A New Late Silurian or Early Devonian Thelodont from the Boothia Peninsula, Arctic Canada

Isolated scales of Boothialepis thorsteinssoni gen. et sp. nov. are described from a fossiliferous calcareous dolomite at the base of the Somerset Island Formation of the Boothia Peninsula, Arctic Canada. A new family, Boothialepididae (Thelodonti), is established on features of the scale morphology and histology. The new genus and species are distinguished by characteristics of crown sculpture, neck, and unusual size of the base. Two other thelodonts, Nikolivia elongata Karatajūtė-Talimaa and Canonia grossi Vieth, and an acanthodian, Poracanthodes sp., are described from the same stratigraphical level. Thelodonts have not previously been described from the Boothia Peninsula. Conodont-based correlation indicates a Late Silurian age for the base of the Somerset Island Formation on the Boothia Peninsula. Correlation of the beds with precisely dated microvertebrates in the Read Bay section on Cornwallis Island enables the age of the horizon with the new species to be determined as Early Devonian.     

An operculum of the Silurian nautiloid Aptychopsis from Arctic Canada

Three articulated valves of the genus Aptychopsis are interpreted as the operculum of a nautiloid. The valves are joined by an organic film which covers the entire dorsal valve. This genus has not been previously reported from North America.     

Upper Ordovician and Lower Silurian chitinozoans from central Nevada and Arctic Canada

Late Ordovician and Early Silurian chitinozoans from the uppermost Vinini Formation, and the Hanson Creek Formation in central Nevada and the lower Cape Phillips Formation, Cape Manning section, in Arctic Canada have been re-investigated and a new chitinozoan biozonation is proposed. The Upper Ordovician of central Nevada can easily be correlated to that of Arctic Canada through the common occurrence of the Ordochitina nevadensis biozone in both regions. No such correlation, however, is possible with the Late Ordovician of Anticosti Island in eastern Canada because of the absence of the index Upper Ordovician chitinozoan zonal species of central Nevada such as Belonechitina tenuispinata sp. nov, Ordochitina nevadensis sp. nov. and Nevadachitina vininica gen. nov., sp. nov. in the former area.One new genus, Nevadachitina, and nine new species, Eisenackitina ripae, Belonechitina martinica, Nevadachitina vininica, Nevadachitina praevininica, Ordochitina nevadensis, Belonechitina tenuispinata, Belonechitina parvispinata, Tanuchitina laurentiana, Angochitina hansonica are described and illustrated in this paper and four species are left in open nomenclature.     

Origin of the Retiolitidae: insights from a new graptolite genus from the early Silurian of Arctic Canada

Isolated specimens of Hercograptus introversus n. gen., n. sp. show features characteristic of the Retiolitidae, such as partial periderm reduction, and extended ancora lists and a reticulum that are attached to the thecal margins, on a rhabdosome that, in most other respects, resembles Pseudorthograptus. This newly discovered graptolite provides support for the hypothesis that Pseudoretiolites is the first-evolved retiolitid, since they share a similar ancora type and unique thecal style. It is also clear that the suite of features that normally distinguish the Retiolitidae did not all evolve simultaneously. It is proposed that development of a complete thecal framework of lists, permitting complete periderm reduction, should be the character used to distinguish the Retiolidae from the Petalolithidae. Unusual apertural modifications, such as strong introversion, lateral lappets, and a short, free dorsal wall suggest that Hercograptus may be an offshoot of the lineage leading from Pseudorthograptus to Pseudoretiolites.     

