Thomas Servais

• Dr sc, HDR
• Directeur de Recherches CNRS at French National Centre for Scientific Research

The Early Devonian plant fossil record provides evidence of large vegetation turnover events in addition to rapid morphological and anatomical changes among vascular plants. The Ardenno-Rhenish Massif has historically yielded a vast number of these plant fossils allowing us to obtain a nearly unparalleled snapshot of Early Devonian vegetation. None...

Acritarchs have largely been used for biostratigraphical purposes, mostly in the early Palaeozoic, when they were the most abundant and diversified group of organic-walled microfossils. Our literature review shows that more than 4000 species have been described throughout the Palaeozoic. Taxonomical reviews of several acritarch genera, including bi...

Global cooling has been proposed as a driver of the Great Ordovician Biodiversification Event, the largest radiation of Phanerozoic marine animal Life. Yet, mechanistic understanding of the underlying pathways is lacking and other possible causes are debated. Here we couple a global climate model with a macroecological model to reconstruct global b...

Acritarchs are an informal, polyphyletic, and morphologically heterogenous group of organic-walled microfossils of unknown biological affinity. Some acritarchs share morphological similarities with certain microplankton resting stages (from e.g., dinoflagellates, prasinophycean-, chlorophycean-, and zygnematophycean green algae), others with miospo...

A poorly diverse trilobite assemblage is described from the Tremadocian strata (Tangissart Member of the Mousty Formation; Chevlipont Formation) of the Brabant Massif. These specimens represent so far the oldest trilobite record from Belgium. The recorded taxa, identified as Platypeltoides cf. croftii, Macropyge? sp., and Asaphidae indet., resemble...

The Silurian-Devonian plant radiation was a critical development in the evolution of early terrestrial ecosystems. Characterizing the diversity dynamics of this radiation has been a focus of numerous studies. However, little is known about the impact of geological bias on our perception of this biodiversification. Here, we use a new, comprehensive...

The Ordovician was a key period in the history of the Earth. “A Global Synthesis of the Ordovician System” is presented in two volumes of the Geological Society Special Publications series. The first volume (SP 532) covers general aspects of the Ordovician and includes the syntheses of the Ordovician successions of Europe. To provide a comprehensiv...

The Ordovician was a key period in the biological and geological history of the planet. ‘A Global Synthesis of the Ordovician System’ is presented in two volumes of The Geological Society, Special Publications . This first volume (SP532) charts the history of the Ordovician System and explores significant advances in our understanding of the period...

The Silurian–Devonian plant radiation was an event triggered by the progressive colonization of subaerial habitats. Nevertheless, it is still unclear whether this radiation was globally uniform or whether alternative diversification scenarios emerged depending on the geographical context. Here, we report on early land plant diversity patterns acros...

The Ordovician successions of France and neighbouring areas of Belgium and Germany are reviewed and correlated based on international chronostratigraphic and regional biostratigraphic charts. The same three megasequences related to the rift, drift, and docking of Avalonia with Baltica can be tracked in Belgium and neighbouring areas (Brabant Massif...

New palynological studies from the Xiaoyangqiao section (Jilin Province, NE China), which has been selected as an Auxiliary Boundary Stratigraphic Section and Point (ASSP) for the base of the Ordovician Series, confirm the presence of Goniomorpha Yin 1986 in intervals ranging from the late Cambrian (Furongian) to the Early Ordovician (Tremadocian),...

The Ordovician System was introduced by Charles Lapworth as solution to the overlapping unit stratotypes loosely defined by Adam Sedgwick, for the Cambrian, and Roderick Murchison, for the Silurian. The Ordovician has emerged as one of the longest and most significant of the geological periods. Following an interval of intensive research of all the...

Due to increasing availability of data for many fossil groups and a generally accepted palaeogeographical configuration, palaeontologists have been able to develop progressively more robust palaeobiogeographical scenarios for the spatial distributions of Ordovician marine faunas. However, most research in Early Palaeozoic palaeobiogeography centers...

The Lower Devonian Klerf Formation is an exceptional Konservat-Lagerstätte, exposed at multiple sites in the Waxweiler region in the Eifel area, western Germany. It has been studied for its various fossils, mainly arthropods, fishes, plants, molluscs, brachiopods, and crinoids. At Waxweiler, the sediments are palaeoecologically interpreted as a pro...

