Journal of Vertebrate Paleontology 21(1):201–202, March 2001 q 2001 by the Society of Vertebrate Paleontology
REVIEW
FOSSIL SNAKES OF NORTH AMERICA: ORIGIN, EVOLUTION, DISTRIBUTION, PALEOECOLOGY, by J. Alan Holman, 2000. Indiana University Press, 357 pp. 1 xi, hardback, $69.95, ISBN 0-253-33721-6.
Growing up in the ‘‘Low Country’’ of South Carolina, it was quite easy for me to develop a strong interest in both paleontology and herpetology at a young age because of the abundance there of both fossils and snakes (but not necessarily fossil snakes). Being unable to decide whether I should pursue paleontology or herpetology as a career, however, I still distinctly remember the moment at the dinner table when I announced to my parents that I was going to become a paleoherpetologist when I grew up. Well, that is not exactly the career path I chose, but thank goodness Al Holman did! His recent book, ‘‘Fossil Snakes of North America,’’ has been long anticipated and will likely remain the definitive reference on the subject for many years to come. As with any book review, it is only fair that both highlights and deficiencies be noted. Therefore, I will dispense with a series of minor disappointments first, then move on to why I feel the book is both important and enjoyable. Holman’s book is obviously intended for the serious student of fossil snakes and is therefore a ‘‘must have’’ for that group. It also should be in the library of any vertebrate paleontologist whose projects regularly involve screen-washing late Cretaceous through Pleistocene sediments in search of microvertebrates, and it would be helpful to anyone who maintains a broad spectrum of interests across our field, as well. The price ($69.95) places the book within the realm of obtainable, in contrast to some rarified prices we have seen lately, such as the $260 for Janis, Scott, and Jacob’s ‘‘Evolution of Tertiary Mammals of North America.’’ Even Korth’s (1994) comparably sized and similarly focused ‘‘The Tertiary Record of Rodents of North America’’ now lists for $125.50 on Amazon.com! On the other hand, the price of ‘‘Fossil Snakes of North America’’ could have been even lower were it not for the 45 color plates of extant snake taxa, which, in a book on fossil snakes, seem somewhat out-of-place. The inclusion of such plates, however, is certainly helpful for the non-specialist including the audience of avocational herpetologists and paleontologists who may be interested in adding this book to their libraries. The book is divided into four chapters. The first chapter provides an introduction and begins with a short background on the study of fossil snakes. Once again we are reminded of the impact that Claude Hibbard’s screen washing techniques have had on the advancement of our profession. This chapter also reviews the major specializations of snakes, such as those related to locomotion, feeding, and sensing their surrounding environment, and a short section on the origin of snakes follows. The last nearly 50% of Chapter 1 is devoted to the identification of fossil snakes with particular emphasis placed on the morphology of trunk vertebrae, the most diagnostic of snake bones. The last two pages of Chapter 1 present the chronological framework for all that follows, and, in my opinion, are the most disappointing. However, two pages out of 357 are not bad. The red flag is first raised upon reading the caption for the figure on p. 17, which depicts the chronology for the North American Land Mammal Ages. The first reference in that caption indicates that Holman relied upon the temporal framework presented in the 1987 Woodburne volume on Cenozoic mammalian biostratigraphy. Since 1987, however, there have been several important revisions of the Cenozoic Time Scale, as well as NALMA boundaries, two of the most often cited of which include Berggren et al. (1995) and Woodburne and Swisher (1995). Even the briefest glance of this figure shows its ‘‘antiquity,’’ as the Chadronian was determined to be of late Eocene age, not early Oligocene, ten years ago (Swisher and Prothero, 1990). Other long outdated calibration points evident in this figure include those for the Cretaceous–Tertiary boundary, the Paleocene–Eocene boundary, and the Eocene–Oligocene boundary. Although the second reference in the figure caption implies that Holman used information provided in Prothero and Emry (1996) for the Eocene–Oligocene transition,
the figure nevertheless shows a date of 38 Ma rather than the 33.8 Ma date that has been accepted for over ten years, and also used in Prothero and Emry (1996). Another glaring error in this figure is the reversed position of the Irvingtonian and Rancholabrean Pleistocene land mammal ages. Furthermore, Holman’s use of Irvingtonian I and II plus Rancholabrean I and II, following Repenning (1987), has also been revised for some while now to Irvingtonian I, II, and III plus an undifferentiated Rancholabrean (Repenning, 1992). One more minor complaint: the figure should have been numbered. The second chapter provides a systematic account of nearly all known North American fossil snakes, with the exception of at least one omission (see below). Although detailed descriptions, diagnoses, and revisions of both include the traits necessary to identify the taxon in question if one has, primarily, a vertebra or vertebrae in hand (which is surely one of the main reasons Holman assembled this book), there is little differentiation as to whether these traits are primitive or derived. As Gardner and Cifelli (1999:87) noted, however, ‘‘polarities of vertebral features remain largely undetermined for snakes,’’ and such a differentiation is unimportant if one is using the book primarily for identification purposes. Just as Gardner and Cifelli follow ‘‘the historical practice of using unique combinations of vertebral features, rather than characters which are demonstrably apomorphic, to differentiate taxa of snakes,’’ so too does Holman. A classification, essentially