Paper No. 39-0
VARIATION IN THE GENUS SPINATRYPA (BRACHIOPODA, ATRYPIDINA): TERATOLOGY, HYPERTROPHISM OR SPECIATION?
ROSSBACH, Thomas J., Department of Geological, Environmental and Marine Sciences, Elizabeth City State University, Elizabeth City, NC 27909, tjrossbach@mail.ecsu.edu.

The brachiopod genus Spinatrypa Stainbrook, 1951, is abundant in Upper Devonian rocks of the Appalachian basin. It is easily recognizable and is biostratigraphically important as its disappearance is taken as a marker for the Late Devonian Frasnian-Famennian extinction event. Two species are common, Spinatrypa spinosa (Hall, 1843) and Spinatrypa hystrix (Hall, 1843). Recent investigations have revealed unusual variations in S. hystrix close to the Frasnian-Famennian boundary. The variations include an increase in overall size, a change from a circular to a distinctly triangular valve shape, and the presence of a distinct fold and sulcus not seen in typical forms.

This morphology has so far only been seen within a small interval of the Blizzard Member of the Foreknobs Formation. The Blizzard Member is known for the abundance and diversity of its fossils, however these forms appear to be unique. The unusual morphology could be the result of one of three factors. First, they could represent teratological specimens (biological monstrosities) of S. hystrix. Second, they could represent hypertrophic forms of S. hystrix (results of excessive growth sometimes seen in optimal ecological conditions). Third, they could represent a distinct new species directly descended from S. hystrix. The first two scenarios would provide little biostratigraphic information since the variation is very localized. The third possibility is more intriguing. It would imply a very short-lived species (probably less than 100,000 years) which itself became extinct before the other atrypids. The apparent endemic nature of the new morphology may restrict its biostratigraphic usefulness, but it may also signify the last speciation of Spinatrypa in the Appalachian basin prior to the termination of the lineage during the Frasnian-Famennian extinction.

North-Central Section (36th) and Southeastern Section (51st), GSA Joint Annual Meeting (April 35, 2002)
Session No. 39--Booth# 10
Paleontology (Posters)
Heritage Hall: East
8:00 AM-12:00 PM, Friday, April 5, 2002
 

© Copyright 2002 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.