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Bivalved arthropods from the Middle Ordovician Winneshiek Lagerstätte, Iowa, USA

Published online by Cambridge University Press:  09 May 2016

Derek E.G. Briggs ,
Huaibao P. Liu ,
Robert M. McKay  and
Brian J. Witzke
Derek E.G. Briggs
Affiliation:
Department of Geology and Geophysics, and Yale Peabody Museum of Natural History, Yale University, PO Box 208109, New Haven, Connecticut 06511, USA 〈derek.briggs @yale.edu〉
Huaibao P. Liu
Affiliation:
Iowa Geological Survey, IIHR-Hydroscience and Engineering, University of Iowa, 340D Trowbridge Hall, Iowa City, Iowa 52242, USA 〈huaibao-liu@uiowa.edu〉 〈robert.mckay@uiowa.edu〉
Robert M. McKay
Affiliation:
Iowa Geological Survey, IIHR-Hydroscience and Engineering, University of Iowa, 340D Trowbridge Hall, Iowa City, Iowa 52242, USA 〈huaibao-liu@uiowa.edu〉 〈robert.mckay@uiowa.edu〉
Brian J. Witzke
Affiliation:
Department of Earth & Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, Iowa 52242, USA 〈brian-witzke@uiowa.edu〉
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Abstract

The Middle Ordovician (Darriwilian) Winneshiek Lagerstätte of northeast Iowa is preserved in a meteorite crater. Besides conodonts, the fossils are dominated by arthropods, particularly eurypterids and phyllocarids. Here we describe the bivalved forms, which include at least seven different taxa. The small phyllocarid Ceratiocaris winneshiekensis, new species, is the most abundant; it is the oldest representative of the Ceratiocarididae. A single incomplete abdomen and telson bearing furcal rami is reminiscent of notostracan branchiopods but its affinities are unknown. Decoracaris hildebrandi, new genus and species, is a rare form with a shield that extends anteriorly into a swollen horn and reaches lengths of 9 cm: it may represent a thylacocephalan crustacean but this cannot be confirmed without soft parts. Iosuperstes collisionis, new genus and species, is represented by suboval valves 10–25 mm long: its affinities are unknown. A probable leperditicopid, which ranges in length from 8 to 18 mm, is commonly preserved in a ‘butterflied’ configuration. It does not preserve the scars and sinuses characteristic of three-dimensionally preserved leperditicopids from elsewhere. Finally the fauna includes at least three ostracods, including a palaeocope with a granular surface and relief similar to Lomatopisthia, and a smooth ?podocope. The Winneshiek fauna differs from those of other Ordovician Lagerstätten from restricted settings such as Airport Cove and William Lake in Manitoba (Katian) where, apart from ostracods, bivalved arthropods are absent, and Silurian examples such as Brandon Bridge (Telychian), which lacks eurypterids, and the Williamsville Member of the Bertie Formation (Pridoli) where conodont assemblages are absent.

Type
Articles
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Journal of Paleontology , Volume 89 , Issue 6 , November 2015 , pp. 991 - 1006
Copyright
Copyright © 2016, The Paleontological Society 

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