Microcodium is a problematic calcitic microfeature of many calcretes and calcareous paleosols in the Cretaceous and Tertiary continental and marine successions of the peri-Tethyan realm. The main controversy about the Microcodium structures is their origin and possible relation with calcified plant roots. Microcodium and rhizogenic (root-formed) microfabrics were studied in calcrete profiles within the Paleocene shallow-marine carbonate succession in southwestern Slovenia. The prominent laminar calcrete horizons contain abundant calcite aggregates, 150 m to 1 cm in size, with perfectly preserved structural details of plant root tissues. Morphology and structure of these aggregates indicate that they formed through biologically controlled precipitation of calcium carbonate within the root cortical cells. The morphologies intermediate between the typical Microcodium aggregates, composed of a single layer of individual, elongate pyramidal or prismatic crystals of calcite (measuring 100-500 m in length and 20-70 m in width) and calcified roots with multilayer arrangement of isodiametric cells were observed, and this supports previous rhizogenic interpretations of Microcodium structures. Intermediate forms show that the typical Microcodium aggregates formed through morphological transformation of the root tissue by growth of the calcite within the cortical cells, which distorted the cell shape. Calcification of roots and the creation of Microcodium structures can be explained as an effective nutrient-acquiring mechanism used by certain types of terrestrial plants inhabiting nutrient-poor calcareous substrates. The widespread occurrence of Microcodium in almost unaltered shallowmarine limestones indicates that its formation took place during early stages of paleosol development, probably reflecting specific types of vascular plants of a pioneer community that were able to colonize carbonate substrates during the early phases of subaerial exposure.

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International audiencePublished reports of amber predating the Aptian are rare and mention only amber pieces the size of millimetric marbles. Mid Cretaceous amber records, however, show a dramatic increase in number as well as in the size of the pieces, a phenomenon which is still poorly understood. The discovery of the first Jurassic deposit with comparatively large centimetric sized pieces of amber, in southern Thailand, is significant. Taphonomy and palaeobotany indicate a dense forest surrounding a coastal lake dominated by the resin-producing Agathoxylon tree. Since the palaeoecology of other amber-producing Jurassic and Cretaceous deposits is very similar a new hypothesis needs to be sought to explain the mid Cretaceous amber boom. It is suggested here that it was the result of a geological or taphonomic bias because coastal lacustrine environments are much better preserved after the Aptian on a worldwide scale

We report on very small fossil eggs from the Lower Cretaceous of Thailand, one of them containing a theropod embryo, which display a remarkable mosaic of characters. While the surficial ornamentation is typical of non-avian saurischian dinosaurs, the three-layered prismatic structure of the eggshell is currently known only in extant and fossil eggs associated with birds. These eggs, about the size of a goldfinch's, mirror at the reproductive level the retention of small body size that was paramount in the transition from non-avian theropods to birds. The egg-layer may have been a small feathered theropod similar to those recently found in China.

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