Reviewed by Ephraim Nissan (London, England)

Holman, J. A. 2018. Fossil Frogs and Toads of North America. Life of the Past series. Indiana University Press, Bloomington. xiii + 247 pp. ISBN 10: 0253031745, ISBN 13: 9780253031747. ($21.00 paperback/e-book with 30% PS discount.)

“Oddly, no such comprehensive study exist[ed]” (p. ix) until Holman’s book under review. J. Alan Holman (1931–2006), a paleoherpetologist and (in neontology) a herpetologist, was also the author of Fossil Snakes of North America (Indiana University Press, 2000). A reprint of his 2003 book, this volume also describes modern anuran (frogs and toads) species, and as some fossil taxa still exist as living species, their diagnostic skeletal elements are also described.

Holman (in Ch. 3) proceeds epoch by epoch in his discussion of anurans: from the Mesozoic, through the Tertiary, to the Pleistocene. The cover image shows a freshwater surface (apparently a river) during a storm, illuminated by lightning. On the river in front, we see anurans. On the other bank, we see in profile the silhouettes of mammals in the distance, some of them looking scared (because of the lightning), and a few easily identifiable as brontotheres (because of the two-pronged horn on their snout), so this clearly is a scene from the Tertiary.

The preface remarks that in 1930 in Spicer County, Minnesota, the leopard frog (Rana pipiens) was so abundant, that at the first frost, a particular frog gatherer saw them form “a band two rods wide and one-half mile long where no one could step without crushing frogs” (p. ix). (There are frog gatherers and frog gatherers: those selling them for food in Sicily in earlier generations used to advertise them by calling out “Pisci cantannu!”, i.e., “singing fish.”)

The table of contents is faced with a punning sentence standing alone on the otherwise blank preceding page: “All the frogs of which you are about to read have croaked.” This is not entirely true, as some species are extant. But then again, you cannot get the skeleton (other by X-ray) of a specimen of an extant species unless that specimen has died.

The introduction begins with an overview of the anurans and a short history of studies into fossil anurans, before turning to describing the anuran skeleton in general, and individual bones in particular, insofar as these are used by paleontologists. The Introduction also outlines the early evolution of the anurans and defines the chronological terms.

Of the three numbered chapters, Ch. 2 is “[t]he heart of this book” (p. x). It spans pages 38 to 186 and provides detailed systematics with each taxon’s localities of occurrence, diagnoses guiding recognitions, and illustrations: drawings of bones, photos of bones, as well as consensus trees (not cladograms) of the phylogenies; and, for extant taxa, color plates illustrating photos of living species.

“Systematic Accounts” (Ch. 2) is followed with “Chronological Accounts” (Ch. 3), “stressing the changes in taxonomic content of each epoch, and with a special overview of the Pleistocene” (x). The Epilogue begins by explaining: “This is a long epilogue, as epilogues go, because the classification and the phylogeny of anurans are in an embryonic state, owing to a poor fossil record” (217), and suggesting you may even “find out what an epilogue really is” (217). Which is another example of the author smuggling in his welcome humor.

He quotes a statement (made in 2000) to the effect that gaps in the fossil records of amphibians are so big that “understanding of the interrelationships of the principal groups of amphibians remains incomplete” (p. 217), so giving cladograms would be misleading. And indeed, Holman gives none.

The epilogue discusses the problems: incorrect naming; “intercolumnar variation, or the lack of it, in presacral frog vertebrae” (p. 218); ontogenetic variation (these are animals that undergo metamorphosis, as well as growth and aging); variation caused by environmental conditions; finger and toe regeneration if these were severed; and bone size and shape variation in the same species based on geographic area.

“[U]ntil shortly before World War II, the vertebrate paleontological community was mainly engaged in the collection, exhibition, and study of large fossil vertebrates” (p. 220), whereas the purposeful collection of microvertebrate fossils spread after WWII, “by simple washing and sieving techniques” (p. 220). The latter should be “routinely done on all vertebrate fossil digs” (p. 220), Holman recommends at the end of the Epilogue.

After the bibliography (pp. 221–235), and figure credits, a general index follows, then a taxonomic index, and a site index, the latter being clustered by U.S. state, plus Chihuahua, Nova Scotia, Ontario, Quebec, Saskatchewan, Sonora, and Tamaulipas. The entries with most lines are those for Florida, Kansas, Nebraska, and Texas.

Clearly, the late Holman deserves our gratitude: his books on snakes and anurans in North America’s fossil record are an important legacy.