Search

Tyloses are swellings of parenchyma cells into adjacent water-conducting cells that develop in vascular plants as part of heartwood formation or specifically in response to embolism and pathogen infection. Here we document tyloses in Late Devonian (approximately 360 Myr ago) Callixylonwood. This discovery suggests that some of the earliest woody trees were already capable of protecting their vascular system by occluding individual conducting cells.

ABSTRACTFrench Lower Devonian floras are rare, especially compared to certain other Western European countries. In this study, we reassess an assemblage collected in the 1930s in the Rebreuve quarry (Pas-de-Calais, northern France). We describe new features in several taxa and update taxonomic names from original descriptions. For instance, re-examination of vegetative remains previously described as Psilophyton princeps, led to the discovery of fertile structures allowing us to refer these specimens to Sawdonia. In total, this flora consists of 10 taxa, including up to four different Psilophytonspecies, such as P. parvulum. Other taxa include Danziella artesiana, Drepanophycuscf. spinaeformis, Sporogonites exuberansand some specimens of Taeniocradaand Sciadophyton, revealing a diverse Lower Devonian plant assemblage. The Rebreuve assemblage represents a typical Emsian flora from Laurussia and bears striking resemblance with coeval Belgian assemblages. Previous palynological investigations, in addition to the similarities with well-dated Belgian floras, suggest an early Emsian age for this assemblage. The paleogeographical implications of findings are discussed.

ABSTRACTThe Mississippian is characterized worldwide by a general cooling of the environment and a climatic stratification of Earth. Argentina at that time was part of the megacontinent Gondwana. It occupied a position close to the South Pole around 60°S. Whereas paleoequatorial and paleotropical floras are relatively well known, higher latitude environments are still poorly understood. In this framework, a revision of Mississippian deposits is ongoing in Argentina. An extensive and detailed survey of the Sierra de las Minitas (La Rioja Province, western Argentina) involved drawing detailed sections and the systematic verification of all rock layers. Fossils were sampled and studied in the laboratory. We describe a new isoetalean lycopsid with a rare combination of characters. This plant presents an estimated low stature (approximately 30 cm), a branched rhizomorph, an inflated intermediary zone, a monocaulous growth form and evidence for cyclic fertility. These features are interpreted as representing specific adaptations to the harsher tundra conditions prevailing in the Lower Carboniferous Southern Polar environments.

The Late Paleozoic Ice Age (LPIA) has been well recorded in the uppermost Mississippian–Pennsylvanian of Gondwana. Nevertheless, little is known about the temporal and geographic dynamics, particularly during the early Mississippian. We report on exceptional Tournaisian glaciomarine stratigraphic sections from central Argentina (Río Blanco Basin). Encompassing c. 1400 m, these successions contain conspicuous glacigenic strata with age constraints provided by palaeontological data and U/Pb detrital zircon age spectra. A variety of marine, glaciomarine and fan-deltaic environments indicate relative sea-level variations mainly associated with tectonism and repetitive cycles of glacial activity. Provenance analysis indicates a source from the Sierras Pampeanas basement located to the east. Fifteen sequences were grouped into three depositional models: (1) Transgressive Systems Tracts (TST) to Highstand Systems Tracts (HST) sequences unaffected by glacial ice; (2) Lowstand Systems Tracts (LST) to TST and then to HST with glacial influence; and (3) non-glacial Falling-Stage Systems Tracts (FSST) to TST and HST. The glacial evidence indicates that the oldest Mississippian glacial stage of the LPIA in southwestern Gondwana is constrained to the middle Tournaisian. In contrast with previous descriptions of Gondwanan coeval glacial records, our sequence analysis confirms complex hierarchical climate variability, rather than a single episode of ice advance and retreat. Supplementary material: Detailed stratigraphic sections, palaeocurrents and compositional analysis and U/Pb detrital Zr methodology and data are available at: https://doi.org/10.6084/m9.figshare.c.5011424 [ABSTRACT FROM AUTHOR]

ABSTRACTThis paper discusses the main steps leading to the acquisition, during the Palaeozoic, of the seed habit. The earliest spermatophytes originated in the Late Devonian and produced small cupulate ovules characterized by an elaborated sporangial apex involved in pollination. The diversification of ovules during the Carboniferous led to a wider range of sizes and shapes, and an increasing importance of the integument. The earliest seeds containing embryos are reported in Carboniferous coniferophytes.