that of Rage (1984), is provided at the beginning of Chapter 2, but, again, there is no detailed discussion or clarification with regards to the phylogeny of snakes. This is very likely a reflection of the current poor, or at least contentious, state of snake systematics. Still, I would like to have seen at least a little more on the history of the classification of snakes given the scope of this volume. I would have appreciated more discussion on snake origins, too (in Chapter 1), but most of the pertinent literature (e.g., several articles by M. S. Y. Lee and M. W. Caldwell) has only recently been published, probably after, or at least very near, the completion of this book. Holman only very briefly mentions the results of some recent phylogenetic studies, and to the delight of many, but to the disdain of many others, there is only one cladogram in the entire volume (Fig. 14). Returning to the missed taxon noted above, Holman apparently overlooked the report by Sullivan and Lucas (1988) of Sanjuanophis froehlichi from the early Eocene San Jose´ Formation of New Mexico. This oversight further manifests itself as an omission in Chapter 3 of a locality containing snakes of Eocene age in New Mexico, and of New Mexico representing a source of material for Cheilophis huerfanoensis and Calamagras primus, as well. Another disappointment is that very few figures in ‘‘Fossil Snakes of North America’’ were prepared specifically for this volume. Most were borrowed from earlier publications, and, as a result, the 127 figures of vertebrae in Chapter 2 naturally range in quality from excellent to poor and include a variety of artistic styles, which is a bit distracting. Many of these previously illustrated specimens should have been redrawn (or photographed)—particularly those copied from Gilmore (1938) including figures 16, 23, and the especially uninformative figure 48. Chapter 3 provides an account of the localities from which snake fossils have been reported, starting with those of Cretaceous age and continuing chronologically up through the Pleistocene. There are a few records missing, one in particular being that of Palaeophis from the Paleocene of South Carolina reported in Erickson (1998). Given that Holman was a reviewer of Erickson (1998), the omission of this record would seem to result from the book having gone to press prior to release of the volume in which occurred Erickson’s paper. But on page 322 of ‘‘Fossil Snakes’’ are two records ‘‘Added in press’’ from 1999 publications. I most enjoyed the final chapter. In it, Holman assimilates information
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from the previous three and provides the ‘‘big picture’’ pattern of snake evolution, biogeography, and paleoecology in North America through time. Holman shows that snakes in North America during the late Cretaceous, to a greater extent than even the mammals, appear to have been quite rare, small, and an insignificant component of the faunal landscape. In contrast to the dramatic expansion of the North American mammalian fauna during the early Tertiary, the record of snakes remains depauperate throughout the Paleocene and Eocene. Diversity appears to take a great leap forward in the Early Miocene, but we learn that it is in the middle Miocene that the North American snake fauna significantly expands into the profusion of ecological roles currently occupied by the modern fauna. By the end of the Late Miocene, after what Holman points out was ‘‘one of the most rapid evolutionary radiations of any vertebrate group’’ (p. 297), the fauna was essentially modern, at least at the generic level. By the end of the Pliocene, the fauna was nearly modern at the species level. The last part of Chapter 4 includes an interesting discussion on misplaced assumptions regarding the use of fossil snakes for the reconstruction of past habitats and climate, with particular emphasis placed on the counter-intuitive findings of evolutionary stasis and limited geographic range adjustments in snake faunas during the Pleistocene. In the section on range adjustments, Holman reviews the disharmonious communities concept of Lundelius et al. (1983) and introduces the non-specialist to hypotheses constructed to explain faunal climatic adjustments such as the ‘‘stripe hypothesis,’’ the ‘‘Pleistocene equability hypothesis,’’ the ‘‘Pleistocene specific response hypothesis,’’ and the ‘‘plaid hypothesis.’’ Returning to the idea of evolutionary stasis in snakes during the span of Pleistocene glacials and interglacials, Holman discusses several possible reasons. These include biases that may have been imposed by incorrect taxonomy and the difficulties in discriminating between taxa that have very similar vertebral morphology, as well as the retention of conventional ideas surrounding what was once thought to be the limited ecological and physiological tolerances of snakes. Holman further points out additional factors that may have contributed to their survival and stasis including the small size of many snakes, their independence from any apparent ecological relationship with the Pleistocene mammalian megafauna, their lack of parenting-imposed stress, and their apparent absence from the diet of North America’s early human inhabitants. In summary, we learn that snakes evidently had much broader ecological and physiological tolerances than previously considered. In the epilogue, Holman recalls his first encounter with a snake, a disastrous one for the latter, and he goes on to make a plea for the conservation of snakes, citing several examples of, and reasons for, their very recent and dramatic decline. And I am glad that Holman decided to end his book with a personal note; that is not often the case in scientific writing, but it certainly seemed appropriate in this case—in this culmination of a life’s work well done. L. BARRY ALBRIGHT III Museum of Northern Arizona 3101 North Fort Valley Road Flagstaff, Arizona 86001 Received and accepted October 2000.
