100-million-year-old conifer tissues from the mid-Cretaceous amber of Charente (western France) revealed by synchrotron microtomography

Abstract

Background and Aims Terrestrial plant remains in fossilized tree resin are relatively common. However, histology and preservation of plants entombed in Cretaceous ambers remain poorly known. We report an exquisitely preserved conifer leafy axis from 100-million-year-old opaque amber of western France that is assignable to Glenrosa carentonensis Moreau, Néraudeau, Tafforeau & Dépré. The purpose of this paper is to discuss the taphonomy and the use of microtomography for studies of palaeobotanical remains in amber.Methods A leafy axis was examined using propagation phase-contrast X-ray synchrotron microtomography with voxel sizes of 14Á9, 1Á4, and 0Á7 lm.Key Results The conifer leafy axis described is preserved in three dimensions. Despite desiccation of the specimen within the surrounding amber, the cuticle, as well as most of inner tissues, is preserved in three dimensions down to the cellular level. Epidermis, palisade parenchyma, spongy parenchyma, transfusion tracheids and vascular bundles are clearly distinguished.Conclusions Gross morphology and histology of the specimen were revealed using synchrotron microtomography, allowing an unprecedented resolution for the study of soft-bodied plants entombed in amber. The study reveals a peculiar combination of authigenic and duripartic preservation as well as permineralization, and highlights the complexity of taphonomic processes that can occur in amber inclusions. This fossil demonstrates the difficulty of studying amber-preserved plant remains under certain conditions.

Plant Tissue Decay in Long-Term Experiments with Microbial Mats

“…For instance, a dorsoventral gradient in the decay through leaf sections occurred in the mummified fossils of the taxodiaceous conifer Metasequoia Hu and Cheng found at the Buchanan Lake Formation (Eocene, Canada) [88]. This gradient of preservation was also observed in other plant fossils, such as the exceptionally well-preserved specimens from Charente-Maritime (Cenomanian, western France); while several tissues, such as the stomatal crypts, were undamaged, and fossilized, spongy parenchyma was only partially conserved [84,89]. In addition, based on these results, the present model of preservation in mats unifies the two categories for the exceptional preservation of plant fossils [41].…”

Conifers from the Cenomanian amber of Fouras (Charente-Maritime, western France)

“…Plant remains such as bryophytes, conifer leafy axes, ferns, and flowers have been reported in Cretaceous amber from many localities worldwide (Chambers et al, 2010;Crepet et al, 2016;Ignatov et al, 2016;Schneider et al, 2016;Moreau et al, 2017a;Kvaček et al, 2018). However, such fossil inclusions remain extremely rare in the French Cretaceous amber which has otherwise yielded abundant and diverse fossils of arthropods (Néraudeau et al, 2002(Néraudeau et al, , 2008Nel et al, 2004;Perrichot, 2005Perrichot, , 2015Perrichot et al, 2008aPerrichot et al, , 2008bPerrichot et al, , 2010, microorganisms (Breton and Tostain, 2005;Girard et al, 2009), as well as rare vertebrate integuments (Perrichot et al, 2008c;Vullo et al, 2010a).…”

“…Plant meso-or macroremains found in this amber are commonly indeterminable, altered, and limited to stellate hairs (Girard, 2010), or tiny fragments of cuticle or wood sometimes preserved as partially empty casts (Perrichot, 2005;Girard et al, 2013). Until now, a single foliar plant remain was described in amber from La Buzinie in the Charente department (Moreau et al, 2017a). It consists of an exquisitely preserved conifer leafy axis ascribed to Glenrosa carentonensis Moreau, Néraudeau, Tafforeau & Dépré, an extinct Cretaceous taxon characterized by an unusual stomatal arrangement inside crypts (Moreau et al, 2015).…”

Araucarian conifer from late Albian amber of northern Spain

“…; Moreau et al . ). Plant remains preserved in amber provide an opportunity to study plants in particular detail.…”