Abstract

WAISFELD, Beatriz G  and  VACCARI, N. Emilio. THYSANOPYGE (TRILOBITA, EARLY ORDOVICIAN): SPECIES AND DISTRIBUTION IN THE NORTHWEST OF ARGENTINA. Ameghiniana [online]. 2008, vol.45, n.4, pp.753-774. ISSN 1851-8044.

The trilobite Thysanopyge Kayser is well-known for the great size it attained, and the distinct spinosity of the pygidium, an infrequent feature among asaphids. It is a widespread trilobite taxon in northwestern Argentina, ranging in age from late Tremadocian to Floian. The present revision, based on material from numerous localities, proposes criteria for the identification of species groups, mainly upon different designs of the cranidial anterior area, and the marginal pygidial spines. A reinterpretation of the type species, the classical Thysanopyge argentina Kayser, is proposed, providing new features for its identification. Complete morphological information on Thysanopyge clavijoi Harrington and Leanza, otherwise known from cranidia, is supplied. Two Thysanopyge species: T. frenguelli Harrington and T. taurinus (Harrington), previously considered synonymous with T. argentina, are recognized as distinct and valid species. In addition, two new species, T. victoriensis sp. nov. and T. maderensis sp. nov., are fully described and illustrated. Two distinct morphotypes are recognized based upon different overall size ranges, proportions of exoskelentons, and pygidial design. Thysanopyge largely flourished in muddy substrates. Distribution of morphotypes and compostion and diversity of associated assemblages appear to be related to variation in oxygen levels, from well-oxygenated to dysoxic bottom waters.

Keywords : Thysanopyge; Trilobita; Ordovician; Northwestern Argentina.