Silurian Research Papers - Academia.edu (original) (raw)

New millipede specimens from the Paleozoic of Scotland are described, including Archidesmus macnicoli , from the Lower Devonian (Lochkovian) Tillywhandland Quarry SSSI and three new taxa—Albadesmus almondi, Pneumodesmus newmani, and... more

New millipede specimens from the Paleozoic of Scotland are described, including Archidesmus macnicoli , from the Lower Devonian (Lochkovian) Tillywhandland Quarry SSSI and three new taxa—Albadesmus almondi, Pneumodesmus newmani, and Cowiedesmus eroticopodus—from the mid Silurian (late Wenlock—early Ludlow) Cowie Formation at Cowie Harbour. Cowiedesmus eroticopodus new species is placed within the new Cowiedesmidae within the new order Cowiedesmida. Kampecaris tuberculata Brade-Birks from the Lower Devonian (Siegenian) of the Lanark Basin near Dunure is shown not to be a kampecarid myriapod, redescribed as Palaeodesmus tuberculata and placed order incertae sedis within Archipolypoda. Anthracodesmus macconochiei Peach is also redescribed and tentatively placed order incertae sedis within Archipolypoda. Archidesmus macnicoli, Albadesmus almondi, and Palaeodesmus tuberculata are each demonstrated to have broad sternites with laterally placed coxal sockets and paramedian pores containing paired valves. These pores are interpreted as having housed eversible vesicles. Some specimens of Archidesmus macnicoli and Cowiedesmus eroticopodus are male and have a pair of modified legs on trunk segment 8, identified as leg pairs 10 and 11, respectively. The presence of modified anterior legs restricted to segment 8 increases the range of variability known in modified appendage location in male millipedes and compounds existing uncertainty about using the presence of gonopods on trunk segment 7 as a synapomorphy of Helminthomorpha. An affinity between Archidesmida and Cowiedesmida is suggested based on possession of modified legs on segment 8 and Archidesmida + Cowiedesmida is placed along with Euphoberiida in Archipolypoda based on possession of free, broad sternites with bivalved paramedian pores and fused pleurotergites. The oldest known evidence of spiracles is demonstrated in Pneumodesmus newmani, proving that the oldest known millipedes were fully terrestrial.

During these last years, considerable attention has been given to unconventional oil and gas shale in northern Africa where the most productive Paleozoic basins are located (e.g. Berkine, Illizi, Kufra, Murzuk, Tindouf, Ahnet, Oued Mya,... more

During these last years, considerable attention has been given to unconventional oil and gas shale in northern Africa where the most productive Paleozoic basins are located (e.g. Berkine, Illizi, Kufra, Murzuk, Tindouf, Ahnet, Oued Mya, Mouydir, etc). In most petroleum systems, which characterize these basins, the Silurian played the main role in hydrocarbon generation with two main ‘hot’ shale levels distributed in different locations (basins) and their deposition was restricted to the Rhuddanian (Lllandovery: early Silurian) and the Ludlow-Pridoli (late Silurian). A third major hot shale level had been identified in the Frasnian (Upper Devonian). Southern Tunisia is characterized by three main Paleozoic sedimentary basins, which are from North to South, the southern Chotts, Jeffara and Berkine Basin. They are separated by a major roughly E-W trending lower Paleozoic structural high, which encompass the Mehrez-Oued Hamous uplift to the West (Algeria) and the Nefusa uplift to the East (Libya), passing by the Touggourt-Talemzane-PGA-Bou Namcha (TTPB) structure close to southern Tunisia. The forementioned major source rocks in southern Tunisia are defined by hot shales with elevated Gamma ray values often exceeding 1400 API (in Hayatt-1 well), deposited in deep water environments during short lived (c. 2 Ma) periods of anoxia. In the course of this review, thickness, distribution and maturity maps have been established for each hot shale level using data for more than 70 wells located in both Tunisia and Algeria. Mineralogical modeling was achievd using Spectral Gamma Ray data (U, Th, K), SopectroLith logs (to acquire data for Fe, Si and Ti) and Elemental capture Spectroscopy (ECS). The latter technique provided data for quartz, pyrite, carbonate, clay and Sulfur. In addition to this, the Gamma Ray (GR), Neutron Porosity (ΦN), deep Resistivity (Rt) and Bulk Density (ρb) logs were used to model bulk mineralogy and lithology. Biostratigraphic and complete geochemical review has been undertaken from published papers and unpublished internal reports to better assess these important source intervals.

