The Treatise on Invertebrate Paleontology, published from 1953–1966 by the Geological Society of America and the University of Kansas Press, 1969–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authored work of currently 55 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and extant (still living) invertebrate animals. The prehistoric invertebrates are described as to their taxonomy, morphology, paleoecology, stratigraphic and paleogeographic range. However, taxa with no fossil record whatsoever have just a very brief listing. Publication of the decades-long Treatise on Invertebrate Paleontology is a work-in-progress; and therefore it is not yet complete: For example, there is no volume yet published regarding the post-Paleozoic era caenogastropods (a molluscan group including the whelk and periwinkle). Furthermore, when needed, previously published volumes of the Treatise are revised.
Evolution of the project Raymond C. Moore, the project's founder and first editor, originally envisioned this Treatise on Invertebrate Paleontology as comprising just three large volumes, and totaling only three thousand pages. The Treatise project has expanded far beyond that original expectation. The project began with work on a few, mostly slim volumes in which a single senior specialist in a distinct field of invertebrate paleozoology would summarize one particular group. As a result, each publication became a comprehensive compilation of everything known at that time for each group. Examples of this stage of the project are Part G. Bryozoa, by Ray S. Bassler (the first volume, published in 1953), and Part P. Arthropoda Part 2, the Chelicerata by Alexander Petrunkevitch (1955/1956). Around 1959 or 1960, as more and larger invertebrate groups were being addressed, the incompleteness of the then-current state of affairs became apparent. So several senior editors of the Treatise started major research programs to fill in the evident gaps. Consequently, the succeeding volumes, while still maintaining the original format, began to change from being a set of single-authored compilations into being major research projects in their own right. Newer volumes had a committee and a chief editor for each volume, with yet other authors and researchers assigned particular sections. Museum collections that had not been previously described were studied; and sometimes new major taxonomic families—and even orders—had to be described. More attention was given to transitional fossils and evolutionary radiation—eventually producing a much-more complete encyclopedia of invertebrate paleontology. But even in the second set of volumes, the various taxa were still described and organized in a classical Linnaean sense. The more-recent volumes began to introduce phylogenetic and cladistic ideas, along with new developments and discoveries in fields such as biogeography, molecular phylogeny, paleobiology, and organic chemistry, so that the current edition of Brachiopoda (1997 to 2002) is classified according to a cladistic arrangement, with three subphyla and a large number of classes replacing the original two classes of Articulata and Inarticulata. All these discoveries led to revisions and additional volumes. Even those taxa already covered were expanded: Books such as those regarding the Cnidaria (Part F), the Brachiopoda (Part H) and the Trilobita (Part O) each went from one modest publication to three large volumes. The Porifera (Part E) revision resulted in five volumes while the Brachiopoda (Part H) revision concluded with six volumes.
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