Intraspecific variation and polymorphism in the ostracode Conchoprimitian socialis (Brøgger, 1882) from the early Middle Ordovician Baltoscandian Palaeobasin

Abstract

The eridostracan ostracode genus Conchoprimitia Öpik, 1935 appears among the earliest ostracodes in the carbonate succession of the Ordovician Baltoscandian Palaeobasin. Over the past one hundred years, more than twenty species of Conchoprimitia have been recognized from early Middle Ordovician sediments. The microsculpture has been regarded as one of the most important features for distinguishing between different species of Conchoprimitia. However, four main types of microsculpture (smooth, punctate, reticulate and rugose/striate) are often transitional, occurring on different areas of the carapace and are not therefore discrete taxonomically important characters. As no clear distinction can be made between different carapace morphologies, the early Middle Ordovician Conchoprimitia species of Baltoscandia should be regarded as morphotypes of one polymorphic species -Conchoprimitia socialis (Brøgger, 1882). C. socialis was an opportunistic species, which developed different microsculpture on the carapace surface in different lithofacies in the Baltoscandian Palaeobasin.•

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

“…Öpik 1935;Henningsmoen 1953;Jaanusson 1957;Schallreuter 1993;Tinn et al 2010) and Avalonia (e.g. 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.…”

“…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.…”

“…Conchoprimitia is characterized by a very simple morphology and attains a relatively large size, sometimes exceeding 4 mm in length. Tinn et al (2010) mentioned recently in their comprehensive study on polymorphism in Conchoprimitia socialis (Brøgger, 1882) that this genus shows many intraspecific variations according to the habitats in which it occurs. The main variations observed include the size of the carapace, the presence or absence of a sulcus or muscles spots and the microsculpture.…”

“…Specimens of this species with retained valves are lacking in the studied material. Also, microsculpture is one of the important features for distinguishing a species of Conchoprimitia; despite this, our material includes casts of the external moulds only and it is almost impossible to determine the character of the carapace, if it is punctate/pitted, rugose/striate, or reticulate (see also Tinn et al 2010, fig. 7).…”

“…B). The genus Conchoprimitia is geographically widespread with a high abundance mainly in Baltoscandia (Tinn et al 2010). Some of its species are known from the Malopolska Block (Olempska 1994).…”