Some proetid cranidia and free cheeks with affinities to Proetus verrucosus Lindstroem, 1885 are reported from Wenlockian glacial erratics of the Laerheide area (County of Osnabrück, NW-Germany). A new species, Proetus leprosus n. sp.,... more

Some proetid cranidia and free cheeks with affinities to Proetus verrucosus Lindstroem, 1885 are reported from Wenlockian glacial erratics of the Laerheide area (County of Osnabrück, NW-Germany). A new species, Proetus leprosus n. sp., characterized by a subcylindrical or conical truncated glabella and a coarse nodular exoskeletal sculpture, is described. Cranidia of Proetus cf. verrucosus Lindstroem and Proetus cf. concinnus (Dalman, 1827), occurring together in a glacial erratic boulder, are documented.

During the past three decades, early vertebrates from the mid-Paleozoic of China have attracted extensive attention on account of their distinctive anatomical features, high diversity, early stratigraphic occurrence, and paleogeographic... more

During the past three decades, early vertebrates from the mid-Paleozoic of China have attracted extensive attention on account of their distinctive anatomical features, high diversity, early stratigraphic occurrence, and paleogeographic significance. These new findings have considerably increased our knowledge of vertebrate diversity, helped clarify the interrelationship of early fishes, and provided important data for mid-Paleozoic biostratigraphy and biogeography. In this paper, six Siluro-Devonian vertebrate faunas from China (Xiaoxiyu, Xiaoxiang, Xitun, Jiucheng, Haikou, and Zhongning faunas) and related stratigraphic problems are discussed. Biogeographically, the three main Chinese blocks (South China, North China, and Tarim blocks) constitute the “Pan-Cathaysian Galeaspid Province” during the mid-Paleozoic with highly endemic vertebrate faunas. Some major groups of early vertebrates, such as galeaspids, placoderms, and sarcopterygians, apparently originated and diversified in China. We suggest that three dispersal routes of early vertebrates (Northern Route, Southern Route, and Circum-Panthalassic Ocean Route) bridged the Chinese blocks with the adjacent continents or blocks during the mid-Paleozoic.

The research of Silurian vertebrates in China is reviewed. Early vertebrates including galeaspids, thelodonts, placoderms, chondrichthyans, acanthodians and osteichthyans occur widely in the Silurian deposits of South China and Tarim.... more

The research of Silurian vertebrates in China is reviewed. Early vertebrates including galeaspids, thelodonts, placoderms, chondrichthyans, acanthodians and osteichthyans occur widely in the Silurian deposits of South China and Tarim. Seven assemblages are established for biostratigraphic correlation. They are Dayongaspis - Kalpinolepis - Sinacanthus assemblage (early Telychian, Llandovery), Hanyangaspis guodingshanensis - Sinacanthus assemblage (Iate Telychian, Llandovery), Sinogaleaspis - Xiushuiaspis - Sinacanthus assemblage (Sheinwoodian, Wenlock), Thelodus sinensis assemblage (Homerian, Wenlock), Silurolepis assemblage (Gorstian, Ludlow), Ligulalepis yunnanensis assemblage (Ludfordian, Ludlow), and Nostolepis sinica assemblage (Pridoli).

A new arthropod, Enalikter asphon gen. et sp. nov., is described from the Silurian (Wenlock Series) Herefordshire Lagerstatte of the UK. It belongs to the Megacheira (=short-great-appendage group), which is recognized here, from the first... more

A new arthropod, Enalikter asphon gen. et sp. nov., is described from the Silurian (Wenlock Series) Herefordshire Lagerstatte of the UK. It belongs to the Megacheira (=short-great-appendage group), which is recognized here, from the first time, in strata younger than mid-Cambrian age. Discovery of this new Silurian taxon allows us to identify a Devonian megacheiran representative, Bundebachiellus giganteus from the Hunsruck Slate of Germany. The phylogenetic position of megacheirans is controversial: they have been interpreted as stem chelicerates, or stem euarthropods, but when Enalikter and Bundenbachiellus to the most comprehensive morphological dataset available, a stem euarthropod position is supported, it falls in the sister clade to the crown-group euarthropods, and it provides new insights surrounding the origin and early evolution of the euarthropods. Recognition of Enalikter and Bundenbachiellus as megacheirans indicates that this major arthropod group survived for nearly 100 Myr beyond the mid-Cambrian.

