New Insights into the Early Diversification of the Ostracoda: Tremadocian Ostracods from the Cordillera Oriental, Argentina

Abstract

New species of ostracods from the Tremadocian in the northwest region of Argentina are described. These are among the earliest well−documented records of ostracods, which shed new light onto the early diversification of the group. The described fauna consists of seven species, five of which are new: Saltite uchuy sp. nov., Saltite kuraq sp. nov., Conchoprimitia? iglesiasi sp. nov., Orechina violetae sp. nov., and Orechina catalinae sp. nov. The fauna consists primarily of soanellids, a non−dimorphic family of palaeocopids, and of binodicopids. One factor leading to diversification of the group in this region may have been the complex configuration of the northwest basin, which had a restricted pattern of circulation. The distribution of the first ostracods is largely restricted to Gondwana and peri−Gondwana regions. Accordingly, it is possible to envision that the origin or at least an important radiation of the group was centred in this region. Both the Soanellidae and the genus Orechina would have originated in Gondwana and would have become widespread later during the Middle Ordovician. The Tremadocian fauna located in Argentina show significant affinities with fauna located in the warm−water setting of the east Gondwana, mainly in Australia and China.

Linguloidean brachiopods from the Lower Ordovician (Tremadocian) of northwestern Argentina

“…The lower part of the Humacha Member has been attributed to the sparsely fossiliferous unzoned interval between the Bienvillia tetragonalis and Notopeltis orthometopa biozones (Salas & Vaccari 2012), while its upper part could be assigned to the upper Tremadocian Notopeltis orthometopa Zone (Harrington & Leanza 1957, Waisfeld & Vaccari 2008a, Zeballo & Albanesi 2013.…”

The earliest ostracods from the Ordovician of the Prague Basin, Czech Republic

“…Siveter 2009), as discussed earlier by Dzik (1983) and Krůta (1988, 1994), and commented on more recent papers dealing with Early Ordovician ostracods of other regions, e.g. from Argentina (Salas et al 2007;Salas 2011;Salas and Vaccari 2012) and Iran (Ghobadi Pour et al 2011).…”

“…Some of its species are known from the Malopolska Block (Olempska 1994). It has also been recorded from other palaeocontinents: Avalonia (East Avalonia, Wales, Siveter 2009;West Avalonia, New Brunswick, Canada, Landing et al 2013) and from Gondwana (Ibero-Armorica, Vannier et al 1989;Cordilerra Oriental, Argentina, Salas 2011, Salas andVaccari 2012). However, due to homeomorphic species of this almost featureless genus (Tinn et al 2010;Williams et al 2003), their palaeobiogeographical interpretations may be confusing.…”

“…The earliest ostracod record, represented by the genus Nanopsis, comes from the mid Tremadocian of Baltica (Tinn and Meidla 2004). The ostracods were then already characterized by a wide geographical distribution as shown by their occurence in Gondwana (Cordillera Oriental, Argentina, Salas et al 2007, Salas andVaccari 2012;Alborz, Iran, Ghobadi Pour et al 2011), Avalonia (Williams and Siveter 1998) and Kazakhstan (Melnikova et al 2010). Based on data from Hou (1953), Ghobadi Pour et al (2011 suggested that some Tremadocian ostracods also occurred in China.…”

The earliest Ostracoda record from Brazil: Vila Maria Formation, Rio Ivaí Group, Paraná Basin, Central Brazil

“…iglesiasi Salas & Vaccari, 2012 from the Floresta Formation (Tremadocian) of the northwest Argentina, however the species differs in the very inconspicuous preadductorial node and adductorial sulcus and in the smooth lateral surface. C. frecuens Salas, 2011 from the middle to upper Floian of the Acoite Formation in northwest Argentina has a subcircular outline, a rounded adductorial muscle spot, an indistinct, V-shaped and short adductorial sulcus, a rugose lateral surface and a poorly defined bend between lateral and marginal surfaces.…”