Some Typical Upper Eogene Fish Scales from California

Abstract

Fossil fish scales belonging to 16 families and to 18 genera from the California Eogene are described in this paper. The majority of the scales come from cores of the Kreyenhagen formation penetrated in oil wells of the San Joaquin Valley. In general, fish scales are plentiful in these strata, whereas there is a sparsity of such remains in the Middle and Lower Eocene. The fossil specimens come from localities rather widely distributed, but not all occurrences of the Kreyenhagen shale have been sampled for scales. The collection shows great uniformity, so far as abundance of the more typical forms is concerned. It is certain that the important and characteristic fish types of Kreyenhagen age are well represented. The assemblage of scales does, however, contain a number of forms that are rare and too fragmentary to warrant description. Unquestionably, still other types will be found in regions not yet explored for this kind of material. Special attention has been paid to scales of Upper Eocene age. Many of these, however, range in occurrence into the Oligocene. The Kreyenhagen formation, for example, which furnished most of the material, includes at its type locality rocks of Oligocene and Upper Eocene age (Jenkins, 1931, pp. 142-143). The present paper is concerned only with the Oligocene and Upper Eocene parts of the wells that were the sources of the fossil material. The age of the fauna is stated to be Upper Eogene rather than Upper Eocene and Oligocene, since the treatment of the Oligocene assemblages is very incomplete, and rocks of this age are represented by only thin sections in the region. A number of new genera and species are established on the basis of scales, since the characters of these structures differ more or less markedly from those of any known form, living or extinct. It must be pointed out that in most instances the fishes to which the scales belong are not known, and the taxonomic position of the genera is frequently doubtful. Diagnoses of the genera have therefore not been given. It seems desirable not to present these diagnoses until such time as the scales and their classification are better known. The genotype species is the only one described for each of the new genera recognized in this paper. Species are described as fully as possible.

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