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further... more

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

This map folio should be referenced as: Scotese, C.R., 2013. Map Folio 76 Early Silurian early Llandovery, 439.8 Ma), PALEOMAP PaleoAtlas for ArcGIS, volume 5, Early Paleozoic Paleogeographic, Paleoclimatic and Plate Tectonic... more

This map folio should be referenced as:
Scotese, C.R., 2013. Map Folio 76 Early Silurian early Llandovery, 439.8 Ma), PALEOMAP PaleoAtlas for ArcGIS, volume 5, Early Paleozoic Paleogeographic, Paleoclimatic and Plate Tectonic Reconstructions, PALEOMAP Project, Evanston, IL.
Also see: Scotese, C.R., 2014. Atlas of Silurian and Middle-Late Ordovician Paleogeographic Maps (Mollweide Projection), Maps 73 – 80, Volumes 5, The Early Paleozoic, PALEOMAP Atlas for ArcGIS, PALEOMAP Project, Evanston, IL. https://www.academia.edu/16744278/Atlas_of_Silurian_and_Middle-Late_Ordovician_Paleogeographic_Maps
Introduction
These maps (rectilinear projection) are from the PALEOMAP PaleoAtlas for ArcGIS (Scotese, 2013a-f). This is a digital atlas of plate tectonic, paleogeographic, and paleoclimatic reconstructions designed for use with the GIS software, ArcMap (ESRI). Table 1 lists the various types of maps that comprise the PALEOMAP PaleoAtlas. The maps included in this folio are highlighted in bold text (Table 1).
The last map in each folio is a rectilinear graticule that can be overlain on the maps to provide a geographic reference frame. A rectilinear projection was used because it can be easily georeferenced in ArcMap and transformed into a variety of other map projections. The rectilinear map projection can also be directly “wrapped” onto a spherical projection, like the oneused by Google Earth. A set of Google Earth paleoglobes has made from the maps in this folio. These Google Earth paleoglobes can be downloaded at: www.globalgeology.com.
If the map you need is missing, or if there doesn’t seem to be a map folio for the exact time interval of interest, please contact me (cscotese@gmail.com). Table 2 lists all the time intervals that comprise the PALEOMAP PaleoAtlas for ArcGIS. The PaleoAtlas contains one map for every stage in the Phanerozoic, as well as 6 maps for the late Precambrian. Eventually, Map Folios, like this one, will be published for every time interval in the PALEOMAP PaleoAtlas. The following section is a brief description of the maps that makeup the Map Folio.

A new dataset of the highest quality specimens of fully articulated, juvenile and mature exoskeletons of the Czech middle Silurian trilobite Aulacopleura koninckii offers improved resolution of original morphology by all measures... more

A new dataset of the highest quality specimens of fully articulated, juvenile and mature exoskeletons of the Czech middle Silurian trilobite Aulacopleura koninckii offers improved resolution of original morphology by all measures considered. The degree of variation in both size and shape among later meraspid instars was constant, and suggesting targeted growth in both attributes. Size-related changes in the shape of the dorsal exoskeleton and of the segment-invariant cephalon were detected in the meraspid stage, but in the holaspid phase marked allometry was detected only in the trunk region, with the pygidium showing notable expansion in relative size. Meraspid cranidial allometry was subtle, with significant changes in instar form detectable only after several molts. This trilobite developed gradually throughout meraspid and holaspid ontogeny, with the synchronous cessation of trunk segment appearance and release at the onset of the holaspid phase. Precise development of shape and size occurs in the context of marked variability in the number of trunk segments at maturity, illustrating complex patterns of character variation within a species. A new systematic description establishes the synonymy of several subspecies with A. koninckii.

May, A. (1989c): Die ältesten Gesteine des Sauerlandes und ihre Fossilien. - Der Märker, 38 (6): 258-265, 3 figs., pl. 1; Lüdenscheid. In diesem Artikel werden die Schichten des Ordoviziums, Silurs und tiefsten Devons (und ihre... more

The discovery of Entelognathus revealed the presence of maxilla, premaxilla, and dentary, supposedly diagnostic osteichthyan bones, in a Silurian placoderm. However, the relationship between these marginal jaw bones and the gnathal plates... more

The discovery of Entelognathus revealed the presence of maxilla, premaxilla, and dentary, supposedly diagnostic osteichthyan bones, in a Silurian placoderm. However, the relationship between these marginal jaw bones and the gnathal plates of conventional placoderms, thought to represent the inner dental arcade, remains uncertain. Here we report a second Silurian maxillate placoderm, which bridges the gnathal and maxillate conditions. We propose that the maxilla, premaxilla, and dentary are homologous to the gnathal plates of placoderms and that all belong to the same dental arcade. The gnathal-maxillate transformation occurred concurrently in upper and lower jaws, predating the addition of infradentary bones to the lower jaw.