Late Silurian plant microfossil assemblage from Guangyuan,Sichuan, China

A dispersed plant microfossil assemblage is described from Late Silurian deposits from Guangyuan, Sichuan, China. These strata are interpreted as nearshore, shallow marine deposits, and brachiopods suggest a late Ludlow–early Pridoli age. The palynomorph assemblage is dominated by terrestrial forms, including cryptospores and trilete spores, tubular structures and cuticle-like sheets, although rare marine acritarchs are also present. This microfossil assemblage is comparable to coeval assemblages from around the world (South and Southwest Wales; Libya; Canada; Southeastern Turkey; Northwest Spain; and Jiangsu, China). The sporomorphs from this assemblage indicate the existence of early land plants during the late Ludlow–early Pridoli in Guangyuan, Sichuan, China; and suggests that floras of this age were cosmopolitan and exhibited little palaeogeographical differentiation.     

Peridermal and interthecal tissue in Silurian retiolitid graptolites: with examples from Sweden and Arctic Canada

Peridermal tissue, and thecal 'floors' are shown to be present in some specimens of Pseudoretiolites, Retiolites and Stomatograptus. The development of a dense reticulum and thecal hoods is also recognized as being a progressive developmental feature in Gothograptus. It is suggested that all these structures, whether internal or external, are the product of mature or old-age development. It appears questionable whether the Rhabdopleura model of rhabdosomal development adequately explains late-stage membranes and other adventitious tissues such as discussed herein.     

Fragmentary non-vascular plant microfossils from the late Silurian of Wales

A wide variety of cuticles and tubular elements is described from a late Silurian (Ludlow Series) locality in Wales which has already yielded a macroflora containing Cooksonia Lang, Steganotheca Edwards and vascularized axes. These microfossils are compared with Lang's Downtonian .Nematothallus complex and Silurian assemblages of similar composition from north America. It is concluded that the majority of these microfossils derive from non-vascular plants of uncertain affinity which lived on land.     

Late Silurian trilete spores from northern Jiangsu, China

The Late Silurian is generally considered to a particular significant key period in the study of early land vascular plants. A trilete spore assemblage of the Upper Silurian is described from northern Jiangsu, China. This assemblage comprises 11 genera and 20 species of trilete spores (including laevigate, apiculate, perinotrilite, patinate, rarely distally murornate and equatorially crassitate, and three indeterminate trilete miospores forms). It has similarities to those described from coeval assemblages from around the world (e.g., England and South Wales; Tripolitania, Libya; Cornwallis Island, Canadian Arctic; Northwest Spain). The rare cryptospore, only one specimen (Tetrahedraletes sp.) had been found to be associated with the Chinese trilete spore assemblage. The discovery of the trilete spores from Late Silurian rocks indicates the existence of early land plants, some possibly vascular, at that time in northern Jiangsu, China.     

The Early Silurian brachiopod Eocoelia from the Hudson Bay Basin, Canada

Eocoelia akimiskii sp. nov. from the Lower Silurian (upper Telychian) Attawapiskat Formation of Akimiski Island, James Bay, Nunavut, is the first and oldest Eocoelia to be described from the Hudson Bay Basin, one of three largest inland basins of North America. The new species lacks dental plates, dental cavities, and marginal deflection or lip, which indicates a post-Aeronian form of the well-known Eocoelia lineage. In rib numbers, Eocoelia akimiskii falls between E. curtisi and E. sulcata , being closer to E. sulcata . In rib strength, however, the new species is more closely allied to E. curtisi . Although Eocoelia is currently assigned to the Rhynchonellida because of its lack of spiralia, several features (particularly the lack of a septalium, the presence of a unique notothyrial platform and cardinal process, and dense, free-hanging fibrous growth frills) of the genus and other leptocoeliids are distinctly atypical of the rhynchonellides. The new species occurs in an inter-reef, shelly packstone facies within the Attawapiskat Formation, which is characterized by coral-stromatoporoid reefs with abundant, diverse, reef-dwelling brachiopods and other shelly organisms. The close association of Eocoelia akimiskii with the Attawapiskat reefs supports a shallow subtidal (BA2) setting generally assigned to the Eocoelia Community. The reefs themselves, however, host an extremely abundant brachiopod fauna dominated by Pentameroides , Trimerella , Septatrypa , and Gypidula . Four species of Clorinda are also common elements of the reef-dwelling brachiopods. This demonstrates that the concept of the classic Early Silurian level-bottom brachiopod communities cannot be directly applied to reef-dwelling brachiopod communities.     

