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First record of discinid brachiopods from Late Jurassic Plattenkalk deposits

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First record of discinid brachiopods from Late Jurassic Plattenkalk deposits of southern Germany
2017 Poster REICH&Al discinid brachiopod
Adobe Acrobat Dokument 40.9 MB

Autoren: Mike Reich, Alexander M. Heyng, Bork Ilsemann, Alexander Nützel & Tanja R. Stegemann

Präsentation: 88. Jahrestagung der Paläontologischen Gesellschaft, 26.-30. März 2017, Münster

 

Introduction

The Kimmeridgian and Tithonian Plattenkalk deposits of southern Germany (e.g., Solnhofen, Eichstätt, Pfalzpaint, Painten, Brunn, Wattendorf) are famous for their diverse and exceptionally preserved fauna and flora. So far, there are around 1,800 species, mostly macrofossils, reported from these strata. However, with the help of non-applied or hitherto unused micropalaeontological methods, new (or so far unrecorded) species or groups can be detected.

 

In the present study we report the first find of organophosphatic-shelled brachiopods (Linguliformea: Discinoidea) from the Late Jurassic Plattenkalk deposits of southern Germany.

 

Fossil and modern Discinida

Linguliform brachiopods were major components of marine assemblages from the Early Cambrian onwards, but their evolution and palaeogeography during the Jurassic–Cretaceous is poorly understood, as a result of a sparse fossil record.

Discinid brachiopods are epifaunal, fixo-sessile invertebrates, common in some Recent environments (intertidal) and attached by a highly muscular pedicle to various hard substrates. The discinid pedicle acts as an anchor, and it supports the weight of the shell and holds it in relative position to the substrate. The ventral valve is always oriented toward the substratum (Fig. A), a feature that discinids share with craniids and articulate thecideid brachiopods. Modern discinids (solitary or known in clusters; Fig. B) have a cryptic mode of life on the underside of pebbles or attached to larger boulders embedded in soft substrate.

In the fossil record (since the Ordovician), discinids are also known attached to articulate brachiopods, bivalves, cephalopods, and conulariids.

 

Importance of the material

As already stated this is the first record of organophosphaticshelled brachiopods from Late Jurassic Plattenkalk deposits of southern Germany. Summarized, our data reveal a linguliform brachiopod diversity hitherto unknown from Jurassic Plattenkalk Lagerstätten. The new recorded data will help to develop a more detailed palaeobiodiversity as well as palaeoecological interpretation of Late Jurassic Plattenkalk deposits in southern Germany. The discovery of a diverse discinid brachiopod fauna offers in part new insight into palaeoenvironmental patterns and former benthic habitats of the Late Jurassic Solnhofen Archipelago. The applied micropalaeontological methods in isolating microscopic/mesoscopic invertebrates is seen to be promising for the study of neglected or overlooked fossils in general.

 

Results

Discinid brachiopod shells (especially ventral valves) are generally rare in the Mesozoic/Cenozoic fossil record, therefore they have often been taken to indicate a low preservational potential. The here presented organophosphatic brachiopod material is based on >100 (microscopic / mesoscopic) isolated valves (rock disintegration by using buffered acetic acid) from the Early Tithonian Mörnsheim Formation (Hybonotum Zone: Moernsheimensis Subzone, ~149 Ma; Fig. C) of two sections in Mühlheim near Solnhofen, Upper Bavaria, Germany.

 

Three species of the Discinidae (Figs. D-G) can be identified from our strata, including a new genus and species (related to Discinisca and Discradisca). In addition, we documented the associated macro-, meso-, and microfauna (Reich et al. in prep.) of the studied sections. All recorded discinid brachiopods are associated with sponges (Hexactinellida, Demospongea), bivalves and other invertebrates and microfossils. 

 

Acknowledgements: We are indebted to Marlena Olbrys (formerly LMU Munich) for technical help. Furthermore, we would like to thank the owners and operators of the Mühlheim quarries, Ulrich Leonhardt, Roland Pöschl, and Uwe Krautworst, for logistics and support.

 

Published online 19-12-2017 by M. Reich, A. M. Heyng, B. Ilsemann, A. Nützel & T. R. Stegemann