The Cambrian Explosion and the Fossil Record
edited by Junyuan Chen, Yen-nien Cheng, and H.V. Iten,
Bulletin of National Museum of Natural Science, Division of Collection and Research, National Museum of Natural Science, 1, Kuan-chien Road, Taichung, Taiwan, December 1997, 319 pages
Reviewed by Lisa-ann Gershwin,
Department of Integrative Biology, University of California, Berkeley CA 94720, USA.
"Wow!" was my first reaction, and it will certainly be yours as well. This multidisciplinary book, which is the product of the Cambrian Explosion Symposium in Nanjing, China in April 1995, brings together 16 papers on everything from algae to sponges to chordates, and from isotopes to taphonomy to geochemistry. There is truly something for everyone in this volume. But possibly the number one reason to covet this book is the huge collection of color photographs of some of the world’s most stunningly preserved fossils. The focus is on the fauna, with almost 200 pages devoted to descriptions of new taxa, reinterpretations of old taxa given new preservational information, and hypotheses about form and function.
The book begins with "The Meaning of the Cambrian Explosion" by Dolf Seilacher, which sets the stage with a review of some prevailing ideas in Precambrian studies and some of the main innovations of the Cambrian fauna (e.g. trace complexity, skeletonization, bioturbation, the diversity of trophic guilds).
The primary paper of the volume (Biology of the Chengjiang fauna, by Chen and Zhou) covers nearly 100 pages and much of the "wow!" in glorious full-color photographs. The magnificent preservation, biological diversity, and sheer quantity make this a collection of extreme importance. The paper presents well over 100 of the most spectacular specimens from the collection of 15,000 recovered so far. I could write endlessly about the beauty of the collection, but suffice it to say that I cannot imagine anyone will be disappointed. With that said, however, let me now highlight a few oversights that make this paper a little difficult to read and a little bit annoying. Firstly, the format of the paper was confusing, as I repeatedly found myself flipping back and forth between the two complementary sections, "fossil evidence of disparity" and "systematic paleontology" in order to glean all the information about any given taxon, some of which were never actually treated after their introduction. Secondly, the figures would have benefited substantially by the inclusion of scale indications. For some taxa, approximate sizes are given in the text, but not for all. Quite frankly, I felt a bit irritated at having to work so hard to find the relative sizes - that is the author’s job, not the reader’s. Thirdly, I was a bit put off by some of the conclusions in this paper, as I felt that they lacked a clear progression of reasoning. I found myself wanting to accept the ideas of Chen and Zhou, but unable to arrive at the same conclusions given the information presented. For example, their interpretations of two ctenophores left me quite puzzled. Both were interpreted as having a membranous skirt, although I found it difficult to agree from the facts provided. Furthermore, one of the genera was classified into the Ctenophora based on its possession of aboral papillae despite its tetraradiate symmetry and absence of comb rows. However, Chen and Zhou failed to mention that numerous species of jellyfishes have aboral papillae and are, of course, tetramerous and lacking comb rows. In another example, their restoration of a new algal genus left me similarly puzzled. They picture it as a bubble with numerous filaments hanging down, but fail to explain this construction in the text. I was unable to find evidence of a bubble in the photographs. Fourthly, I never did come to terms with Figures 76 and 77, which are supposed to be different as indicated by their specimen numbers, but look very similar to me. All this left me wondering what additional mistakes I had failed to notice. Despite these annoyances, I still learned many things from the paper and gained a deep appreciation of the Chengjiang collection through the vast amount of information presented.
In a paper as similarly stunning as the Chen and Zhou article, the affinity of Yunnanozoon, previously incertae sedis, seems finally convincingly interpreted as a chordate. Chen and Li provide not only many excellent color photographs, but also a good explanation of their comparison of Yunnanozoon with the Recent chordate Branchiostoma. However, like the Chen and Zhou paper, this one fails to consistently provide a sense of scale in the figures, but also adds the annoyance of often referring to specimen numbers rather than figure numbers in text discussions. No doubt to be the topic of much future discussion, this paper proposes the powerful hypothesis that a Yunnanozoon-like ancestor gave rise independently to the sister groups Tunicata, Cephalochordata, Conodonta, and Agnatha. Unfortunately, only a single paragraph was devoted to this idea, with only the most casual reasoning. I would like to take Chen and Li to task on this for my gut instinct is that they are onto something worthy of much more explanation.
I must not neglect a few other papers of specific noteworthiness. In one, Chuang reports on an interesting study of the functional morphology of Recent brachiopod ridges, and their usefulness in the identification of fossil taxa. However, I was left wondering whether this sort of non-taxonomic work actually constituted a legitimate species description, as mentioned in the abstract, or whether this created a nomen nudum. In another, Babcock and Chang give a fascinating interpretation of the taphonomy of Naraoia spp. through disarticulation experiments on the Recent horseshoe crab (Limulus polyphemus). While I was particularly surprised to learn that most Limulus specimens "remain nearly complete for at least two years" under anoxic and undisturbed conditions, it would have been helpful to know the number of replicates used in their various experiments. Possibly my favorite paper, next to the one by Chen and Zhou, was Zhu’s 38-page report on the trace fossils across the Precambrian-Cambrian transition, and their implications in defining the Pc-C boundary. A good review of the different types of traces is given, followed by an interesting discussion of trends in complexity through the Pc-C transition. Although this paper suffers from issues of scale and spelling, I found it to be particularly well constructed and well reasoned.
The remaining papers are certainly worth reading. Zhang et al. report on stable carbon isotope changes across the Neoproterozoic-Cambrian boundary. Tang et al. present their SEM work on resolving the nature of the grains in granular phosphorites, accompanied by 27 black and white images; Nedin concludes from laboratory findings that early mineralization is controlled by oxygen availability and pH. Siegmund discusses phosphogenesis as enhanced by microbial organisms. Zhang et al. review the distributional and geochemical implications of volcanic metabentonites. Popov and Zhang describe the distribution of calcareous algae, while Popov describes their diversity; Li details the systematics and diagenesis of 6 species of endolithic algae, with 31 photographs. Yin provides 10 color photographs and an additional 10 black-and-whites to accompany the study on acritarch biostratigraphy across the Precambrian-Cambrian transition. And Qian proposes a revised classification of the hyoliths based on 7 chronostratigraphic stages.
Because of the importance of the Chengjiang collection and the magnificent presentation of it in this volume, without doubt many of the papers in this book will be the subject of much discussion in the years to come. I heartily recommend this book to both professionals and students, for its broad scope will certainly appeal to a variety of interests. Overall, it takes the reader on a fantastic journey of wonder and amazement through the various biological and physical aspects of the Cambrian Explosion.
Copyright: Palaeontologia Electronica, 15 March 1999