Annalisa Berta leads readers through a vast range of topics regarding the evolution of marine mammals in Return to the Sea: The Life and Evolutionary Times of Marine Mammals. In this volume geared towards non-specialists (one might even suggest non-scientists), topics ranging from systematics, speciation, diversification, paleoclimate, paleoecology, ecology, and conservation of Cetacea, Sirenia, Desmostylia, Pinnipedimorpha, and other marine mammals are explored. It is also filled with the exquisite artwork of Carl Buell, who both illustrates modern marine mammals exhibiting a wide variety of fascinating behaviors, as well as fossil marine mammals with well-informed reconstructions of their soft tissue anatomy. The only disappointment with Buell’s work is that it is all reproduced in grayscale, with the exception of the cover illustration, depriving the readers of the richness of colored tones normally exhibited in his work.

The structure of the book is such that some topics are covered in subject specific chapters (Marine Mammals; Past Diversity in Time and Space, Paleoclimates, and Paleoecology; Ecology and Conservation), whereas others are covered in taxon-specific chapters (Pinniped Diversity, Evolution, and Adaptations; Cetartiodactylan Diversity, Evolution, and Adaptations; Diversity, Evolution, and Adaptations of Sirenians and Other Marine Mammals). It also contains a helpful glossary for perhaps unfamiliar terms that are bolded in the text, and a further reading and online sources section for additional information on each chapter.

In addition to the Buell illustrations, each of the chapters also include call-out boxes, charts, diagrams, and fossil reconstructions drawn from other sources, particularly from Berta’s recently updated textbook on marine mammal evolution (Berta et al. 2006). While for the most part very helpful, some of the illustrations could have been more so, and others include errors. For example, in the section on past diversity, there is a series of illustrations that include the “major” marine mammal fossil sites around the globe. While it is understandable that not all fossil sites could be included on such maps, there are some glaring exceptions that are missing, such as cetaceans from the southeastern United States in the Eocene, the Pacific Northwest and South Carolina in the Oligocene, and the US East Coast in the Miocene. Figure 2.8 shows five different “major” sirenian fossil sites in South America during the late Oligocene to early Miocene, when there is actually only one minor site. Strangely, neither of the sources cited for the information in these maps include these errors, and a comprehensive database of all fossil marine mammal fossil localities has been compiled in the Paleobiology Database (paleodb.org). Also, some of the taxa are clearly misidentified in the Buell illustrations. In Figure 2.7, the cetacean in the water is clearly Basilosaurus based on the size of the head relative to the body; in Figure 2.9, Simocetus is labeled Simocyon; and, in Figure 2.11, Hydrodamalis is misidentified as Desmostylus hesperus.

The content of the chapters is accurate, informative, and clearly based on recently published studies on both fossil and recent marine mammals. I particularly appreciated the paleoecology section, as it showed how the evolution of marine mammals was deeply intertwined with the past positions of the continents, evolution of Earth’s oceans, and with other oceanographic factors like temperature, salinity, and productivity. I also liked the discussion of modern marine mammal ecology as a way of demonstrating how we use what we know about modern marine mammals to help understand the evolution of these anatomical structures and behaviors in fossil animals.

As is typical for science books geared to the non-scientist, there are no references included in the text, except in some of the figure captions. The prose makes it clear to the reader that marine mammal science is an active field, and that the observations discussed in the book are drawn from a wide variety of paleontological and neontological works. I wonder, though, if we are not doing our non-scientist readers a disservice with this writing format. By removing the in-text citations that would be expected in a scientific work, we are depriving the readers of the opportunity to see exactly how many different scientific studies are used to construct a single paragraph in a book such as this. It also deprives the reader of the ability to track down the original sources if they are interested in learning more on a particular topic. This is clearly not a condemnation of this book in particular, but it is something on which we as scientists attempting to communicate with the general public (as well as publishers who specify the styles for such books) should ruminate.

The major strengths of Return to the Sea are its beautiful illustrations and its wide breadth of subject matter. The text, illustrations, and supplementary information are all well written, fascinating and compelling, and should be of great interest to the general reader, but almost all of the topics covered are too short to do them justice. It might have even been helpful to cut some sections that are extremely short, in order to give more about others and keep the book overall at the same length. For example, the information in the one paragraph-long section on whale fall communities is fascinating, but to really cover this topic for a general audience would have required several pages. The table of contents lists chapter titles and secondary headings, while the book uses an additional tertiary heading as well. The average length of the sections under the secondary headings is only around 4.2 pages long, with many of them only one or two pages long, and many of the tertiary sections include only a single paragraph. Given that Return to the Sea is 206 pages long (174 pages excluding the Glossary, Further Reading, Illustration Credits, and Index), includes 92 figures, three tables, and ten call out boxes, this leaves precious little space for the text to develop some very interesting and sometimes complex ideas.

Finally, the end of the book was rather abrupt. Following a paragraph on recovery and rehabilitation programs comes the glossary. There is no summary, or final thoughts on the subjects covered in the book, which left me wanting some sort of closure or a view to the future on this dynamic subject matter.

Return to the Sea: The Life and Evolutionary Times of Marine Mammals is a good primer on the subject of marine mammals, their origins, and their complex relationships with the evolution of Earth and its marine environment over the Cenozoic. Readers will undoubtedly be fascinated by many facets of marine mammal evolution and paleoecology, and will be enchanted by the lovely and accurate illustrations of extinct animals. Hopefully, those who read this book will have their interest sparked to continue to follow the rapidly accelerating discoveries in marine mammal evolutionary biology and paleontology as they continue into the future.