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further... more

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

Silurian (Llandovery-Ludlow) Encrinurinae from Wisconsin, Indiana, and Illinois include species of Balizoma Holloway, 1980, Curiella Lamont, 1978, Distyrax Lane, 1988, Encrinurus Emmrich, 1844, Mackenziurus Edgecombe and Chatterton,... more

Silurian (Llandovery-Ludlow) Encrinurinae from Wisconsin, Indiana, and Illinois include species of Balizoma Holloway, 1980, Curiella Lamont, 1978, Distyrax Lane, 1988, Encrinurus Emmrich, 1844, Mackenziurus Edgecombe and Chatterton, 1990a, and Nucleurus Ramsköld, 1986. Mackenziurus lauriae n. sp. is described from Wenlock strata of the Racine and Sugar Run Dolomites; nine segments in the holaspid thorax are the fewest known for any encrinurid. A square rostral plate is diagnostic of Mackenziurus. New morphological data are provided by Illinois specimens of Balizoma indianensis (Kindle and Breger, 1904) from the Wenlock-Ludlow Racine Dolomite, and of Curiella tuberculifrons (Weller, 1907) from the Llandovery Elwood-Wilhelmi Formations. Nucleurus n. sp. is possibly from Llandovery strata of Wisconsin. Distyrax n. sp. occurs in the Brandon Bridge Member (late Llandovery-early Wenlock) of the Joliet Dolomite in Illinois. The type pygidia and possible topotype material of Encrinurus nereus Hall, 1867, confirm assignment to that genus as currently viewed; this reefal species is distinct from the closely related inter-reef species E. egani Miller, 1880, and appears to be distinct from reefal E. reflexus Raymond, 1916. Lectotypes are selected for those Encrinurus species.

This map folio should be referenced as: Scotese, C.R., 2013. Map Folio 75 Early Silurian late Llandovery, 432.1 Ma), PALEOMAP PaleoAtlas for ArcGIS, volume 5, Early Paleozoic Paleogeographic, Paleoclimatic and Plate Tectonic... more

This map folio should be referenced as:
Scotese, C.R., 2013. Map Folio 75 Early Silurian late Llandovery, 432.1 Ma), PALEOMAP PaleoAtlas for ArcGIS, volume 5, Early Paleozoic Paleogeographic, Paleoclimatic and Plate Tectonic Reconstructions, PALEOMAP Project, Evanston, IL.
Also see: Scotese, C.R., 2014. Atlas of Silurian and Middle-Late Ordovician Paleogeographic Maps (Mollweide Projection), Maps 73 – 80, Volumes 5, The Early Paleozoic, PALEOMAP Atlas for ArcGIS, PALEOMAP Project, Evanston, IL. https://www.academia.edu/16744278/Atlas_of_Silurian_and_Middle-Late_Ordovician_Paleogeographic_Maps
Introduction
These maps (rectilinear projection) are from the PALEOMAP PaleoAtlas for ArcGIS (Scotese, 2013a-f). This is a digital atlas of plate tectonic, paleogeographic, and paleoclimatic reconstructions designed for use with the GIS software, ArcMap (ESRI). Table 1 lists the various types of maps that comprise the PALEOMAP PaleoAtlas. The maps included in this folio are highlighted in bold text (Table 1).
The last map in each folio is a rectilinear graticule that can be overlain on the maps to provide a geographic reference frame. A rectilinear projection was used because it can be easily georeferenced in ArcMap and transformed into a variety of other map projections. The rectilinear map projection can also be directly “wrapped” onto a spherical projection, like the oneused by Google Earth. A set of Google Earth paleoglobes has made from the maps in this folio. These Google Earth paleoglobes can be downloaded at: www.globalgeology.com.
If the map you need is missing, or if there doesn’t seem to be a map folio for the exact time interval of interest, please contact me (cscotese@gmail.com). Table 2 lists all the time intervals that comprise the PALEOMAP PaleoAtlas for ArcGIS. The PaleoAtlas contains one map for every stage in the Phanerozoic, as well as 6 maps for the late Precambrian. Eventually, Map Folios, like this one, will be published for every time interval in the PALEOMAP PaleoAtlas. The following section is a brief description of the maps that makeup the Map Folio.

Sporangia, with their in situ cryptospores, spore masses, and a possible axis were identified in marginal marine Ludlovian deposits from Gotland, Sweden by means of light- and scanning electron microscopy.The sporangia identified are... more

Sporangia, with their in situ cryptospores, spore masses, and a possible axis were identified in marginal marine Ludlovian deposits from Gotland, Sweden by means of light- and scanning electron microscopy.The sporangia identified are elongate, with fragments of the sporangia covering preserved, and contain well-preserved in situ embryophyte cryptospores identified as Laevolancis divellomedia (monad) and Dyadospora murusdensa (dyad). A single detached axis was identified possessing superficial longitudinal striations resembling epidermal cell patterning. The axis ends in a cup-shaped structure that possibly represents the basal part of a sporangium. Masses of cryptospore monads shrouded in amorphous organic material, most probably representing coprolites of terrestrial arthropods, were found in the same beds. The spores in these masses are degraded in sharp contrast to the excellent preservation of the dispersed and sporangia-hosted spores. The monad, L. divellomedia, a common local constituent of the dispersed microflora, was identified in the coprolites. This is the first report of undisputed Silurian land plant remains in Baltica and the study reveals one of the earliest examples of arthropod–plant interactions.► Sporangia, spore masses, and an axis, from Gotland are described. ► The sporangia identified are containing well-preserved in situ cryptospores. ► The material comes from Silurian sections on Gotland (Baltica). ► Coprolites from arthropods containing spores are also described. ► The results are linked to early land plant life and animal–plant interactions.

Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropod taxa, notably chelicerates. Although they are used to crush shells and masticate soft food items, the microstructure of these spines are... more

Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropod taxa, notably chelicerates. Although they are used to crush shells and masticate soft food items, the microstructure of these spines are relatively poorly known in both extant and extinct forms. Here we compare the gnathobasic spine microstructures of the Silurian eurypterid Eurypterus tetragonophthalmus from Estonia and the Cambrian artiopodan Sidneyia inexpectans from Canada with those of the Recent xiphosuran chelicerate Limulus polyphemus to infer potential variations in functional morphology through time. The thickened fibrous exocuticle in L. polyphemus spine tips enables effective prey mastication and shell crushing, while also reducing pressure on nerve endings that fill the spine cavities. The spine cuticle of E. tetragonophthalmus has a laminate structure and lacks the fibrous layers seen in L. polyphemus spines, suggesting that E. tetragonophthalmus may not have been capable of crushing thick shells, but a durophagous habit cannot be precluded. Conversely, the cuticle of S. inexpectans spines has a similar fibrous microstructure to L. polyphemus, suggesting that S. inexpectans was a competent shell crusher. This conclusion is consistent with specimens showing preserved gut contents containing various shelly fragments. The shape and arrangement of the gnathobasic spines is similar for both L. polyphemus and S. inexpectans, with stouter spines in the posterior cephalothoracic or trunk appendages, respectively. This differentiation indicates that crushing occurs posteriorly, while the gnathobases on anterior appendages continue mastication and push food towards and into the mouth. The results of recent phylogenetic analyses that considered both modern and fossil euarthropod clades show that xiphosurans and eurypterids are united as crown-group euchelicerates, with S. inexpectans placed within more basal artiopodan clades. These relationships suggest that gnathobases with thickened fibrous exocuticle, if not homoplasious, may be plesiomorphic for chelicerates and deeper relatives within Arachnomorpha. This study shows that the gnathobasic spine microstructure best adapted for durophagy has remained remarkably constant since the Cambrian.

An assemblage of earliest Silurian (Llandovery, Rhuddanian) fossils from South Kazakhstan (Ak-Kerme Peninsula, Lake Balkhash) contains solitary rugose corals (Calostylis denticulata, Streptelasma? sp., and Cystipaliphyllum sp.) and the... more

An assemblage of earliest Silurian (Llandovery,
Rhuddanian) fossils from South Kazakhstan (Ak-Kerme
Peninsula, Lake Balkhash) contains solitary rugose corals (Calostylis denticulata, Streptelasma? sp., and Cystipaliphyllum sp.) and the demosponge Calycocoelia typicalis, which are described here. This assemblage occurs with previously described brachiopods and constitutes a post extinction survival fauna; such faunas are poorly known and this study fills a gap in our knowledge. All three genera of Rugosa were transitional across the Ordovician–Silurian boundary and are also reported from other parts of Kazakhstan,
Uzbekistan, and Tajikistan during the Llandovery.
Streptelasma had already been present in Kazakhstan during the Ordovician, while during the Rhuddanian Calostylis immigrated from Baltica or China, and Cystipaliphyllum from the Australian part of Gondwana. Demosponges are rare during the Llandovery but probably had a cosmopolitan distribution. Calycocoelia typicalis marks the first Rhuddanian record of lithistid demosponges, and the first record of Silurian demosponges from Kazakhstan.