LITERATURE CITED Berggren, W. A., D. V. Kent, C. C. Swisher, and M.-P. Aubry. 1995. A revised Cenozoic geochronology and chronostratigraphy; pp. 129– 212 in W. A. Berggren, D. V. Kent, M.-P. Aubry, and J. Hardenbol (eds.), Geochronology, Time Scales, and Global Stratigraphic Correlation. Society for Sedimentary Geology, (SEPM) Special Publication 54. Erickson, B. R. 1998. A palaeophid snake from the Late Paleocene of South Carolina; pp. 215–220 in A. E. Sanders (ed.), Paleobiology of the Williamsburg Formation (Black Mingo Group; Paleocene) of South Carolina, U. S. A. Transactions of the American Philosophical Society 88, pt. 4. Gardner, J. D., and R. L. Cifelli. 1999. A primitive snake from the Cretaceous of Utah. The Paleontological Society, Special Papers in Paleontology 60:87–100. Gilmore, C. W. 1938. Fossil snakes of North America. Geological Society of America Special Paper 9:1–96. Lundelius, E. L., R. W. Graham, E. Anderson, J. Guilday, J. A. Holman, D. W. Steadman, and S. D. Webb. 1983. Terrestrial vertebrate faunas; pp. 311–353 in S. Porter (ed.), The Late Pleistocene. University of Minnesota Press, Minneapolis. Prothero, D. R., and R. J. Emry. 1996. The Terrestrial Eocene–Oligocene Transition in North America. Cambridge University Press, Cambridge, 688 pp. Rage, J. C. 1984. Serpentes, Part 11, Handbuch der Pala¨oherpetologie. Wellnhofer, P. (ed.), Gustav Fischer Verlag, Stuttgart, 80 pp. Repenning, C. A. 1987. Biochronology of the microtine rodents of the United States; pp. 236–268 in M. O. Woodburne (ed.), Cenozoic Mammals of North America: Geochronology and Biostratigraphy. University of California Press, Berkeley. 1992. Allophaiomys and the age of the Olyor Suite, Krestovka sections, Yakutia. U. S. Geological Survey Bulletin 2037, 97 pp. Sullivan, R. M., and S. G. Lucas. 1988. Fossil Squamata from the San Jose´ Formation, Early Eocene, San Juan Basin, New Mexico. Journal of Paleontology 62:631–639. Swisher, C. C., and D. R. Prothero. 1990. Single crystal 39Ar/40Ar dating of the Eocene–Oligocene transition in North America. Science 249: 760–762. Tedford, R. H., J. B. Swinehart, C. C. Swisher, D. R. Prothero, S. A. King, and T. E. Tierney. 1996. The Whitneyan–Arikareean transition in the High Plains; pp. 312–336 in D. R. Prothero and R. J. Emry (eds.), The Terrestrial Eocene-Oligocene Transition in North America. Cambridge University Press, Cambridge. Woodburne, M. O. 1987. Cenozoic Mammals of North America: Geochronology and Biostratigraphy. University of California Press, Berkeley, 336 pp. Woodburne, M. O., and C. C. Swisher. 1995. Land mammal high–resolution geochronology, intercontinental overland dispersals, sea level, climate, and vicariance; pp. 335–364 in W. A. Berggren, D. V. Kent, M.-P. Aubry, and J. Hardenbol (eds.), Geochronology, Time Scales, and Global Stratigraphic Correlation. Society for Sedimentary Geology, (SEPM) Special Publication 54.