Study of the Histology of Leafy Axes and Male Cones of Glenrosa carentonensis sp. nov. (Cenomanian Flints of Charente-Maritime, France) Using Synchrotron Microtomography Linked with Palaeoecology

Jean-David Moreau,Éric Dépré,Paul Tafforeau,Didier Néraudeau

doi:10.1371/journal.pone.0134515

Jean-David Moreau, Éric Dépré + Show 2 more

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https://doi.org/10.1371/journal.pone.0134515

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Abstract

We report exceptionally well-preserved plant remains ascribed to the extinct conifer Glenrosa J. Watson et H.L. Fisher emend. V. Srinivasan inside silica-rich nodules from the Cenomanian of the Font-de-Benon quarry, Charente-Maritime, western France. Remains are preserved in three dimensions and mainly consist of fragmented leafy axes. Pollen cones of this conifer are for the first time reported and in some cases remain connected to leafy stems. Histology of Glenrosa has not previously been observed; here, most of internal tissues and cells are well-preserved and allow us to describe a new species, Glenrosa carentonensis sp. nov., using propagation phase-contrast X-ray synchrotron microtomography, a non-destructive technique. Leafy axes consist of characteristic helically arranged leaves bearing stomatal crypts. Glenrosa carentonensis sp. nov. differs from the other described species in developing a phyllotaxy 8/21, claw-shaped leaves, a thicker cuticle, a higher number of papillae and stomata per crypt. Pollen cones consist of peltate, helically arranged microsporophylls, each of them bearing 6–7 pollen sacs. The new high resolution tomographic approach tested here allows virtual palaeohistology on plants included inside a dense rock to be made. Most tissues of Glenrosa carentonensis sp. nov. are described. Lithological and palaeontological data combined with xerophytic features of Glenrosa carentonensis sp. nov. suggest that this conifer has been adapted to survive in harsh and instable environments such as coastal area exposed to hot, dry conditions.

Highlights

We describe a new species, Glenrosa carentonensis sp. nov
In the field of palaeobotany, until recently, synchrotron microtomography studies mainly dealt with small plant specimens removed from the sedimentary matrix [27,28,29,30,31,32,33,34,35,36,37,38,39,40]
Small blocks of rock embedded in a suitable resin and containing plant inclusions have been cut in order to obtain high resolution data [41]

Summary

Introduction

Have been previously reported from upper Albian and Cenomanian deposits of many localities of CharenteMaritime and Charente (Figs 1 and 2; [6, 8]). Preserved Glenrosa specimens have been recently recovered from this area inside Cenomanian flint nodules that preserve the cuticle and the histology of vegetative structures, as well as attached pollen-producing cones. The lowermost Cenomanian (A2) shows alternations of sand and clay beds, and yielded abundant and diverse plant meso-and macrofossils bearing cuticles [5, 6, 18]. Albian–Cenomanian deposits yielding plant fossils have been reported from several localities of western France such as Charente-Maritime [5], Dordogne [20], and Maine-et-Loire [21] (Figs 1 and 2). Glenrosa have been reported from the uppermost Albian (A1) of Cadeuil [22], Font-de-Benon (Archingeay- Les Nouillers; [15]) and Les Renardières (Tonnay-Charente; [12]); the lowermost Cenomanian (A2 and B1) of Font-de-Benon (Archingeay-Les Nouillers; [6]) and La Buzinie (Champniers); the upper lower Cenomanian (B2 and B3) of La Buzinie (Champniers; B.G. pers. obs.), Bois-Joli (Aix Island; [8]), Bois-Vert (Fouras; [5]); and the upper Cenomanian limestones (D) of Puits-des-Insurgés (Madame Island; D.N. pers obs.)

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