Global cooling during the Ordovician (485 Ma to 443 Ma) has long been considered as a possible driver of the Great Ordovician Biodiversification Event (GOBE), the largest radiation of Phanerozoic marine animal Life. Yet, this hypothesis exclusively relies on temporal correlations. Mechanistic understanding of the underlying pathways is lacking and...

This contribution reviews the evidence for terrestrial organisms during the Ordovician (microbial, land plant, fungal, animal) and for the nature of the terrestrial biota. The evidence regarding the origin and early diversification of land plants combines information from both fossils and living organisms. Extant plants can be utilised in: (i) phyl...

The Ordovician is one of the longest and geologically most active periods in Phanerozoic history. The unique Ordovician biodiversifications established modern marine ecosystems, whereas the first plants originated on land. The two volumes cover all key topics on Ordovician research and provide a review of Ordovician successions across the globe.

The Ordovician is one of the longest and geologically most active periods in Phanerozoic history. The unique Ordovician biodiversifications established modern marine ecosystems, whereas the first plants originated on land. The two volumes cover all key topics on Ordovician research and provide a review of Ordovician successions across the globe.

In our recent publication on the biodiversity of Paleozoic phytoplankton (Kroeck et al., 2022) we cited several works of Martin (Martin, 1996; Martin and Quigg, 2012; Martin and Servais, 2020) to present the hypothesis that during the late Paleozoic nutrient availability in the oceans increased significantly from a rather (super-) oligotrophic earl...

The oldest reported occurrence of cryptospores supposed to derive from land plants (embryophytes) is currently considered to be in the Middle Ordovician. The two genera Virgatasporites and Attritasporites, described in the 1960ʹs from the Early Ordovician (Tremadocian) of Algeria, are morphologically close to the miospores, and therefore pose a dil...

Phytoplankton form the base of most marine trophic chains and studying their past diversity at regional and global scales can provide valuable insights into the evolution of marine ecosystems and climate history. Using a new database of more than 4000 species of acritarchs and prasinophytes, a comprehensive investigation of the taxonomic diversity...

During the mid-Palaeozoic, vascular land plants (i.e., tracheophytes) underwent a great radiation that triggered the development of the land biosphere – the so-called Silurian–Devonian terrestrial revolution. However, little is known about how different plant groups impacted this process. A newly constructed dataset of plant macrofossil genera is u...

Palaeozoic acritarchs mostly represent organic-walled cysts of marine phytoplankton, and therefore, as primary producers, played an important role in the evolution of marine ecosystems. In this study, we use a selection of the most abundant acritarch taxa from the Cambrian and Ordovician of China to understand the evolution of the palaeoecological...

Diversification is a key property of life. Building on John Phillips' (1860) classic, iconic curve, Phanerozoic biodiversity trajectories have been based, subsequently, on the availability of additional and renewed sets of data and increasingly sophisticated analytical methods. Using relatively few single sources of data from global databases, the...

The Ordovician biodiversification is considered one of the most significant radiations in the marine ecosystems of the entire Phanerozoic. Originally recognized as the Ordovician Radiation, a label retained during most of the 1980s and 1990s, the term Great Ordovician Biodiversification Event (GOBE) was coined in the late 1990s and was subsequently...

The Rhynie chert (Aberdeenshire, Scotland, UK) plant Horneophyton lignieri is likely one of the most studied elements of Lower Devonian floras considering both macro and microremains. Intriguingly, while larger plant fragments are exceptionally fossilized, in situ spores are not necessarily well-preserved in the chert: they are dark brown and inten...

Palynological investigations have been carried out on samples from the Upper Devonian Hongguleleng Formation of Western Junggar, Xinjiang, NW China. In total, 26 miospore species belonging to 19 genera and 28 acritarch species assigned to 19 genera have been recognized from the lower member of the Hongguleleng Fm. in the Bulongguoer section. The pa...

Lower Ordovician brachiopod macrofaunas in Belgium (Avalonia) are seldom collected and studied due to the poor preservation of material. Here we describe a new fauna of linguliformean brachiopods from the Chevlipont Formation (lower Tremadocian) in the Brabant Massif. The fauna is of low diversity (at least three species belonging to Rosobolus?, Th...

