From the coordinating author's preface:
"This Second Revision of the Part V Treatise on Invertebrate Paleontology, dealing with the phylum Hemichordata, is a considerably extended version of the Graptolite Treatises of Bulman (1955, 1970), which primarily covered the Graptolithina, at the time interpreted as an extinct class of the Hemichordata. With the recognition of the Graptolithina as fossil members of the Pterobranchia and the identification of the benthic colonial pterobranch Rhabdopleura as an extant graptolite (Mitchell & others, 2013), the focus in this volume is extended to include the record of fossil Hemichordata and to also examine the soft-body anatomy in more detail. Zooidal anatomy is important for the interpretation of the fossil graptolites and their life style and points to the importance of modern biology in understanding the fossil record. The two editions of Bulman's Treatise (1955, 1970) have been the standard for graptolite research for seven decades, but their precursor in the Handbuch der Palaozoologie (Bulman, 1938) seems to be nearly forgotten and is difficult to obtain. This volume could be regarded as the first version of the Graptolite Treatise, because it covers in a similar manner all the main aspects of graptolite taxonomy and its understanding at the time of publication and was obviously the basic source for the later versions. Unfortunately, it was published at the wrong time and in the wrong country. Bulman (1938) established all the basic taxonomic concepts in the volume, even introducing a number of new taxa.
Bulman's work on the graptolites and their taxonomy in the two previous Treatise volumes is neither the only one nor the first attempt at a general overview of graptolites. However, most general treatments did not attain the influence and acceptance in the international scientific community, either due to the language in which they were published or the time of publication. Hall (1868) and Frech (1897) provided an understanding of graptolite research during their times and achieved important and valuable insights. General overviews by Dawydoff (1948), Waterlot (1953), Munch (1952), Mu and Lee (1960), and Obut (1957, 1964) had less impact due to the language barriers (published in French, German, Chinese, and Russian, respectively), but nevertheless they were important in shaping the opinions of generations of researchers.
Discussions to produce a new Graptolite Treatise began more than 20 years ago, with Chuck Mitchell and Mike Melchin initiating the first steps with then Treatise Editor Roger Kaessler. Along the way, there were meetings in Prague (1999, 2008), Nanjing (2007), and Sardinia (2009). Twelve years into the project, Jörg Maletz became Coordinating Author when Chuck Mitchell was unable to continue due to other commitments. He began producing a newsletter in 2010 to track progress and keep in touch with authors.
Scope of the volume: This volume is aimed at providing the most complete and up-to-date information on the fossil Hemichordata, their taxonomy, and their use in the geological sciences. The inclusion of not only the Pterobranchia (Graptolithina) but also the Enteropneusta shows our increased knowledge of the relationships of this fascinating fossil group with extant groups of organisms. This approach connects the fossil graptolites with their closest relatives, largely known from extant organisms.
Graptolites, the main focus of this volume, have been used successfully in the understanding of lithostratigraphic successions, unraveling structural complexities in geology and, thus, are important biological objects enabling numerous geological interpretations, as detailed on p. 127-134 (first published as Maletz & Vandenberg, 2021, Treatise Online). Lapworth (1878) first used graptolites to decipher the tectonic complexities in the succession of the Moffat Series, a milestone in graptolite research (Fortey, 1993; Hamilton, 2001) and a first hint on the importance of graptolite research to applied geology. Graptolite fusellum has been used to determine temperature and burial histories of Paleozoic sediments (e.g., Goodarzi & Norford, 1985). Graptolite research, thus, goes far beyond the identification of taxa and the relative dating of successions that included graptolites as index fossils. It is not just a discipline for taxonomists and fossil collectors; the geological application of graptolites is still developing and modern data collection and database interpretations may infuse new life into graptolite research. In recent years, paleodiversity studies using graptolite faunas have become the focus of research on extinction and origination intervals in Earth's history (e.g., Crampton & others, 2020).
The Enteropneusta, unfortunately, have been neglected in the past because so few fossil ones were recognized, and even the extant enteropneusts were rarely investigated in much detail. Only through the renewed interest in the Burgess Shale biota and their preservation, fossil Enteropneusta have gained more interest. As a result, new fossil taxa have been studied and described, including ones that are tubicolous (e.g., Caron, Conway Morris, & Cameron, 2013; Nanglu, Conway Morris, & Cameron, 2016; Cameron, 2018) and one with tentaculate arms (Nanglu, Caron, & Cameron, 2020), two characteristics that were previously regarded as restricted to the Pterobranchia.
Additional information: Colour versions of many of the specimens and illustrations in this volume are available in Treatise Online. A reference to a colour version is included in captions when colour contributes vital information. The systematic description section, which begins on p. 189, also includes additional introductory information and morphology details for each taxon group."