This map folio should be referenced as: Scotese, C.R., 2013. Map Folio 73 Late Silurian (Ludlow & Pridoli, 419.5 Ma), PALEOMAP PaleoAtlas for ArcGIS, volume 5, Early Paleozoic Paleogeographic, Paleoclimatic and Plate Tectonic... more

"The number of knownSilurian gnathostome fossils has increased significantly during the last two decades, and greatly improved our understanding of the early diversification of gnathostomes (jawed vertebrates). Primitive gnathostome... more

"The number of knownSilurian gnathostome fossils has increased significantly during the last two decades, and greatly improved our understanding of the early diversification of gnathostomes (jawed vertebrates). Primitive gnathostome remains from the Silurian of China are of special interest in bridging morphological gaps between osteichthyans and non-osteichthyan gnathostome groups. A review of these early fishes shows that gnathostomes had already obtained a wide distribution and experienced an early radiation in the Middle-Late Silurian.
Environmental conditions in the Silurian are inferred from recent advances in geochemistry and paleoclimate models. Atmospheric oxygen concentration, an environmental factor critical in organismal evolution, rose gradually during the Silurian and reached modern levels for the first time. Compared to the Middle Ordovician when invertebrates and agnathans underwent a great radiation, the Middle-Late Silurian is distinctive for its high atmospheric oxygen level. We suggest that the rise of the atmospheric oxygen concentration would have triggered the early radiation of jawed vertebrates in the Silurian, which paved the way for the high generic diversity of vertebrates in the Devonian.""

May, A. (1997c): Statistics on Thamnopora (Tabulata, Devonian). - In: Perejón, A., & Comas-Rengifo, M. J. [Eds.]: Proceedings of the VII International Symposium on Fossil Cnidaria and Porifera held in Madrid, Spain, 1995, Volume I,Boletín... more

A single specimen of a new species of the chasmata-spidid Diploaspis Størmer, 1972 is described from the upper Silurian (Pridoli) Phelps Member of the Fiddlers Green Formation (Bertie Group) in Herkimer County, New York State, USA.... more

A single specimen of a new species of the chasmata-spidid Diploaspis Størmer, 1972 is described from the upper Silurian (Pridoli) Phelps Member of the Fiddlers Green Formation (Bertie Group) in Herkimer County, New York State, USA. Diploaspis praecursor sp. nov. is distinguished by the shape of the posterolateral margins of the buckler, which are drawn out into angular epimera, and by the lack of elongate tubercles on the postabdomen. This discovery increases the taxonomic diversity of the Bertie Group by extending the geographic extent of Diploaspididae into North America. D. praecursor pre-dates previously known species of Diploaspis by more than 10 million years.

Petrographic and calcrete carbon isotope data from seasonally waterlogged Upper Silurian (Přídolí) to Lower Devonian (Pragian) palaeo-V ertisols of the Old Red Sandstone, South Wales, UK, are presented. The δ13C values mostly range from... more

Petrographic and calcrete carbon isotope data from seasonally waterlogged Upper Silurian (Přídolí) to Lower Devonian (Pragian) palaeo-V ertisols of the Old Red Sandstone, South Wales, UK, are presented. The δ13C values mostly range from -9 to -12‰ (VPDB), suggesting the soils were inhabited by abundant vegetation that when oxidised (perhaps with microbial assistance) resulted in CO2-rich soils. Such soils would favour calcrete precipitation through equilibration of soil zone CO2 with the relatively lower atmospheric pCO2. However, reliably estimating palaeoatmospheric pCO2 calculated from these carbon isotope data is a challenge.

The biogeographical distribution of Ordovician and Silurian gastropods, monoplacophorans and mimospirids has been analysed on a generic level. The dataset contains 334 genera and 2769 species, yielding 1231 records of genera with 2274... more

The biogeographical distribution of Ordovician and Silurian gastropods, monoplacophorans and mimospirids has been analysed on a generic level. The dataset contains 334 genera and 2769 species, yielding 1231 records of genera with 2274 occurrences worldwide. There is a bias towards eastern Laurentia, Baltica and Perunica records. Some 53.1% of the records are Ordovician. The study demonstrates that these molluscs are well suited to being used to improve understanding of Ordovician and Silurian biogeographical provinciality. Specific points are that: a Lower Ordovician assemblage is evident in Laurentia; the fauna of the Argentinean Precordillera is Laurentian until the Darriwilian, when taxa are shared with North China; Late Silurian gastropods from the Alexander terrane (SE Alaska) are unknown in Laurentia, but support a rift origin of this terrane from NE Siberia; Perunica, Ibero-Armorica and Morocco cluster together throughout the Ordovician but Perunica and Morocco are closer; Darriwilian–Sandbian deep-water Bohemian taxa occur in Baltica; a Laurentian–Baltica proximity is unsupported until the Silurian; Siberia clusters with North China and eastern Laurentia during the Tremadocian–Darriwilian; during the Gorstian–Pridoli Siberia clusters with the Farewell and Alexander terranes; North China may have been close to Laurentia and the Argentinean margin of Gondwana; and the affinity of Tarim taxa is problematic.

