore be caused by climate change as well as genetics. The authors however point to another cause of these extinctions, namely the rise of the homo sapiens species, which the authors characterize as being "unique" in "its ability to exterminate other species." They give evidence to support this, but also note that that modern humans also fall prey to the very mammals that benefit from human expansion, such as the rats in the Middle Ages. But as they also note, H. sapiens is a wandering species. They moved into Australia as well as North America, and of course now dominate the planet. But this species, which on rare occasions decimates its own, is insatiably curious and has shown absolute brilliance throughout its sojourn on Earth...and on other worlds where it is just getting started.