Papers by Philippe Steemans
Iawa Journal, 2019
Most evolutionary innovations in plant vascular tissues, including secondary growth, occurred dur... more Most evolutionary innovations in plant vascular tissues, including secondary growth, occurred during the Devonian period (~420 to 360 million years ago) and had a major impact on land colonisation by plants and on their biodiversity. The hydraulic conductance of the secondary xylem of three shrubby or arborescent mid-late Givetian or earliest Frasnian plants (a probable new genus of Cladoxylopsida, the archaeopteridalean genus Callixylon and the stenokolean genus Brabantophyton) is examined for the first time. Plant fossils come from the Ronquières fossil site of Belgium. Results show that hydraulic conductivity of these early woody plants is more or less similar to that of modern gymnosperms, meaning water transport was already as efficient in Devonian plants as it is in living plants. Our results further suggest that tracheids with features helping for optimized water transport were quickly selected in the evolutionary history of vascular plants.
Recently discovered outcrops of post-glacial Early Palaeozoic mudstones in northern Ethiopia have... more Recently discovered outcrops of post-glacial Early Palaeozoic mudstones in northern Ethiopia have yielded a well-preserved assemblage of cryptospores (e.g., Rugosphaera rugosa, Segestrespora laevigata, Tetrahedraletes medinensis, Velatitetras laevigata and V. retimembrana). These palynomorphs represent the first biostratigraphic evidence of Early Palaeozoic sediments in NE Africa and have the potential to shed light on the postHirnantian plant colonization of Gondwana.
First clear data of land-living plants in form of cryptospores in Gondwanan sediments dates well ... more First clear data of land-living plants in form of cryptospores in Gondwanan sediments dates well back into the Middle Ordovician. However, the earliest macroplant remains do not appear before the Mid Silurian. In the time between, plant evolution on terrestrial environments in Gondwana was severely hampered by the Hirnantian glaciation event. The nature of the plants remains mysterious. How did they survive the glaciation and how did they recolonise once glaciated areas? First answers to these questions are expected from fine-grained early postglacial continental or marginal marine sediments because of their promising potential for macroflora preservation. However, such deposits are rare in Gondwana with the fossil record highly biased towards marine sediments.
Palaeontologia Electronica, 2017
In Australia, lycopsids are abundant in early land plant assemblages, leading to the concepts of ... more In Australia, lycopsids are abundant in early land plant assemblages, leading to the concepts of a "Baragwanathia flora" extending from the late Silurian to the Early Devonian, and a "Leptophloeum flora" characterizing the Late Devonian. Yet, the taxonomic status and systematic affinities of a large number of lycopsid remains from the Devonian of Australia are poorly resolved. The contribution of such lycopsids to the diversification of the group and the evolution of the rhizomorphic lycopsids is unknown. In this paper we investigate the three-dimensional organization of a new structurally preserved cone using X-ray synchrotron microtomography. This large and compact bisporangiate cone, which was collected at Barraba, a Famennian locality in northern New South Wales, represents a new genus, Cymastrobus. Its sporophylls are comprised of a poorly preserved lamina and a long narrow pedicel enlarging distally and possessing an abaxial keel and a heel. Megasporangia contain a large number of megaspores. Their central body show several rows of small circular structures surrounding the trilete mark. Microspore remains are of the Endosporites-type. Cymastrobus is close to the contemporaneous genus Bisporangiostrobus and to the Carboniferous taxon Flemingites. It may have occupied a basal position in the phylogeny of the rhizomorphic lycopsids.
Review of Palaeobotany and Palynology, 2021
Gondwanan floras of Late Devonian age are poorly known. In Australia, the rare studies that have ... more Gondwanan floras of Late Devonian age are poorly known. In Australia, the rare studies that have been published on Late Devonian plants are old and need reinvestigation. This paper is an account of the plant macro-and micro-remains found in the Mandowa Mudstone at Barraba, New South Wales. According to the miospores, plants are late to latest Famennian in age. The record of anatomically preserved specimens is diversified, with nine taxa assigned to the Lycopsida, Cladoxylopsida, Iridopteridales and Archaeopteridales. One specimen is referrable to the spermatophytes. Several taxa are specific to Barraba, i.e., the lycopsid genera Cymastrobus and Lycaugea, the iridopteridalean genus Keraphyton, the cladoxylopsid species Polyxylon australe, and possibly a plant represented by a large Hierogramma branch showing exarch protoxylem strands. The adpression record is dominated by axes of the cosmopolitan lycopsid genus Leptophloeum. It also includes specimens interpreted as seed plants such as a possible ovule resembling Pseudosporogonites, and two types of foliage differing by their petiole width. One of this foliage consists of delicate fronds broadly comparable to those of Cosmosperma. The closest flora from Barraba is the late Famennian-earliest Click here to view linked References Tournaisian flora of the New Albany Shale in eastern USA, suggesting floral connexion and comparable environmental conditions between Northern Gondwana and Southern Laurussia.