During the last decade, exploration activities in the Ghadames Basin have been intensified by the National Oil Corporation (NOC), national, and international companies. Arabian Gulf Oil Company (AGOCO) was the leader in most of the... more

During the last decade, exploration activities in the Ghadames Basin have been intensified by the National Oil Corporation (NOC), national, and international companies. Arabian Gulf Oil Company (AGOCO) was the leader in most of the discovered fields in the basin by drilling numerous wildcat wells targeting siliciclastic Paleozoic reservoirs, mainly of Silurian age. The Silurian rock units are known to contribute both source rock (Tanezzuft) and hydrocarbon reservoir (Acacus) successions in the area. The Acacus Formation is subdivided informally into three main units known as lower, middle, and upper, with the lower unit containing the main reservoir potential. These units have been mapped using basic well log data, nevertheless their sedimentological criteria remained untapped due to operational issues such as cutting cores. It has been observed from the appraisal wells that there is a high uncertainty of the reservoir's lateral continuity even within a few kilometers distance. Therefore, there was a demand to understand the stratigraphic depositional architecture and its lateral continuity and distribution of the sandstone reservoir units in the area. By using basic well log data alone, it was a challenge for the geoscientists to identify the main lateral variations especially in cases where the core is not available. Accordingly, AGOCO has started a new acquisition plan to come up with high resolution sedimentological understanding of the main reservoir in the area. The exploration team decided to acquire two main wireline tools, those are, borehole images (FMI) which gives a resolution down to 5 mm as well as element capture spectroscopy (ECS) which gives quantitative results of the elements for optimum geological interpretation in a detailed scale. The advantage is having more than 900 ft of core-like description data of the Lower Acacus units as well as a quantitative elements computation. This has in return resulted in a high resolution of sedimentological and stratigraphic interpretation throughout the Lower Acacus clastic reservoir in the Ghadames Basin. Imaging the wellbore and measuring the dip of the features have retained vast knowledge for AGOCO about the vertical succession of the main reservoir and understanding the reservoir geometries. In this poster, a case study from one of AGOCO wells has illustrated the value of the comprehensive wellbore integration and interpretation. As a result, and based on the detailed

This study documents previously unknown tax-onomic and morphological diversity among early Palaeozoic crinoids. Based on highly complete, well preserved crown material, we describe two new genera from the Ordovician and Silurian of the... more

This study documents previously unknown tax-onomic and morphological diversity among early Palaeozoic crinoids. Based on highly complete, well preserved crown material, we describe two new genera from the Ordovician and Silurian of the Baltic region (Estonia) that provide insight into two major features of the geological history of crinoids: the early evolution of the flexible clade during the Great Ordovician Biodiversification Event (GOBE), and their diversification history surrounding the end-Ordovician mass extinction. The unexpected occurrence of a highly derived sagenocrinid, Tintinnabulicrinus estoniensis gen. et. sp. nov., from Upper Ordovician (lower Katian) rocks of the Baltic palaeocontinent provides high-resolution temporal , taxonomic and palaeobiogeographical constraints on the origin and early evolution of the Flexibilia. The Silurian (lower Rhuddanian, Llandovery) Paerticrinus arvosus gen. et sp. nov. is the oldest known Silurian crinoid from Baltica and thus provides the earliest Baltic record of crinoids following the aftermath of the end-Ordovician mass extinction. A Bayesian 'fossil tip-dating' analysis implementing the fossilized birth–death process and a relaxed morphological clock model suggests that flexibles evolved c. 3 million years prior to their oldest fossil record, potentially involving an ancestor–descendant relationship (via 'budding' cladogenesis or anagenesis) with the paraphyletic cladid Cupulocrinus. The sagenocrinid subclade rapidly diverged from 'tax-ocrinid' grade crinoids during the final stages of the GOBE, culminating in maximal diversity among Ordovician crinoid faunas on a global scale. Remarkably, diversification patterns indicate little taxonomic turnover among flexibles across the Late Ordovician mass extinction. However, the elimination of closely related clades may have helped pave the way for their subsequent Silurian diversification and increased ecological role in post-Ordovician Palaeozoic marine communities. This study highlights the significance of studies reporting faunas from undersampled palaeogeo-graphical regions for clade-based phylogenetic studies and improving estimates of global biodiversity through geological time.

Histological study of new specimens of sinacanth fìn spines from the Lower Silurian of the northwestern margin of the Tarim Basin (Xinjiang, China) shows that they have the same histology as the fìn spines of chondrichthyans. On this... more

Histological study of new specimens of sinacanth fìn spines from the Lower Silurian of the northwestern margin of the Tarim Basin (Xinjiang, China) shows that they have the same histology as the fìn spines of chondrichthyans. On this basis it is argued that sinacanths are one of the oldest known chondrichthyans, rather than acanthodians, and their spines are the oldest known shark fìn spines. Previous studies on sinacanths are critically reviewed. The family Sinacanthidae is erected to include Sinacanthus and its relatives with more than 15 fìn spine ridges per side. It is suggested that Sinacanthus fancunensis is synonmous with S. wuchangensis. A new sinacanth genus and species, Tarimacanthus bachuensis, from the Lower Silurian of Tarim and South China, is erected.

