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Journal of Paleontology

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THE SYSTEMATICS AND ONTOGENY OF PYRGOPOSTIBULLA BELLI, A NEW EDRIOASTEROID (ECHINODERMATA) FROM THE LOWER DEVONIAN OF NEW YORK

¹ Department of Earth and Planetary Sciences, University of Tennessee, Knoxville 37996-1410, <csumrall@utk.edu>,
² Department of Geology, University of Cincinnati, Ohio 45221-0013,
³ Department of Geology, St. Lawrence University, Brown Hall, Canton, New York 13617-1410

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
POSTIBULLINID EDRIOASTEROIDS are a small clade of discoidal edrioasteroids that are locally common members of Devonian to Pennsylvanian, shallow marine, hard substrate faunas in North America and Europe. A small discoidal theca, narrow, highly elevated ambulacral cover plates, a highly elevated anal pyramid, and in many forms a posterior oral protuberance characterize this clade (Bell, 1976b; Sumrall et al., 2000). Here we describe the oldest known postibullinid, Pyrgopostibulla belli n. gen. and sp., a species that differs from other postibullinids by having a well-developed pedunculate zone and a complex, five-plate pattern of ambulacral cover plates. A dense population of these edrioasteroids preserved at a single stratigraphic horizon provides a census sample of individuals that were killed as a part of a final and abrupt burial pulse on this Lower Devonian hardground (Cornell et al., 2003). As such, this case study provides insight into the ontogeny and colonization strategies of isorophinid edrioasteroids.

	OCCURRENCE AND TAPHONOMY OF PYRGOPOSTIBULLA BELLI N. GEN. AND SP

 
Stratigraphy and geological setting
The hardground bearing Pyrgopostibulla belli occurs in the lower submember of the Thacher Member of the Manlius Formation. The Thacher Member comprises the lowest unit of the Lower Devonian Helderberg Group (Fig. 1). While there has been some controversy concerning the exact age of the Thacher Member (see Matteson et al., 1996), most workers accept this unit is of Earliest Devonian (Lochkovian) age based on conodonts (Rickard, 1975). The Thacher Member represents the initial portion of a marine transgression, superimposed on the final phases of the Tippecanoe (Tutelo Phase) Megasequence (Sloss, 1963). In eastern New York State, the Thacher Member is composed mainly of shallow water "ribbon" limestones (dark blue-gray, fine-grained calcisiltite); a number of hardgrounds occur on the upper surfaces of these beds. The edrioasteroid-bearing hardground occurs near the top of a small-scale shallowing-upward cycle, . . . [Full Text of this Article]

This article has been cited by other articles:

				C. D. SUMRALL, C. E. BRETT, and M. L. McKINNEY A NEW AGELACRINITID EDRIOASTEROID ATTACHED TO A LARGE HARDGROUND CLAST FROM THE MCKENZIE MEMBER OF THE MIFFLINTOWN MEMBER (SILURIAN) OF PENNSYLVANIA Journal of Paleontology, September 1, 2009; 83(5): 794 - 803. [Abstract] [Full Text] [PDF]