Lethaia, 2019
Land plants comprise the bryophytes and the polysporangiophytes. All extant polysporangiophytes a... more Land plants comprise the bryophytes and the polysporangiophytes. All extant polysporangiophytes are vascular plants (tracheophytes), but to date, some basalmost polysporangiophytes (also called protracheophytes) are considered non-vascular. Protracheophytes include the Horneophytopsida and Aglaophyton/Teruelia. They are most generally considered phylogenetically intermediate between bryophytes and vascular plants and are therefore essential to elucidate the origins of current vascular floras. Here, we propose an alternative evolutionary framework for the earliest tracheophytes. The supporting evidence comes from the study of the Rhynie chert historical slides from the Natural History Museum of Lille (France). From this, we emphasize that Horneophyton has a particular type of tracheid characterized by narrow, irregular, annular and/or, possibly spiral wall thickenings of putative secondary origin, and hence that it cannot be considered non-vascular anymore. Accordingly, our phylogenetic analysis resolves Horneophyton and allies (i.e. Horneophytopsida) within tracheophytes, but as sister to eutracheophytes (i.e. extant vascular plants). Together, horneophytes and eutracheophytes form a new clade called herein supereutracheophytes. The thin, irregular, annular to helical thickenings of Horneophyton clearly point to a sequential acquisition of the characters of water-conducting cells. Because of their simple conducting cells and morphology, the horneophytophytes may be seen as the precursors of all extant vascular plant biodiversity. □ Cladistics, Horneophyton, lower Devonian, Rhynie chert, tracheophyte. Borja Cascales-Miñana ✉ [
Palaeogeography, Palaeoclimatology, Palaeoecology, 2015
The oldest seed occurrences in Western Gondwana have been recognized in a new stratigraphic secti... more The oldest seed occurrences in Western Gondwana have been recognized in a new stratigraphic section located in Western Argentina (Precordillera Basin). Palynological evidence indicates an Early Mississippian (probably Tournaisian) age for this new succession. The two identified early seeds generas, Pseudosporogonites cf. hallei and Warsteinia sancheziae n. sp. were up to now considered as restricted to the Devonian of Laurussia. This finding suggests a dispersal of earliest spermatophytes between Laurussia and Gondwana during Devonian/ Tournaisian times, thus accounting for the Rheic Ocean as a surmountable biogeographic barrier for continental biotas. Alternatively, contrasting biogeographic hypotheses dealing with early spermatophytes rising in paleotropics and then displacing herbaceous communities of non-spermatophytes typical from cool high latitudinal regions, are explored for explaining the recognized paleobiogeographical pattern. The new information supports a weak impact of the Devonian/Carboniferous biotic crisis on earliest seed plant diversity. Based on preliminary evidences of niches differentiation and ecological dynamics probably affected by wildfires, Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought, and more similar to those reported from Laurussia. In addition, their discovery in a sedimentary environment associated to glacigenic deposits, show that this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana.
Science, 2011
The earliest evolution of wood occurred in plants of surprisingly small stature.
Geological Magazine, 2013
This study is concentrated on Ludlow (to Pridoli?) miospores from the Los Espejos Formation at th... more This study is concentrated on Ludlow (to Pridoli?) miospores from the Los Espejos Formation at the Quebrada Ancha locality, Central Precordillera, San Juan Province, Argentina. The Ludlow age is in agreement with the age based on acritarchs. The assemblage of continental palynomorphs is composed of 43 miospore species (29 trilete spores and 14 cryptospores). A new synonymy is proposed: Chelinospora poecilomorpha is here considered a junior synonym of Clivosispora verrucata. In addition, specimens belonging to C. verrucata var. verrucata and C. verrucata var. convoluta are included in a new morphon. This study represents the second Late Silurian miospore assemblage described from South America; the first was from the Urubu River, Amazon Basin, northern Brazil. The Quebrada Ancha assemblages allow a reasonably good correlation with biozones established for the Upper Silurian from the Cantabrian Mountains, northern Spain. The dendrogram analysis between coeval miospore assemblages from...
Well-preserved palynomorph assemblages are recovered from the Devonian Jauf and Jubah formations ... more Well-preserved palynomorph assemblages are recovered from the Devonian Jauf and Jubah formations in five shallow boreholes in the northern part of Saudi Arabia. These fully cored boreholes overlap stratigraphically to form a 1640 ft composite sequence. Miospores dominate the palynological assemblages of most samples. The assemblages are mainly composed of trilete spores but also contain cryptospores and monolete spores. One new genus, sixteen new species and two new varieties of miospores are described from the studied assemblages:
Current palaeobotanical research on the Scladina cave (Meuse basin, Belgium). 16h00-16h20: L. Vry... more Current palaeobotanical research on the Scladina cave (Meuse basin, Belgium). 16h00-16h20: L. Vrydaghs -Entre prairies et labours : l'analyse phytolitairenne des lames minces des terres noires bruxelloises (10 è -13 è siècles AD). 16h20-16h50 : E. Roche -Palynologie du Quaternaire: distinguer les effets climatiques des effets anthropiques, mythe ou réalité ? Deux exemples: la Tunisie septentrionale et l'Afrique centrale.