Investigation of large populations of peteinoid acritarchs recovered from Middle Ordovician strata of the Hälludden and Horns Udde quarry sections (Öland, Sweden) allows for statistical analyses based on morphometric measurements. The results indicate the presence of assemblages with a continuous variability of morphotypes, thus a distinction of di...

The latitudinal diversity gradient (LDG) — the decline in species richness from the equator to the poles — is classically considered as the most pervasive macroecological pattern on Earth, but the timing of its establishment, its ubiquity in the geological past, and explanatory mechanisms remain uncertain. By combining empirical and modeling approa...

Data from a new comprehensive macrofossil-based compilation of early plant genera are analyzed via a Q-mode factor analysis. This compilation ranges from the Silurian to the earliest Carboniferous and illustrates the key vegetation changes that took place during the configuration of early terrestrial ecosystems. Results reveal that four factors can...

This study documents ‘colonial’ palynomorphs from the Upper Ordovician Ghelli Formation of northeastern Iran. The aggregates of organic–walled microfossils come from the Katian Armoricochitina nigerica - Ancyrochitina merga chitinozoan biozones of this formation. The ‘colonial’ microfossils can be classified as acritarchs and/or cryptospores, but t...

The Pin Formation of the northern Indian Himalaya may contain a record of the late Katian (Late Ordovician) warming event (the Boda Event). Palynological samples collected from two members of this formation are investigated in order to evaluate the biostratigraphical potential of the different microfossil groups. Acritarchs and chitinozoans are the...

The oldest sediments of the Traras Mountains in northwestern Algeria have been analyzed palynologically. Several levels of the 'Formation des Psammites bioturbés' provide few specimens of poorly preserved acritarchs, that nevertheless allow a stratigraphic attribution of the investigated section to the Middle to Upper Ordovician, due to the presenc...

A detailed palynological study was conducted in the lower Palaeozoic of the Zagros Basin (southwestern Iran) where the Mila and Ilbeyk formations are present in several areas. The Mila Formation mainly consists of dolostones, limestones and shales deposited in a shallow marine to outer ramp environment. It is conformably overlain by the Ilbeyk Form...

After its first description in Cambrian–Ordovician boundary strata from Gondwana, the acritarch genus Vulcanisphaera Deunff, 1961 has been found subsequently on most other paleocontinents, with total 32 species assigned to this genus. A comprehensive revision of the published literature indicates that the genus contains only three species that are...

The acritarch genus Orthosphaeridium Eisenack 1968 is one of the most frequently recorded acritarch taxa in the Ordovician. The taxonomy of this easily recognizable genus is revised herein based on a detailed literature review and on new investigations of palynological material from northeastern Iran and South China. The review confirms that Baltis...

Sedimentary organic matter (OM) is a major reservoir of organic carbon in the global carbon cycle. Despite many studies, there still exist many debates on the mechanism of OM accumulation and preservation in marine sediments. We present a new field study of a Lower Cambrian shallow marine shelf sequence in the northern edge of the Yangtze Plate, Ch...

Upper Darriwilian to middle Katian (Ordovician) outcrops are well exposed in the Kalpin (Aksu) area, in the northwestern margin of the Tarim Basin, Xinjiang, China. The Dawanxigou and Sishichang sections in the Kalpin area, near the Dawangou Auxiliary Stratotype Section and Point (ASSP), were palynologically investigated. Both sections provide well...

A review of biodiversity curves of marine organisms indicates that, despite fluctuations in amplitude (some large), a large-scale, long-term radiation of life took place during the early Palaeozoic Era; it was aggregated by a succession of more discrete and regionalized radiations across geographies and within phylogenies. This major biodiversifica...

Recent molecular clock data suggest with high probability a Cambrian origin of Embryophyta (also called land plants), indicating that their terrestrialization most probably started about 500 Ma. The fossil record of the ‘Cambrian Explosion’ was limited to marine organisms and not visible in the plant fossil record. The most significant changes in e...

Recent molecular clock data suggest with highest probability a Cambrian origin of Embryophyta (also called land plants), indicating that their terrestrialization most probably started about 500 million years ago. The fossil record of the ‘Cambrian explosion’ was limited to marine organisms and not visible in the plant fossil record. The most signif...

