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Late Paleozoic Pelecypods: Pectinacea

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Late Paleozoic Pelecypods: Pectinacea

by Norman D. Newell

Cover of the book; dark blue cloth with gold imprinting of title on binding.

Originally published in 1937 as University Geological Survey of Kansas Volume 10, Part 1. This is, in general, the original text as published. The information has not been updated. An Acrobat PDF version (48 MB) is also available, with the plates in a separate volume (14 MB).


by Raymond C. Moore

Kansas is fortunate in having an abundance of well-preserved fossils. These remains of once-existing animals and plants, buried in rock, are by no means mere objects of curiosity, popular or scientific. Interest in them is not confined to the evidence that they yield of great geographic changes which the region, now called Kansas, has witnessed during its geologic history—ancient swamps choked with subtropical types of plant growth where now is grassy plain, widespread salt-water seas where now is high, dry ground, and many other contrasting environments. Many of the vanished animals and plants of Kansas, represented by the fossils, are sufficiently like living forms to cause wonder that so little change should have occurred between ancestors and descendants in 100 million years, or, referring to fossils of eastern Kansas rock formations, in more than 200 million years. Many of the known former inhabitants of this region, on the other hand, are so unlike any animals or plants of the modern world that they would seem not to belong to this planet if interconnecting types of life were not also known from the fossil record. But in the minds of matter-of-fact citizens of "practical" bent, these observations have only academic interest; they have no application to affairs of commerce. Such a conclusion is largely erroneous.

Study of fossils—paleontology—has direct practical value as applied to identification of the rock strata from which the fossils were obtained. It is particularly true of geologic investigations in Kansas that careful observations of the distribution and nature of certain kinds of fossils have much use in strictly economic work—investigations having as their object the development of mineral deposits useful to man. This use of fossils is more or less restricted to application in the hands of the trained geologist, but it is none the less important on this account. In many instances the "layman" or amateur geologist is able to make practical use of observations and study of fossils, without considering so-called cultural interests. The uses that are of economic significance, here considered, are dependent primarily on the fact that the kinds, or species, of fossils and the associations of groups of fossils of certain kinds are restricted in occurrence to particular rock layers. The fossils are somewhat like labels, and there are different "labels" or combinations of "labels" for different rock strata. Because many fossils superficially resemble one another closely, or are actually so closely alike that discrimination is difficult, good illustrations and careful descriptions prepared by an able specialist in this branch of geologic study are needful. Publication of the results of paleontologic research makes generally available knowledge that otherwise could be utilized only by the geologist who made the painstaking study for himself.

Critical investigations of Kansas fossils have constituted only a rather small part of the activities of the State Geological Survey, although large use has been made of paleontologic observations in conducting certain field work pertaining to general or economic geology. It is evident that research in this field should be supported, however, because, as already indicated, the results are practically useful in work on geological problems of Kansas; also, it is apparent that as regards the Upper Carboniferous (Pennsylvanian) and Permian rocks of eastern Kansas, and to some extent the Cretaceous and Tertiary deposits of western Kansas, the geologic section of Kansas is fitted to serve as a standard for comparison in studies of other parts of North America and of other continents. Thus, paleontologic studies in Kansas have extremely wide application.

Experience indicates that among different methods of paleontologic study, that illustrated by the present work is most valuable. Here we have a certain group of fossils that is closely related biologically; representatives of this group from all rock strata where they are known, but especially Kansas and adjoining territory, are brought together; critical comparative study of form and structure of these fossils, with special reference to their geologic occurrence, is best fitted to bring out significant features in identification and use of the fossils. This type of investigation, best suited to define biologic distinctions, lacks consideration of the natural association of fossils to form assemblages called faunas, in the case of animals, and floras, in the case of plants. This latter study is also significant, but it cannot be made very satisfactorily until the biologic discriminations within each class of organisms have been established. Much of the older paleontologic work in Kansas had the defect that insufficient comparative study of similar groups of fossil organisms from precisely known geologic horizons was provided; hence, various kinds (species) of animals or plants that are actually distinct were grouped together, and in some cases forms that seemed different now appear to have been separated on merely superficial dissimilarities.

The following report by Doctor Newell covers one group of shells belonging to the class called Pelecypoda. These are two-shelled invertebrates that are represented by the very abundant, highly varied clams of marine waters and by the mussels of fresh-water streams and lakes. Pelecypods are very numerous as fossils in many rock formations of Kansas, but they have never been exhaustively studied. It is reasonably certain that fuller knowledge of these shells will make them much more useful in practical geologic work, and this is greatly to be desired since the pelecypods are so common. This volume deals with the "scallops" or Pecten-like forms, and is the first of a number of projected reports dealing with the late Paleozoic pelecypods, based mainly on the large collections of fossils from Kansas and adjacent states of the northern Mid-Continent region of the United States.

To date no comprehensive study of the American Late Paleozoic pelecypods has appeared. The many species known from rocks of Pennsylvanian and Permian age have been described in various publications, but the descriptions commonly were incidental to general faunal studies. Many of the original descriptions are inadequate, and are accompanied by poor illustrations or none at all. There has been much confusion regarding the precise nature or a great many pelecypod species; consequently these species have been variously interpreted by paleontologists. In many instances it is impossible to discover the true characters of a species without recourse to the type specimens, because the descriptions of a large proportion of the Pennsylvanian and Permian species are so generalized as to embrace many similar, but nevertheless distinct, forms. Unfortunately, some of the types described by the early paleontologists have been destroyed or lost, and in instances in which the exact locality and horizon from which the original specimens came is unknown, it is often impossible to determine to which of several species a particular name should be applied.

Modern technique for investigating internal characters of fossil shells has not been in general use. Consequently, few paleontologists have been able to give satisfactory descriptions of Late Paleozoic pelecypods. It is not surprising, then, that the shell interior of many pelecypod species and genera is still unknown. The microscope, now considered as essential equipment of the paleontologist, has been used only too infrequently in past studies of pelecypod shells, with the result that one whole line of evidence for classification has been neglected—that of shell microstructure.

The work of two men, F. B. Meek and G. H. Girty, in Pennsylvanian and Permian pelecypods indisputably stands above the work of all other American authors. Girty's descriptions are particularly satisfactory because of the high quality of the illustrations accompanying them.

The pelecypods of the Upper Paleozoic rocks of the Mid-Continent region, including Texas, Oklahoma, Kansas, Missouri, Nebraska, and Iowa, in many cases are well preserved and locally are very abundant. Although this class of Mollusca has been of little use in the past for stratigraphic correlation in the Upper Paleozoic rocks, there is reason to believe that certain groups of the pelecypods eventually will be comparable to the fusulinids, brachiopods, and gastropods as useful index fossils.

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Kansas Geological Survey, Geology
Placed on web Dec. 1, 2017; originally published 1937.
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