Book Review: Cambrian Ocean World

Cambrian Ocean World: Ancient Sea Life of North America by John Foster (2014)

Cambrian Ocean World: Ancient Sea Life of North America by John Foster
The Cover of Cambrian Ocean World features a lovely painting by John Agnew that reconstructs Middle Cambrian time during deposition of the Spence Shale.

Cambrian Ocean World is a treasure trove of information, general and specific, for the trilobite enthusiast. Although the first fifty or so pages contain the obligatory general discussions/explanations of paleontological, geological, and biological concepts and terminology (and can likely be skipped by those with significant background in the earth and life sciences), the bulk of the book is a detailed march through the stratigraphy, depositional settings, and paleontology of the Cambrian section of North America–with minor digressions to places like Sirius Passet of Greenland.

In general, the book has a density of information similar to that of an undergraduate survey course textbook, and so it would be difficult to summarize its contents in detail. Below find a few snippets of commentary relating to some of the major features/interesting or unusual highlights contained within.

Modocia typicalis, Marjum Formation, Cambrian Period, Millard County, Utah
The elegant Modocia typicalis, Marjum Formation, late Middle Cambrian Epoch, Millard County, Utah. This book describes in some detail the depositional setting and fossils of the Marjum Formation, including the cyclic nature of its deposition. Sediments of the Marjum formation, along with those of many famous trilobite-bearing formations, were deposited along the northern margin of tropical Laurentia as shown in Figure 1.4B of the book. Specimen is 2.0 cm long.

Early in the book, a summary of the Precambrian history of the world includes a lengthy discussion the Ediacaran Period, its unique life forms, and the unresolved question of whether or not these organisms were true animals or represent an unrelated radiation of multicellular life before the dawn of the Cambrian Period. Another early point of interest in the book is a discussion of recently discovered moss spores in the Bright Angel Shale (of Grand Canyon section fame) and the notion that Cambrian terrestrial ecosystems may have also included algae, slime molds, and lichens–very different from the traditional view of the early Paleozoic landscape as being essentially barren.

The heart of the book begins with the appearance of Treptichnus pedum, a circular (in part) trace fossil of world-wide distribution and its preservation of the first complex burrowing/feeding behavior that marks the official beginning of the Cambrian Period. At this point in earth history, though, trilobites are still twenty million years in the future. The sudden appearance, fully formed, of the the oldest trilobites in North America, those of the Fritzaspis Zone of the Montezuma Range in Esmeralda County, Nevada, has led to speculation about soft-bodied trilobites or trilobite-ancestors extending back into the Proterozoic Era and other hypotheses of trilobite origins–ideas discussed by Foster.

Bolaspidella housensis, Wheeler Shale, Cambrian Period, Millard county, Utah
Cluster of Bolaspidella housensis, Wheeler Formation, Middle Cambrian Epoch, Millard county, Utah. The Wheeler Formation has been interpreted is a deep water, outer detrital belt unit deposited in a series of cycles reflecting sea-level rises and falls. Slab is 5.0 cm long.

Chapter 4 begins with an interesting discussion of Early Cambrian reefs. These reefs, composed primarily of archaeocyathids and other exotic organisms likely unrelated to extant reef-forming organisms, will be unfamiliar to most readers. The placement of trilobites in this exotic paleoenvironment is attention-getting and unexpected. Figure 4.3, for example, shows a Cruziana trace within this, what will be for most, weird paleoecological setting.

This middle part of the book also contains a somewhat lengthy discussion of trilobite morphology, taxonomy, stratigraphic distribution, and paleoecology. In addition to the typical discussion of the dorsal exoskeleton, the book explains trilobite nervous, digestive, circulatory, reproductive, and respiratory systems. Interestingly, the book references research suggesting that the outer branch of the trilobite limb (the filamentous branch), which traditionally has been considered a gill, rather was used to push water across the ventral surface for the purpose of respiration.

An important feature of the last half of the book is a series of descriptions of significant Cambrian fossil localities. Among many examples are localities in the Marble Mountains of California, Ruin Wash in the Pioche Shale of Nevada, and the House Range in Utah.

One chapter is devoted entirely to the Middle Cambrian Burgess Shale of British Columbia, a topic familiar to most trilobite enthusiasts. A highlight of the Burgess Shale chapter is a discussion of the functional morphology of the seven species of anomalocarids that occur in the Mount Stephen Trilobite Beds–and the lack of evidence that anomalocarids were the makers of “bite marks” in the dorsal exoskeletons of trilobites. Foster also touches on the potential role of submarine brine seeps in the paleoecology and preservation of fossils in the Burgess deposits. This is a topic not covered in most works for a general audience. Lovely stipple drawings of Burgess animals by Matt Celesky (reminiscent of those by Marianne Collins in Gould’s Wonderful Life) grace this part of the work.

Glyphaspis capella(?), Wolsey Shale, Bear Tooth Lake, Montana
An early asaphid: Glyphaspis capella(?), Wolsey Shale, Bear Tooth Lake, Montana. Like many groups of invertebrates, asaphid trilobites begin their adaptive radiation in the Middle Cambrian. Asaphids are important by the Late Cambrian and a major component of many Ordovician communities. They disappear near the end of the Silurian Period. Specimen is 2.2 cm long.

The concluding sections of the book focus on some technical aspects of paleobiology such as taphonomy, paleoecology, the nature of the Cambrian explosion itself, and the biological legacy of the Cambrian Period. This part of the book will likely challenge readers without significant formal background in paleontology, but are worth slugging though for the committed.

All in all, Cambrian Ocean World, is a wonderful source of information for anyone interested in the Paleozoic Era, even if it is used primarily as a reference and not read cover to cover. Having not worked in the geosciences for many years, this book reminds me just how much work, knowledge, and imagination is involved in trying to understand the fossil record and the life of the past. Foster’s book is certainly not for the vast majority who seek to skate around on the surface of existence, but for those seeking a fuller understanding of life on our planet it offers much to contemplate and appreciate.

@2017 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.

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