The acritarch genus Saharidia Combaz 1967 was originally described from the subsurface of the Algerian Sahara. It has been frequently recorded from late Cambrian and Early Ordovician sediments worldwide. A total of nine species have been attributed to the genus. In the present study Saharidia is revised in detail, based on a literature review and o...

The Hungshihyen Formation represents the Lower to Middle Ordovician near-shore siliciclastic deposits on the western margin of the Yangtze Platform, South China. However, its age is still debated, largely because of insufficient studies. Here we documented the Bursachitina maotaiensis–B. qianbeiensis chitinozoan assemblage from the lower part of th...

There are few publications on the precise age and palaeogeography of the Palaeozoic rocks of Colombia. In the present study the Pluspetrol Paisa-1 well, located in the central part of the Colombian Llanos Orientales Basin, is investigated palynologically, in order to determinate the age, the palaeoenvironment and the palaeogeography of the sediment...

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 ph...

Two major, extended diversifications punctuated the evolution of marine life during the Early Palaeozoic. The interregnum, however, between the Cambrian Explosion and the Great Ordovician Biodiversification Event, is exemplified by the Furongian Gap when there was a marked drop in biodiversity. It is unclear whether the gap is apparent, due to samp...

The marine fossil record shows five mass extinctions at the Ordovician–Silurian, Frasnian–Famennian (Late Devonian), Permian–Triassic, Triassic–Jurassic and Cretaceous–Palaeogene transitions. However, only one of these significantly disrupted plant evolution. We clearly need to look again at what we really mean by mass extinctions events, especiall...

The Permian-Triassic boundary (PTB) at ~252 Ma coincided with the largest mass extinction of the Phanerozoic. Previous research on diversity and abundance changes during this event has focused mainly on the terrestrial vertebrate and marine invertebrate records, with little attention to date given to the phytoplankton that form the base of the mari...

Dinoflagellates are part of the marine plankton and about 200 species produce a cyst (dinocyst) during their life cycle, these organic-walled sexually-produced cysts being fossilizable in sediments for hundreds of millions of years. Over the past 40–50 years, dinocysts have led to major advances on Mesozoic-Cenozoic research, in terms of biostratig...

Chitinozoans are widespread microfossils in the Ordovician to Devonian strata. Although they have been widely adopted in biostratigraphy, their environmental preferences are rarely discussed. In this study, the palaeoecological distribution of four Floian and Dapingian key chitinozoans in six coeval stratigraphical units based on 13 sections from t...

The classification of acritarchs remains a major problem concerning the study of this group, which is considered as representing a major part of the organic-walled phytoplankton of the Palaeozoic. It can be assumed that a large part of the taxa described in literature are not real biological entities but rather represent different (eco-) phenotypes...

The fossil record indicates that vascular plant diversity followed five different but complementary dynamics through the Phanerozoic Eon, the so-called Evolutionary Floras. Those floras reflect major transitions of plant evolution, from the earliest undoubted occurrences of vascular plants in the macrofossil record (tracheophytes; mid-Silurian time...

While their biological affinities remain enigmatic (by definition), many Palaeozoic acritarchs are considered to represent cysts of organic-walled microphytoplankton. Due to the often purely descriptive approach of many earlier studies, neglecting the palaeoecological context, it can be argued that a large part of the described acritarch taxa are n...

Palaeozoic beds from Colombia have been mainly recorded in outcrops from the Magdalena Valley, the Central Cordillera, the Eastern Cordillera and the Amazonian area. However, the Colombian Llanos Orientales Basin also displays an extensive Palaeozoic sedimentarysequence in its subsurface, especially of Ordovician, Devonian and Carboniferous age (e....

The Fezouata Lagerstätte, discovered in the Lower Ordovician rocks of Morocco, is a Konservat-Lagerstätte of prime scientific importance. It provides access not only to the ‘shelly’ (skeletonized) part of its fossil assemblages, but also to non-biomineralized to lightly sclerotized organisms and to exceptionally preserved soft tissues of a complex...

We introduce and briefly summarize a collection of papers contextualizing the onset of the Great Ordovician Biodiversification Event, initiated during the first meeting of IGCP project 653 at Van Mildert College, Durham University, UK, in September 2016.

Acritarchs and prasinophytes have generally been considered as organic-walled phytoplankton, and their distribution patterns play a significant role in palaeogeographical and palaeoclimatical reconstructions. In this paper the palaeobiogeography of Late Devonian phytoplankton (mainly Famennian) is quantitatively analyzed based on a global database...