This study describes the largest known Palaeozoic boring trace, Osprioneides kampto igen. et isp. nov., found within a stromatoporoid Densastroma pexisum from the Upper Visby Formation (lower Wenlock, Silurian) on the island of Gotland,... more

This study describes the largest known Palaeozoic boring trace, Osprioneides kampto igen. et isp. nov., found within a
stromatoporoid Densastroma pexisum from the Upper Visby Formation (lower Wenlock, Silurian) on the island of
Gotland, Sweden. Differences between the physical properties of the stromatoporoid and the dense micritic infilling of
the borings allowed the application of the CT−scan technology for the 2D and 3D−visualisation of this rare trace. The addi−
tional application of a stereoscopic technique on these CT images and movies enhances its value for unravelling spatial
orientations. This non−destructive method has a great potential for future macro− as well as microboring analyses. The
trace maker, most likely a worm, infested the hosting colony post−mortem with up to 120 mm long borings measuring
5–17 mm in diameter. Smaller forms of Trypanites and Palaeosabella within the same stromatoporoid preferentially oc−
cur in the outer coenosteum and occasionally in abandoned borings of O. kampto. The stratigraphic position of O. kampto
follows the “Great Ordovician Biodiversification Event” in time, and reflects the increase in diversity of boring species.
Borings with penetration depths of 120 mm are, however, unique findings for the Palaeozoic and were not exceeded until
some 260 million years later (Bajocian, Middle Jurassic) when the “Mesozoic Marine Revolution” led to convergent
reinventions as a result of enhanced predation, grazing pressure, and ecospace competition.

Cyclocystoids are a poorly known, rare, extinct class of bi-facially flattened, disc shaped echinoderms, ranging from the Middle Ordovician to the Early Carboniferous. Articulated cyclocystoids are relatively common in the Ordovician but... more

Cyclocystoids are a poorly known, rare, extinct class of bi-facially flattened, disc shaped echinoderms, ranging from the Middle Ordovician to the Early Carboniferous. Articulated cyclocystoids are relatively common in the Ordovician but are rarer in younger strata. Here we describe Perforocycloides nathaliae new genus and species, from the early Silurian of Anticosti Island, Québec, Canada, the first articulated cyclocystoid from the Silurian of North America. This taxon is distinguished from other cyclocystoids by the number of variably sized marginal ossicles, the lack of interseptal plates, and the novelty of pores located in the distal part of the sutures between adjacent marginals on the dorsal surface. These dorsal intermarginal sutural pores led to canals which penetrated the contiguous area of the lateral surface of the marginals and emerged on the ventral surface between the cupules of adjacent marginals. These dorsal intermarginal sutural pores/canals appear to be unique to Perforocycloides and whilst their function is speculative, they provided some form of communication between the dorsal disc and the distal side of the ventral marginals/cupules. Perforocycloides most closely resembles the Ordovician-Silurian genus Zygocycloides, suggesting that this genus may have diversified more widely during the Silurian than previously reported. A review of global Silurian cyclocystoid distribution suggests taxa were geographically confined and that greatest diversity appears to have been located within Baltica. However, it also demonstrates our current limited knowledge. No specimens have been recorded from Gondwana (e.g. Africa, Australia, South America), Siberia, and North and South China, nor are any specimens known confidently anywhere from Přidolí strata.

Here we review the Silurian and Devonian vertebrates from Southeast Asia and their biogeographic affinities. These vertebrate remains are distributed in the Shan-Thai and Indochina terranes as well as the South China block, including the... more

Here we review the Silurian and Devonian vertebrates from Southeast Asia and their biogeographic affinities. These vertebrate remains are distributed in the Shan-Thai and Indochina terranes as well as the South China block, including the fossil fishes from western Yunnan (a part of the Shan-Thai terrane). The Devonian vertebrates from the Si Ka, Bac Bun and Mia Le formations of northern Vietnam resemble those from the Xitun Formation of Yunnan, South China, and thus belong to the Xitun fauna. The Late Silurian vertebrates from the Dia Giang Formation of My Duc (central Vietnam) are suggestive of the Xiaoxiang fauna of South China. Fossil vertebrate evidence shows the proximity between the South China block and the Indochina terrane in the Middle Palaeozoic and the close relationship between Shan-Thai and east Gondwana in the Middle Devonian.