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Proceedings of the Iowa Academy of Science Volume 84 Number Article 4 1977 Praepholidocidaris, a New Echinoid from the Pella Formation (Mississippian) of Iowa T. J. Frest University of Iowa H. L. Strimple University of Iowa Let us know how access to this document benefits ouy Copyright ©1977 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Frest, T. J. and Strimple, H. L. (1977) "Praepholidocidaris, a New Echinoid from the Pella Formation (Mississippian) of Iowa," Proceedings of the Iowa Academy of Science, 84(3), 98-105. Available at: https://scholarworks.uni.edu/pias/vol84/iss3/4 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact [email protected]. Frest and Strimple: Praepholidocidaris, a New Echinoid from the Pella Formation (Miss 98 Praepholidocidaris, a New Echinoid from the Pella Formation (Mississippian) of Iowa T. J. FREST and H. L. STRIMPLE 1 FREST, T. J. and H. L. STRIMPLE (Department of Geology , The University adradial plate columns. Age relati onships of the Pell a Formation and the of Iow a, Iowa City, Iowa 52242). Praepholidocidaris, a new Echinoid from the paleoecology of it s echinoderm fa una are reviewed . It is concluded that the Pella Formation (Mi ssissippian) of Iowa . echinoderms represent an opportunistic assemblage and the bulk of the Praepholidocidaris pellaensis, n. gen., n. sp., is described from basal Chester­ echinoderm fa una support s assignment of unit C of the fo rmation to the Talaro­ ian rocks in the vicinity of Oskaloosa and Gi vin , Mahaska County, Iowa. The crinus Zone (of Horowitz and Strimple, 1974 ), basal Chesteri an. new genus is characteri zed by its small number of ambulacral and interambulac­ INDEX D ESCRIPTORS: Late Mi ssissippian; Chesterian; Ta larocrinus Zone; ral plate columns, adorall y expanded ambulacra, unequal ambulacrals with Pell a Formati on; Mahaska Count y, Iowa; Echinodermata; Echinoidea; perforate primary spines, and interambulacrals with primary spines only on Echinocystitidae; Praepholidocidaris pellaensis; Pholidocidaris ; paleoecol­ ogy. The prolificall y foss ili fe rous Mississ ippian Pella Formati on has been substrates for those species which were sessile. There is little deviation a subject of paleontological investigations for more than a century from typical abundance of these groups in the echinoderm layer (in fact (Hall , 1858). However relatively little modem work has been done on some are commoner th an at other levels); however hold fas ts and the the invertebrates, and some groups have been almost totally neglected. certainly sessile edrioasteroids are more than usuall y common, but are This is particularly true of the Ec hinodermata: though long known as a still rather rare as compared to the number of crown s recovered. The so urce of exceptionally preserved bl astoids other echinoderm classes lithology of the echinoderm zone, rarity of many- pl ated camerates(e.g. wi th the exception of the Edrioasteroidea (Strimple, 1968; Bell , 1976) Batocrinus), abundance of flexibles, and presence of free-li ving genera and two crinoids (Strimple, 1974) have not been previously re ported. such as Camptocrinus indicate that the echinoderm s were either Collecting in recent years has yielded a variety of crinoids, edri oas­ broadl y tolerant species or were adapted to soft bottoms. The latter teroids, and starfish as well as the echinoid described below: these will alternati ve is most probable: the commonest edri oasteroid (Lepidodis­ be the subject of future report s. Unlike the rather ubiquitous bl astoids cus laudoni; see Bell , 1976 , pp. 557-567) has a claveate theca with the (Pentremites conoideus, Diploblastus glaber ) nearl y all of the other oral face in the adult elevated considerably above the original point of echinoderm s have been fo und onl y at a single locality, the abandoned attachment of the theca. It seems likely that the majority of the Pell a county quarry , north of Oskaloosa, Iowa, although a single echinoid crinoids, as we ll as the echinoid and starfis h, were effectively was collected at the Banzee quarry, near Givin , Iowa (detailed eleutherozoic ( sensu Kirk , 19 11 ) due to the nature of the substrate and localities cited below). Most of the echinoderms are restricted to a probable comparatively high rate of sediment acc umulation. si ngle thin layer in the upper third of the formati on. None of the Precise age relati onships of the Pell a are uncertain. The hi story of the echinoids were fo und in pl ace though crinoids and blastoids have been fo rmation has been reviewed by Rexroad and Furni sh ( 1964 ), who also recovered in situ . The majority of specimens are loose on dump piles provide a secti on of the Oskaloosa exposure (their text-figure I). On the where shale discarded