This study focuses on the thermal maturity assessment of Silurian-Devonian sediments from the Ghadamis Basin, North Africa, comparing optical and geochemical analyses of palynomorphs. In southern Tunisia, the investigated subsurface cored section comprises the Argiles Principales Formation of Silurian age. In Libya, the succession studied covers th...

The Ordovician biodiversification has been recognized since the 1960s; the term ‘The Great Ordovician Biodiversification Event’, abbreviated by many as the ‘GOBE’, has been used for the past 20 years. The conceptual development and terminology applied to this crucial episode in marine life signify its considerable complexity. The GOBE includes succ...

The triangular-shaped acritarch genus Frankea, which displays characteristically branched appendices, has considerable stratigraphical and palaeobiogeographical significance in the Ordovician. High intraspecific variability of terminal processes (appendices) numbers and process lengths within Frankea suggest that the genus could be suitable for use...

The Global Stratotype Section and Point (GSSP) for the Lower Ordovician Floian Stage is defined by the first appearance datum (FAD) of the graptolite Tetragraptus approximatus at Diabasbrottet Quarry, Hunneberg, southern Sweden. Correlation of sections with the Floian GSSP when graptolites are absent, however, must rely on other criteria. Among oth...

Two new acritarch genera (Gordonirundum, Nirundella), three new species (Gordonirundum tungustanum, Gordonirundum? solidum, Nirundella baykitensis) and five new varieties (Gordonirundum tungustanum var. tungustanum autonym, G. tungustanum var. minutum, G. tungustanum var. tenuivertum, Nirundella baykitensis autonym, N. baykitensis var. ramusculosa)...

The Ordovician acritarch genus Barakella Cramer & Díez 1977 and two species, B. felix and B. fortunata, bearing characteristic anastomosing filamentous elements at one pole were first described from the subsurface of the Kasba Tadla Basin, Morocco. Subsequently, another species was described from the South Chinese Ordovician and was later attribute...

Various authors have described and illustrated exceptionally large acritarchs from the Furongian (upper Cambrian) from different parts of the world. The different morphotypes clearly belong to the ‘diacromorph’ acritarchs, but have until now usually been attributed, tentatively or erroneously, to the genus Veryhachium. Based on new material from th...

The so-called Big Five mass extinctions of the Phanerozoic include two prominent Palaeozoic episodes: the end-Ordovician and end-Permian events, both with large biodiversity loss. We consider that the end-Ordovician (Hirnantian) extinction could be best compared to the Middle Permian end-Guadalupian (=Capitanian) extinction, rather than to the end-...

First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species a...

Following the appearance of numerous animal phyla during the ‘Cambrian Explosion’, the ‘Great Ordovician Biodiversification Event’ (GOBE) records their rapid diversification at the lower taxonomic levels, constituting the most significant rise in biodiversity in Earth's history. Recent studies suggest that the rapid rise in phytoplankton diversity...

The lowest Ordovician (Tremadocian) chitinozoan biostratigraphy of the South China Palaeoplate has been reviewed and updated, based on new investigation from the Upper Yangtze area. The systematic paleontology of Lagenochitina pestovoensis Obut 1973 and Lagenochitina destombesi Elaouad-Debbaj 1988, has been revised. Previous identifications of L. d...

The Middle Ordovician (Darriwilian) Winneshiek Shale from Winneshiek County, Iowa, USA, hosts a Konservat-Lagerstätte that has yielded a diverse fauna including soft-bodied fossils. The shale is rich in organic content; in particular, algal material and fragmentary cuticular remains. Palynological acid treatment alongside modified, low-manipulation...

Three significant mass extinctions and five mass depletions in biodiversity are currently accepted in the Phanerozoic marine fossil record. While some of these marine biodiversity crises seem to correspond to important extinctions on land it is unclear if the dynamics are always similar. Here we compare the trajectories of marine and terrestrial li...

Previous studies on the Darriwilian (Middle Ordovician) Konservat-Lagerstätte of the Winneshiek Shale in Iowa (USA) have reported various animal and trace fossils. A search for “small carbonaceous fossils” (SCFs) in palynological samples from the Winneshiek Shale has now led to the discovery of several different kinds of organic-walled microfossils...