Middle Jurassic Tethyan–Boreal ostracod faunal links: a case study from the Callovian of Portugal

Vanessa Pais,Liam Gallagher,Maria Cristina Cabral,Alan Lord,Ana Cristina Azerêdo

doi:10.1144/jmpaleo2015-035

Abstract

Late Callovian (athleta Chronozone) age sediments of Pedrogao, west coast Portugal, yielded a low diversity ostracod assemblage with relatively little in common with coeval NW European assemblages except at the weak level of comparative (cf.) species identification. Five new marine species are described ( Neurocythere multiforma sp. nov., Palaeocytheridea ( Malzevia )? dorsocostata sp. nov., Praebythoceratina parascrobiculata sp. nov., Praeschuleridea lisensis sp. nov., Virgulacytheridea posteroacuminata sp. nov.) and three previously described non-marine species recorded that so far are indigenous to Portugal ( Septacandona azeredae , Sinuocythere pedrogaensis , Theriosynoecum helmdachi ). Ostracod taxonomic links to western Tethys are evident but weak. Calcareous nannofossil assemblages were analysed for biostratigraphical control. Supplementary material: Sample data and raw ostracod counts are available at https://doi.org/10.6084/m9.figshare.c.3271394.v1

Highlights

According to Wilkinson & Whatley (2009), the morphological characteristics of the species stimulea can be variable, especially in the strength of ornamentation and of the median sulcus. Both the Toarcian and our Callovian material from Portugal and that figured by Wilkinson & Whatley (2009) differ from the material figured by Triebel & Bartenstein (1938) in the position, strength and orientation of the mid-ventral spine, which in the type material is a more prominent and ventrally-directed spine extending below the ventral margin
The taxonomic difficulties are well illustrated by Neurocythere multiforma sp. nov. which presented two problems: (1) similarity to but not precise identity with known species of the genus, and (2) the presence of a range of morphological variation that we interpret as three forms of a single species
Ostracod assemblages from the upper Callovian of western Portugal yielded (1) a marine association of 17 species: 5 species described as new (Praebythoceratina parascrobiculata, Praeschuleridea lisensis, Neurocythere multiforma, Virgulacytheridea posteroacuminata, Palaeocytheridea (M.)? dorsocostata), 1 previously described species (Gen. nov.? gublerae), 6 species compared with described taxa

Summary

Material and methods

Fifteen samples were collected from the marly beds of the Cabo Mondego ‘formation’ at Pedrógão, central-west coast of Portugal (Fig. 1); these samples were subsampled immediately after collection for calcareous nannofossil analysis. According to Wilkinson & Whatley (2009), the morphological characteristics of the species stimulea can be variable, especially in the strength of ornamentation and of the median sulcus Both the Toarcian and our Callovian material from Portugal and that figured by Wilkinson & Whatley (2009) differ from the material figured by Triebel & Bartenstein (1938) in the position, strength and orientation of the mid-ventral spine, which in the type material is a more prominent and ventrally-directed spine extending below the ventral margin. A species of Virgulacytheridea characterized by elongate carapace with a pointed, ventrally inclined posterior margin, with a subtle ornament of two fine ribs preserved in the postero-ventral area and a small ventrally-directed posterior spine.

Discussion

Conclusions

Acknowledgements and Funding