Bryozoan palaeoecology in the Late Silurian of Gotland

The present paper deals with the ecology of the Bryozoa in the Upper Wenlockian of Gotland. The Upper Wenlockian sedimentary rocks of Gotland, locally known as the Halla-Mulde Beds, are deposited in a shallow sea. The sedimentary rock types include well-developed reefs of “barrier” and “fringing” types and marly limestones in both forereef and backreef positions. These sedimentary rocks are rich in Bryozoa as well as in other shelly fossils. Twenty seven bryozoan species have been identified from this stratigraphic sequence. The bryozoans tend to occur in associations. These are not strictly comparable with the neontological animal communities in the Petersen sense, but should rather be regarded as “ecozones”.Twelve different faunistic associations can be identified in the investigated material. On Bryozoa alone, five major zones are discernible.     

Late Silurian brachiopods from Darhan Mumingan Joint Banner, Inner Mongolia

Seven brachiopod species (including three new species) and three undetermined forms are described and figured here from an unnamed stratigraphic unit which mainly consists of argillaceous and bioclastic limestone near the stratotype of the Late Silurian Xibiehe Formation of the Xibiehe section in the Darhan Mumingan Joint Banner, north of the Bateaobao area, Inner Mongolia. Three new species, Eoschizophoria minuta, Navispira navicula and Howellella asiatica are established with transverse serial sections for their interiors. All brachiopod taxa described here show that this unnamed stratigraphic unit is higher than the Late Silurian Xibiehe Formation in the Xibiehe section and is possibly transitional between the Late Silurian and the Early Devonian. Authors temporarily regard this unit as the upper part of the Xibiehe Formation in this paper.     

Late Silurian trilobites from the Nuratau and Turkestan ranges, Uzbekistan and Tajikistan

Silurian trilobites of Ludlow and P?ídolí age are described from sections in southern Uzbekistan and from adjacent parts of Tajikistan. They belong to 22 species (10 named and 12 under open nomenclature) distributed among 13 genera belonging to the families Proetidae, Tropidocoryphidae, Aulacopleuridae, Scharyiidae, Cheiruridae, Encrinuridae and Odontopleuridae. The following new species are described: Interproetus pentaxus, Paleodechenella turkestanica, P. zaaminicus, Cromus tamchii and Leonaspis nuratensis. The generic associations from the mid Ludlow bear a striking resemblance to coeval ones from Bohemia, and include genera otherwise known only from that region or from adjacent parts of central Europe. The trilobite faunas from the late Ludlow and P?ídolí series are much less diverse and are dominated by genera of the Warburgellinae (Tropidocoryphidae), which include one species common to Vaigatch Island in the Russian Arctic, and Podolia, Ukraine. The closest links of the diverse central Asian mid Ludlow faunas are therefore to central Europe, whilst the sparser younger Ludlow and P?ídolí faunas, such as they are, suggest closer links to Baltica.     

Fungal endorhizal associates of Equisetum species from Western and Arctic Canada

We describe endorhizal fungi associated with Equisetum species collected from Ellesmere Island (82°N), Axel Heiberg Island (80°N), and from sites in Yukon Territory and the Prairie Provinces (51–67°N). Fungal colonization was assessed using a multiple quantitation microintersect method for lactofuchsin-stained roots examined with wide-field and confocal epifluorescence microscopy. Equisetum roots host abundant and diverse endorhizal fungal associates. For 85 specimens from 14 sites, total colonization averaged 30 ± 3%, range 0–97%. Colonization rates for wide aseptate hyphae characteristic of arbuscular mycorrhizae (5 ± 1%) was significantly less than for fine endophytes (20 ± 3%) or septate endophytes (17 ± 2%). Equisetum spp. are abundant in tundra and an important understory plant in boreal forests, where they are particularly common on burned or disturbed sites. Endorhizal fungi associated with Equisetum may have broad ecological relevance.     