Earth and Environmental Science Transactions of The Royal Society of Edinburgh, Dec 1, 2017
Running head: Spores from the Lower Devonian Posongchong Formation * Retusotriletes rotundus (Str... more Running head: Spores from the Lower Devonian Posongchong Formation * Retusotriletes rotundus (Streel) Streel 1967 in original source. Appendix. Known Posongchong spore diversity (continued)
Review of Palaeobotany and Palynology
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Geologica Belgica, 2021
Accurate palyno-analysis by S. Loboziak (from 1980 to 1983) of 28 samples from the Upper Givetian... more Accurate palyno-analysis by S. Loboziak (from 1980 to 1983) of 28 samples from the Upper Givetian to the Middle Frasnian Blacourt, Beaulieu and Ferques Formations and of 44 samples of the Upper Frasnian to the Lower Famennian Hydrequent Formation are re-evaluated. Chelinospora concinna, Verrucosisporites bulliferus, Cirratriradites jekhowskyi, Lophozonotriletes media first occurrences are major criteria for Lower and Middle Frasnian, well calibrated by conodonts. Cymbosporites acanthaceus, Rugospora bricei, Grandispora gracilis, Diducites plicabilis, Corbulispora vimineus first occurrences allow to subdivide the Upper Frasnian where conodonts are poorly present. Samarisporites triangulatus versus Auroraspora pseudocrista taxonomy and stratigraphic significance are discussed. The reconnaissance borehole Nieuwkerke-De Seule (95W152), near the limit of the Upper Palaeozoic subcrop on the Brabant Massif (West Flanders, Belgium, 75 km east of the Boulonnais), which has intersected conodo...
9th EPPC Padova 2014 Arabian Plate sequence stratigraphy of the Cambrian to early Silurian interv... more 9th EPPC Padova 2014 Arabian Plate sequence stratigraphy of the Cambrian to early Silurian interval After Sharland et al. (2001) and correlation with coeval succession of North Africa Phanerozoic cycles of sea-level change on the Arabian Platform
is a sedimentary sequence in DRC unaffected by regional metamorphism . It consists of two distinc... more is a sedimentary sequence in DRC unaffected by regional metamorphism . It consists of two distinct successions: a lower, ~500 m thick siliciclastic sequence of the BI Group (dated at 1125 Ma or between ca. 1175 Ma and 882 Ma (Delpomdor et al. (2013)) and an upper, ~1000 m thick carbonate sequence with stromatolitic build-ups and black shales of the BII Group directly overlain by basaltic lavas dated at 948 ± 20 Ma (Cahen et al., 1984). Five boreholes from Sankuru -Mbuji-Mayi region have been sampled in detail. A well preserved and diversified microfossil assemblage is reported including 54 taxa belonging to 32 genera. The typical late Mesoproterozoic -early Neoproterozoic acritarch, Trachyhystricosphaera aimika, is reported herein for the first time in central Africa, and co-occurs with other eukaryotes and prokaryotes. The available biostratigraphic data enable to suggest a minimum Tonian, pre-Sturtian age for the Mbuji-Mayi Supergroup. This age is consistent with the published and new geochronological data . Comparison with worldwide Proterozoic assemblages permits to define microfossil assemblages useful for biostratigraphy (Baludikay et al., submitted). Moreover, δ 13 Ccarb positive and negative excursions in the BIe -BIIc interval are similar to variations in late Mesoproterozoic -early Neoproterozoic carbonate successions , Halverson et al. 2010
Acta Palaeontologica Polonica, 2018
Review of Palaeobotany and Palynology, 2021
An integrated palynological and geochemical approach has been initiated to date and to precise th... more An integrated palynological and geochemical approach has been initiated to date and to precise the geochemical events of the Pimenteiras Formation, in the Late Devonian from the Parnaíba Basin, Brazil. Based on good biostratigraphic markers and presence of index species among miospores, acritarchs and chitinozoa, the investigated sequences are referred to the Middle to early Late Frasnian. Among Miospores, Chelinospora concinna and Verrucosisporites bulliferus are likely to be from the BPi Interval Zone defined in the Amazon Basin. Chitinozoans of the Early to early Late Frasnian Angochitina (Lagenochitina) avelinoi zone of the Parnaíba Basin are present, and acritarch assemblages are also consistent with a Middle to early Late Frasnian age, by comparison to assemblages previously described in other Brazilian basins. Some important accompanying species of palynomorphs are illustrated. In the studied outcrops, black shale intervals are referred to top of the Radioactive Sale B and Radioactive Shale C according to Rodrigues (1995) definitions. Top of Radioactive Shale B shows good concentration of terrestrial organic matter, but low potential source of gas. By comparison Radioactive Shale C of the upper part of the Pimenteiras Formation, with important concentration of marine organic matter have low to high potential as source of gas and condensate. This study shows that a progressive flooding took place during the Devonian period in the Parnaíba Basin with maximum marine transgression in the Frasnian. These global events of interest for hydrocarbon exploration, are regarded as markers for Gondwanan regional chronostratigraphic correlations.
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Papers by Philippe Steemans