As one of the reviewers of the original manuscript I early declared my interest in this work, and indirectly I also had the opportunity to guide and support the progress of getting it published. Therefore, it comes rather naturally to say that I am pleased to see this work published after all the effort I know was put into it, not forgetting the great scientific value it provides.

Thelodonts, which are the main focus of this work, are an ensemble of fossil jawless vertebrates distinguished from other jawless vertebrates by the organization of their exoskeleton which is entirely made up by minute scales that resemble the placoid scales of sharks. Most studies on thelodonts have been based on isolated scales only, but more recent studies on articulated thelodonts have shown that simple scale taxonomy can be misleading because of the wide range of scale morphologies that can occur in the same individual. Some scientists, including the authors of this monograph, have instead used articulated specimens to establish a more stable taxonomic approach, and have provided a model for how a set of scales in a ‘microvertebrate’ assemblage can be used to recognize taxa that better represent a species. This approach, obviously, gives a more accurate account for taxonomic diversity. However, articulated specimens are rare and the difficulties in understanding the fossil record have hampered accurate estimations of general diversity and potential radiation events, despite the fact that isolated scales of thelodonts for a long time have been regarded as very useful tools in biostratigraphy.

The present monograph, which is primarily a taxonomic study, provides a large amount of new data based on material yielding 39 thelodont species from the Canadian Arctic Archipelago, of which 12 are based on articulated material. Using this new information, Märss and her co-authors have been able to revise thelodont systematics and minimized many of the taxonomic problems that have followed this research for some years.

The accumulated knowledge from previous work in general and this work in particular shows that both taxonomic and morphological diversity of thelodonts is much greater than previously believed. This new information can and will be used both in a phylogenetic context and greatly to improve biostratigraphical resolution.

Beside its systematic value, this well illustrated volume clearly demonstrates, using the articulated material, the morphological variability of scales in one individual and how that can be used for ‘microvertebrate’ assemblages. In this context, this monograph is also of educational value and interest for a broader readership of geologist, palaeobiologists and students, and not only the more obvious readers such as specialists on early fishes and biostratigraphy. It is however likely that the price of this volume (£54.00 paperback) will prevent the general category of readers from exploring this book for educational purposes, but for us specialists this is a much valued contribution.