Biogeographical analysis of Late Silurian brachiopod faunas, chiefly from Asia and Australia

Shallow water benthic marine invertebrates (such as brachiopods from Benthic Assemblages [BA] 1–3) have usually played a much more important role than deeper ones (BA 4–5 or even deeper) in evaluating biogeographical provincialism in geological history. The Silurian brachiopod Retziella Fauna, characterized by the common presence of Retziella in association with various provincial taxa and many common North Silurian Realm genera, is known from southwest Tienshan, North China, South China, North Vietnam, and East Australia. It is possibly also present in North Korea, the central Pamirs, Afghanistan, and New Zealand. The coeval Tuvaella Fauna occurs only in the southern marginal belt of the Siberian Plate. Synecologically, both faunas inhabited a normal, shallow-water, level-bottom environment, usually with a low-diversity community (commonly 3–8 genera); assignment to BA 2–3 is indicated. Their mutual exclusiveness is of biogeographical significance: subdivisions of the Uralian-Cordilleran Region can be based on them, with the Tuvaella Fauna being included in a redefined Mongolo-Okhotsk Province. A Sino-Australian Province is established and defined herein for the area occupied by the Retziella Fauna during the Ludlow-Pridoli and probably the Wenlock. Two subdivisions of the province can be recognized, a Sino-Central-Asian Subprovince and an Australian Subprovince, based on different endemic brachiopods and separate geographical positions. The presence of a number of more cosmopolitan genera in both the tropical-subtropical Sino-Australian and subtropical-temperate Mongolo-Okhotsk Provinces during the Late Silurian testifies to oceanic surface current circulation patterns adequate for the distribution of planktic larvae capable of long-distance dispersal while maintaining reproductive communication. This contrasts with the dispersal potential of endemic components of the newly defined Silurian biogeographical units. □ Late Silurian, Brachiopoda, Retziella , Fauna, Tuvaella Fauna, Synecology, Biogeography, Asia, Australia     

Arctic shrub colonization lagged peak postglacial warmth: Molecular evidence in lake sediment from Arctic Canada

Arctic shrubification is an observable consequence of climate change, already resulting in ecological shifts and global‐scale climate feedbacks including changes in land surface albedo and enhanced evapotranspiration. However, the rate at which shrubs can colonize previously glaciated terrain in a warming world is largely unknown. Reconstructions of past vegetation dynamics in conjunction with climate records can provide critical insights into shrubification rates and controls on plant migration, but paleoenvironmental reconstructions based on pollen may be biased by the influx of exotic pollen to tundra settings. Here, we reconstruct past plant communities using sedimentary ancient DNA (sedaDNA), which has a more local source area than pollen. We additionally reconstruct past temperature variability using bacterial cell membrane lipids (branched glycerol dialkyl glycerol tetraethers) and an aquatic productivity indicator (biogenic silica) to evaluate the relative timing of postglacial ecological and climate changes at a lake on southern Baffin Island, Arctic Canada. The sedaDNA record tightly constrains the colonization of dwarf birch (Betula, a thermophilous shrub) to 5.9 ± 0.1 ka, ~3 ka after local deglaciation as determined by cosmogenic ¹⁰Be moraine dating and >2 ka later than Betula pollen is recorded in nearby lake sediment. We then assess the paleovegetation history within the context of summer temperature and find that paleotemperatures were highest prior to 6.3 ka, followed by cooling in the centuries preceding Betula establishment. Together, these molecular proxies reveal that Betula colonization lagged peak summer temperatures, suggesting that inefficient dispersal, rather than climate, may have limited Arctic shrub migration in this region. In addition, these data suggest that pollen‐based climate reconstructions from high latitudes, which rely heavily on the presence and abundance of pollen from thermophilous taxa like Betula, can be compromised by both exotic pollen fluxes and vegetation migration lags.