from the echinoderm-bearing layer happened to basis of the conodont fa una these authors place the fo rm ation within the have been the last materi al discarded: hence the distribution of the Gnathodus bilineatus - Cavusgnathus characta Assemblage Zone and echinoderm s as coll ected is extremely spotty. correlate it with the Ste. Genevieve (Rexroad and Furnish, p. 669). Most of the crinoids occur as crown s, often retaining part of the Series assignment of the Ste . Genevieve has been either to the Merame­ column , despite the poorly indurated nature of the enclosing rock, can , the Yalmeyeran, a separate series between the Yalmeyeran and which in pl aces approaches a mudstone. Many bl astoids retain the Chesterian (e.g . Swann , 1963), or the Chesterian. On thi s po in t Rex­ brachi oles and covering pl ates, and several of the echinoid s and starfish road and Fumish(op. cit.) comment that ' 'the Ste . Genevieve conodont have spines still articul ated , probably indicating an autochthonous fa una is sharply different from the conodonts of the underl ying fo rma­ assemblage. In most echinoids the interambulacral plates have shifted tions of the Valmeyer series but is closely simil ar to, if not ident ical and become telescoped or are otherwise disrupted; this is likely due to with, the conodont s of the overl ying Chester series" (p . 669). Wi th sediment compacti on aro und origin all y intact specimens. The crinoid regard to the Pell a echinoderm zone (included in unit C of Rexroad and fa una is peculi ar in th at it is dominated in terms of abundance by the Furnish, op. cit .) we prefer the Chesteri an assignment fo r the forma­ flexible Taxocrinus shumardianus whereas the majority of species are tion. Talarocrin us, a common constituent of Chesteri an fa un as, is in adunate s. The camerates are mostl y simple types (Dichocrinus, present in the Pell a while Platycrinites appears to be unrepresented Camptocrinus, Talarocrinus). For many crinoid species fe w adult or even by stems. ve ry yo ung indi viduals are encountered, and most (e xcluding the fl exi ­ Other echinoderm s present in the Pell a (i.e. Taxocrinus shumar­ bles) have not been recovered even as isolated plates outside of the dianus, Diploblastus glaber) could support ei ther a Late Meramecan or echinoderm zone though Praepholidocidaris, blastoids, edrioas­ Early Chesteri an age fo r the top of the fo rmati on. On the whole the teroids, and stems do occur at other levels in the Pella. The fauna seems preponderance of species indicates the likelihood of Early Chesteri an to represent an opportunisti c assemblage that was able to populate a age (Talarocrinus Zone as defin ed by Horowitz and Strimple, op. cit ., small area of the Pella-age sea bottom for an extremely short period of pp. 207 , 213) for unit C of the Pella. time, perhaps during an interval of slightly decreased sedimentation , but was abruptly wiped out by an influx of mud. Sedimentation rate was PALEOECOLOG Y most likely the determinant factor in establishing fauna) composition and in the eventual terminati on of the assemblage since other inverte­ Praepholidocidaris (new genus) was an integral member of the Pella brates, especiall y brachiopods and corals, could have provided hard echinoderm fauna. Despite the generally fragil e nature of echinoid tests it is represented by over thirty specimens. The occurrence is unusual in !Geology Department , The University of Iowa, Iowa City, Iowa, 52242. that the echinoids were not fo und in a· ' nest' ' but are scattered sparsely Published by UNI ScholarWorks, 1977 1 Proceedings of the Iowa Academy of Science, Vol. 84 [1977], No. 3, Art. 4 A NEW ECHINOID FROM IOWA 99 throughout the echinoderm-bearing layer. Other echinoids are virtually this paper relate to these three species collectively. absent: a few plates and spines of an archaeocidarid were the only other The finding of a genus which when dissociated would yield plates echinoid remains encountered despite intensive search. The seeming and spines virtually indistinguishable from those of Pholidocidaris paucity of echinoid species supports the inference of an opportunistic suggests that the acription of such material to a definite genus, as was assemblage. Praepholidocidaris seems to have been more tolerant of commonly done in the past, is unjustified unless a very large number of silty conditions than many of the Pella species: isolated plates and isolated parts, allowing a virtual reconstruction in full, is available. spines have been observed at other levels in the Pella and as mentioned This point has been made previously by Kier ( 1958, p. 11) in connec­ above it is one of the few species to be found outside of the Oskaloosa tion with the Archaeocidaridae.

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