Journal of Paleontology, Vol. 16, No. 6, pp. 764-776, 9 text figs., November, 1942 



OCCURRENCE AND STRATIGRAPHIC DISTRIBUTION 

 OF PALEOZOIC OSTRACODES^ 



CHALMER L. COOPERS 



Abstract. — Although the Ostracoda constitute one of the most persistent orders 

 of microfossils (Lower Ordovician to Recent) they are, considered in detail, quite 

 diversified in character. While many genera are extremely long lived, careful study 

 of formational materials reveals many species that are of value as index fossils. 

 Ostracodes have been found in all types of marine sediments throughout most of 

 the Paleozoic. The differentiation of fresh water forms becomes marked with the 

 initiation of sedimentary conditions which resulted in the rapid alteration of fresh 

 water and marine beds in the sedimentary cycles of the Pennsylvanian and Permian. 



INTRODUCTION 



SINCE THE segregation of the crustacean 

 "Ostrachoda" as an order by Latreille 

 (1801), these forms have become, next to the 

 Foraminifera, the best known group of mi- 

 crofossils. Study of these fossils during the 

 last 140 years has given us almost 3400 spe- 

 cies from the Paleozoic, classified into about 

 300 genera. The ostracode literature would 

 form a good sized library of about 800 titles. 

 However, more than 50 years were required 

 to produce the first 50 titles, after which a 

 rather steady production of about 10 papers 

 per year was maintained (see fig. 1). 



Little progress was made until Jones and 

 his associates Kirkby and Brady began their 

 intensive studies in Great Britain about the 

 middle of the nineteenth century. Their work 

 stimulated others, particularly on the Con- 

 tinent and in North America. Ulrich in 1890, 

 1891, and 1900 published papers on the 

 "New and little known Paleozoic Ostra- 

 coda," and Ulrich and Bassler published 

 their "New American Paleozoic Ostracoda" 

 in 1906 and 1908. In 1923 their "Morphol- 

 ogy, Classification and Occurrence" together 

 with the systematic treatment of the Clin- 

 ton ostracodes of Maryland appeared. This 

 was the most careful and comprehensive 

 stratigraphic treatment based on the ostra- 

 codes yet to appear, and it will probably 

 long remain preeminent in this field. Nine 

 zones, each characterized by the prolific and 

 persistent occurrence of an ostracode spe- 



^ Presented at the conference of the Research 

 Committee on Sedimentation, at the 27th Annual 

 Meeting of the Am. Assoc. Petroleum Geolo- 

 gists, Denver, April 21, 1942. 



2 Illinois State Geological Survey, Published 

 with permission of the Chief. 



cies, were recognized in this Niagaran for- 

 mation of western Maryland and adjacent 

 parts of Pennsylvania. Work on ostracodes 

 received further stimulation in this country 

 during the last two decades due to the in- 

 creasing importance of micropaleontology in 

 petroleum geology. The excellent bibliogra- 

 phy of Bassler and Kellett (1934) is indis- 

 pensable to any worker in Paleozoic ostra- 

 codes. Since the publication of this very 

 comprehensive work 167 genera and about 

 900 species have been proposed in 91 papers 

 (Agnew, 1942). 



The systematics of the order has in no 

 manner kept pace with the number of new 

 forms described. Since Latrielle divided the 

 Crustacea into two subclasses and included 

 the Ostracoda under the Entomostraca a 

 number of writers have dealt with the classi- 

 fication of these fossils. In 1850 Baird gave a 

 general description which has served to dis- 

 tinguish the order until today. Dana, in the 

 various editions of his "Manual of Geology" 

 gave a general classification which was 

 rather commonly followed from 1863 to near 

 the end of the century. In 1889, Brady and 

 Norman gave a detailed classification. Bass- 

 ler (1913) in Zittel's "Textbook of Paleon- 

 tology" divided the Eucrustacea into five 

 superorders, and the Ostracoda (the third) 

 into nine families. Later Ulrich and Bassler 

 (1923) divided the Ostracoda into 3 super- 

 families, 19 families, and 130 genera, several 

 of which are not represented in the Paleo- 

 zoic. In 1934 (Bassler and Kellett) this 

 number had grown to 18 families and 198 

 genera for the Paleozoic only, and in the lat- 

 est compilation the figures show, not count- 

 ing those eliminated by synonomy, 30 fami- 

 lies and 310 genera. Those who have made 

 recent contributions to the classification are 



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