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Journal of Paleontology

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Permian Hyolithida from Australia: The Last of the Hyoliths?

¹ Physical Science Department, San Diego City College, 1313 Park Boulevard, San Diego, CA 92101, <jmalinky@sbcglobal.net>

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

	INTRODUCTION

 
CLASS HYOLITHA Marek, 1963 encompassing the Order Hyolithida Sysoev, 1957 (Early Cambrian to Upper Permian) and Order Orthothecida Marek, 1966 (Early Cambrian to Early Devonian) consists of a group of conical, calcareous-shelled invertebrates of controversial affinity. One opponent view holds that hyoliths may be reasonably accommodated under the Phylum Mollusca (Malinky and Yochelson, 2007 and references therein), whereas another supports separate phylum status under the name Hyolitha (Pojeta, 1987 and references therein). Hyolith abundance and diversity attain a maximum in the Cambrian, followed by a progressive decline up to their Permian extinction (Fisher, 1962; Wills, 1993). Their demise was part of the extinction event of the Late Permian/Early Triassic. The cause(s) of this event remains controversial (Erwin et al., 2002), and no imprint remains in the geologic record of the specific circumstances surrounding the disappearance of the hyoliths, though it is highly probable that reduced population size was a contributing factor. Given the overall rarity of Late Paleozoic hyoliths, every occurrence is worthy of note to better understand patterns of hyolith diversity and abundance in the Late Paleozoic, the geographic and stratigraphic distribution of hyolith taxa and circumstances related to their extinction. The species from the Upper Permian described herein is among the youngest, if not the youngest, members of class Hyolitha.

All specimens are housed at the Natural History Museum (USNM), Smithsonian Institution, Washington, D.C.

	HYOLITHA IN THE PERMIAN

 
Hyoliths in the Late Paleozoic appear to have been rare components of normal marine, benthic invertebrate assemblages, and only nine species have been reported from the Permian (Morris in Strzelecki, 1845; Geinitz, 1861; Sinclair, 1946; Fisher, 1962; Gonzalez and Sabattini, 1972; Pagani et al., 2002). The species to which all specimens described herein were initially assigned, Theca lanceolatus Morris (in . . . [Full Text of this Article]