Lower Devonian aulacopleurids trilobites from Argentina

RUSTÁN, JUAN JOSÉ

Toledo, España

Conferencia; Fouth International Trilobite Conference (Trilo08); 2008

INTRODUCTION Aulacopleurids are widespread, frequent and diverse elements with long stratigraphic ranges (Ordovician-Devonian) out of the Malvinokaffric Realm. Nevertheless, their Malvinokaffric record almost exclusively restricted to the Devonian, is scattered and of low diversity. Due to this particularity and, probably, to the fragmentary nature of the type material, and the lack of proper illustrations and detailed studies, the only two genera recognized (Malimanaspis Baldis and Longobucco, 1977 and Maurotarion Alberti, 1969) (Adrain and Edgecombe, 1996), have received secondary attention, and no specific investigations have been carried out after the excellent review performed by Adrain and Edgecombe (1996). The principal controversies about these faunas include their origin, their role in evolutionary events, and their paleobiogeographic significance (Elredge and Ormiston, 1979; Elredge and Branis¡a, 1980; Lieberman, 1993). Lower and Middle Devonian information about Maurotarion from Bolivia is of great significance, accounting for a monophyletic small-scale radiation hypothesis that involves five formally nominated species, separated in two informal groups (Adrain and Edgecombe, 1996). The origin of this clade has been explained by means of two independent migration events of cosmopolitan groups from low latitudes, one for Lochkovian-Pragian and the other during the Emsian, that were be interpreted to represent cladogenetic pulses, according to Adrain and Edgecombe (1996). Nevertheless, new evidences from eastern Bolivia confirm the presence of Maurotarion in South America already for the Silurian, questioning the nature and age of this evolutionary event (Edgecombe and Fortey, 2000). A sixth Emsian species from the Bokkeveld group of South Africa, of discussed affinities to the proposed informal groups, completes the list of known Malvinokaffric Maurotarion species up to the present (Cooper, 1982; Adrain and Edgecombe, 1996) In this scenario, the knowledge of Aulacopleurids from Argentina is very relevant. However, Malimanaspis sarudianskii (Baldis and Longobucco, 1977), Middle-Upper Devonian in age, from the Chigua Formation in western Precordillera is the only one Aulacopleurid described from this country. Unfortunately, this species is known from a single specimen poorly illustrated, and thus several diagnostic features are obscured. In this contribution the record of Lower Devonian Aulacopleurid trilobites from the Talacasto Formation in the Argentine Precordillera, is documented. A detailed taxonomic study based upon abundant and well preserved materials as well as related evolutionary implications is now in progress. Hence, systematic aspects and evolutionary significance of these new faunas are preliminary analyzed herein.