Ammonites, A Brief Study

Ammonites by Neale Monks and Philip Palmer. Washington, D.C.: Smithsonian Institution Press, 2002. $50.00 cloth, $24.95 paper; 159 pp; 21 color plates, numerous B&W photographs and a few line drawings; glossary. This book is part of the Smithsonian’s “The Living Past Series.”

Monks and Palmer have produced the first Ammonite specific book since the 1981 work by Ulrich Lehmann, The Ammonites, Their Life and Their World, Cambridge University Press. Lehmann’s work contains more detail than the current work but contains scientifically “dated” material. Monks and Palmer have brought Ammonites up to date with the most recent research findings.

Introductory material in Ammonites begins with general information about cephalopods and their biology. This includes discussion of the ancient and modern nautiloids, their anatomy and their relatives. The modern chambered nautilus has generally been the model for our understanding of the ammonites since the their extinction at the end of the Cretaceous and since the nautilus is the only surviving cephalopod with an external shell. Monks and Palmer delve into the anatomy and biology of the modern nautilus in some detail.

The bulk of Ammonites is involved with the discussion of the ammonites in particular. Fossil ammonite morphology is presented at length as the authors describe siphuncle arrangements, coiling and ornamentation, and suture patterns. Soft body anatomy is highly conjectural with few ammonites preserved with enough soft body preservation to provide conclusive information. One of the unresolved issues with ammonites is a preserved structure called the aptychus. This butterfly shaped device has been described either as a “trap-door” covering the animal when it withdrew into its shell or as preserved jaw structures. During this discourse, the authors make many comparisons with modern and fossil cephalopods including squid and octopus.

The reader may be frustrated by the absence of conclusive information on many aspects of ammonite biology. There is much to be confused about. Some of the fossil evidence indicates that the opening of some (but not all) coiled ammonite shells pointed up rather than horizontally as it does in the modern nautilus - this would certainly make our vision of a swimming ammonite somewhat odd. From shell morphology differences with nautilus, the use of the “jet propulsion” method of swimming may not have been workable or efficient for ammonites.

In discussing the biology of the ammonites, some of these issues become even less clear. Monks and Palmer give some basic information for nautilus, squid, cuttlefish and octopus such as vision and feeding methods. It seems that the ammonites must have had a different feeding strategy than any of these modern predators. Fossilized stomach contents of ammonites (which in themselves are not certainly stomach contents) indicate they ate small slow moving animals.

One of the issues that has been worked out is that of sexual dimorphism. Many closely related species, differing primarily in size have now been determined to represent males and females of single species. Monks and Palmer indicate that the larger ones represent the females as is the case with many other animal groups.

Growth rate and life span of the ammonites is yet another area for conjecture. Based upon ammonite habitats as warm shallow seas, it is believed that they probably grew faster than the modern nautilus making them more like squid and cuttlefish. Even at this, Monks and Palmer report of a study that projected life span of one ammonite at 36 years making it more like the long lived nautilus. This study was based upon known growth rate for an epifaunal worm on an ammonite shell. Another study based upon isotopic analysis of the shell of a small ammonite indicated that it had lived through 12 seasonal changes.

The next to last chapter of Ammonites involves taxonomy and classification. Here the reader will learn that Monks and Palmer have used the term “ammonite” in its somewhat generic and popular sense. More correctly the book is about ammonoids of which only one order of nine are the true ammonites. Be that as it may, this final chapter gives general descriptions of each of these nine orders. Some of this descriptive information is morphologic and some is biologic. The included glossary is helpful for some of the terms used in this chapter.

Monks and Palmer wrap up with a chapter on the extinction of the ammonites. Each of the orders introduced in the preceding chapter became extinct at different times. As with many extinction related events through geologic time, these are no different in that they have mysterious and little understood causes. Monks and Palmer maintain that the ammonites may be more closely allied with coleoids (squids, cuttlefish and octopus) than with the modern nautilus making their ultimate demise that much more strange.

Readability: High School level and above. The few technical terms used are defined in context or covered in the glossary.

On the Upside: Nicely illustrated and very readable with the most current information on the ammonites.

On the Downside: Outrageously expensive for the size of the book and the information contained within.

Overall Rating: Ammonites is a good book about one of the most popular of the invertebrate fossils and a valuable book for the ammonite enthusiast. I can’t rate Ammonites as excellent because of the cost – it does little good to write a book for the general reader if it is priced such that most people won’t be able to afford it.

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