Abstract
Fossilized remains preserved in amber provide abundant data on the paleobiota surrounding the resin-producing plants, but relatively scarcer information about the resinous sources themselves. Here, dark pseudoinclusions in kidney-shaped amber pieces from the Early Cretaceous (Albian) amber from Spain are studied. This type of fossilized remain, abundant in Cretaceous ambers, was first interpreted as fossilized vacuole-bearing microorganisms, but later regarded as artifactual and probably secreted by the resinous trees, although their origin remained unclear. Using complementary microscopy (light, electron, confocal), spectroscopy (infrared, micro-Raman), mass spectrometry and elemental analysis techniques, we demonstrate that the pseudoinclusions correspond to droplets of phloem sap containing amber spheroids and preserving both organic and inorganic residues consistent with degraded components from the original sap. The amber pieces containing pseudoinclusions are fossilized, resin-in-sap-in-resin double emulsions, showing banding patterns with differential content of resin-in-sap emulsion droplets. Our findings represent the first time fossilized phloem sap, 105 million years old, has been recognized and characterized, and open new lines of paleontological research with taxonomic, taphonomic, physiological and ecological implications.
Highlights
Fossilized remains preserved in amber provide abundant data on the paleobiota surrounding the resinproducing plants, but relatively scarcer information about the resinous sources themselves
Microorganisms are known to have the potential for remarkable preservation in fossil resins, and a promising diversity of such organisms is known from Cretaceous amber (e.g.5,6), dark inclusions with a vacuolated appearance first described as fossilized vacuole-bearing microorganisms (e.g.7–11) were later regarded as non-microbial in origin, and termed pseudo-protists or pseudoinclusions[12,13,14,15,16]
We use morphological, taphonomic and chemical evidence obtained from microscopic, spectroscopic, mass and elemental analyses to prove that the amber pieces bearing abundant pseudoinclusions in the Rábago/El Soplao amber, which are common in other Cretaceous ambers, are composed of fossilized phloem sap and resin that originally mixed in double emulsion, as both immiscible liquids were extruded together
Summary
Fossilized remains preserved in amber provide abundant data on the paleobiota surrounding the resinproducing plants, but relatively scarcer information about the resinous sources themselves. Dark pseudoinclusions in kidney-shaped amber pieces from the Early Cretaceous (Albian) amber from Spain are studied This type of fossilized remain, abundant in Cretaceous ambers, was first interpreted as fossilized vacuole-bearing microorganisms, but later regarded as artifactual and probably secreted by the resinous trees, their origin remained unclear. The microbiological nature of these pseudoinclusions was first questioned on the basis of size range, spatial distribution, preferred orientation, and lack of surface ornamentation or inner structures, such as nuclei or organelles, based on material from mid-Cretaceous French amber[12,13,14] These pseudoinclusions were regarded as being either secreted by the resiniferous tree itself or as a product of the diagenetic polymerization of resin[13]. Kidney-shaped amber pieces are ideal to study pseudoinclusions, since their content in the latter is higher than that of other amber types and they are more suitable for destructive preparation due to their lack of valuable macroscopic bioinclusions
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