The appearance of Baragwanathia (Lycophytina) in the Silurian

The evidence mainly involving graptolites is restated which supports an Upper Silurian (Ludlow) dating for a vascular flora containing Baragwanathia (Lycophytina) in Victoria, Australia.     

The apparatus of panderodontid conodonts

A cluster of thirteen elements of Panderodus unicosfatus (Branson & Mehl) from the Llandoverian of Po-dolia, Ukraine, is shown to represent an almost complete apparatus; only one element is lacking. The restored original arrangement of the elements is consistent with the model of the conodont apparatus with seven pairs of elements ordered in two parallel rows, with cusps opposing in every pair. The apparatus of Panderodus is closely similar to that of the Cambrian 'protoconcdonts' and their Recent chaetognath successors. Nevertheless, general trends in the evolution of elements of the Panderodontidae towards increased elongation, smoothness of the cusp curvature, and depth of the basal cavity indicate that the grasping apparatus of Panderodus developed independently of, and convergently to, that of the Chaetog-natha.     

Mode of life of the Silurian uncoiled gastropod Semitubina sakoi n. sp. from Japan

Semitubina sakoi n. sp. from the late Silurian of Japan represents the second species of this genus and also the first record of a Silurian gastropod in Japan. The gastropod shells occur in a thin mudstone bed and were found to be encrusted exclusively by corallites of ? Favosites sp. These corallites reveal that encrustation proceeded as the gastropod shells grew. The ecological relationship between the two organisms is considered to be symbiotic. This mode of life allowed the coral to live on a muddy substrate because clear sea water passed over the colony as the gastropod moved along. The gastropod benefited from this relationship by being protected from shell-boring or shell-crushing predators by the encrusting corallite. In Semitubina sakoi the body whorl is separated from the penultimate one by a considerable gap in a later growth stage and S. sakoi has been cited as one of the uncoiled gastropods. The uncoiling of this gastropod results primarily from rapidly increasing whorl translation rate in the latest growth stage. Taking the symbiotic relationship with ? Favosites sp. into consideration, a deposit feeding or benthic scavenging mode of life is suggested for this gastropod.     

Ostracode fauna, stratigraphy and definition of the Beyrichienkalk sequence

An essential clue to the uppermost Silurian in the submarine Baltic arca is the Beyrichienkalk. According to recent investigations it constitutes a glacial drift boulder sequence characterized by four ostracode associations with about sixty species. In the correlation of ostracode zones of Baltoscandia these associations form a connecting link and thus are also of biozonal character. In the terms of regional stratigraphic units (East Baltic arca). the lower stratigraphic boundary of this sequence lies approximately at the beginning of the Kuressaare beds and the top in the upper Ohesaare beds. The term Beyrichienkalk should be used for those glacial erratics that are characterized by typical ostracodes of the four associations defined here.     

The ichnogenus Tremichnus in the Lower Silurian of western New York

Discovery of Tremichnus cysticus Brett on a crinoid pluricolumnal from the Willowvale Shale of western New York extends the range of this ichnogenus into the Lower Silurian. Pits attributable to Tremichnus apparently represent embedment sites of parasites or commensalistic, filter-feeding organisms of unknown affinities. Embedment of T. cysticus may have been accomplished by localized inhibition of stereom growth within the pits aided by secretion of substances that stimulated accretion of stereom by the host pelmatozoan in areas immediately surrounding the pits.     

A new mid-Silurian aquatic scorpion—one step closer to land?

One of the oldest known fossil scorpions, a new species from the mid-Silurian Eramosa Formation (430 myr) of Ontario, Canada, exhibits several surprising features. The depositional environment and associated biota indicate a marine habitat; however, the leg morphology of this scorpion, which has a short tarsus in common with all Recent scorpions, suggests that a key adaptation for terrestrial locomotion, the ability to support its weight on a subterminal ‘foot’, appeared remarkably early in the scorpion fossil record. Specimens are preserved intact and undisturbed in a splayed posture typical of moults rather than carcasses. We postulate that these animals were aquatic, but occasionally ventured into extremely shallow water, or onto a transient subaerially exposed surface while moulting, before returning to deeper water. Shed exuviae were preserved in situ by rapid overgrowth of bacterial biofilm.     

云南曲靖志留纪罗德洛世真盔甲鱼类一新属(英文)

记述了云南曲靖潇湘区关底组(志留系罗德洛统)真盔甲鱼类一新属、新种——长孔盾鱼(Dunyu longiforus gen.et sp.nov.),丰富了以梦幻鬼鱼为代表的潇湘脊椎动物群的组成。该新属具真盔甲鱼科的鉴别特征:后眶上管和中背管二者连续过渡,后端两侧辏合呈"U"字形,侧背管仅发出3条侧横管。新属内角缺如,这一特征过去在真盔甲鱼科中仅见于真盔甲鱼属。新属区别于真盔甲鱼属的主要特征有:角向后方延伸,呈棘状或叶状;头甲最宽处位于角末端之前,宽长比小于1.1;中背孔末端超越眶孔后缘连线。基于对秀山真盔甲鱼头甲标本的重新观察,将秀山真盔甲鱼归入盾鱼属。新种区别于秀山盾鱼(Dunyu xiushanensis)的特征有:个体较大,头甲长大于宽;角呈棘状;眶孔位置相对靠前,头甲眶前区与眶后区的长度之比小于0.75;多边形崮状瘤点,较大,长可超过2mm。     

Carbon isotopes support the presence of extensive land floras pre-dating the origin of vascular plants

Multiple lines of evidence indicate that Earth's land masses became green some 2.7 Ga ago, about 1 billion years after the advent of life. About 2.2 billion years later, land plants abruptly appear in the fossil record and diversify marking the onset of ecologically complex terrestrial communities that persist to the present day. Given this long history of land colonization, surprisingly few studies report direct fossil evidence of emergent vegetation prior to the continuous record of life on land that starts in the mid-Silurian (ca. 420–425 Ma ago). Here we compare stable carbon isotope signatures of fossils from seven Ordovician–Silurian (450–420 Ma old) Appalachian biotas with signatures of coeval marine organic matter and with stable carbon isotope values predicted for Ordovician and Silurian liverworts (BRYOCARB model). The comparisons support a terrestrial origin for fossils in six of the biotas analyzed, and indicate that some of the fossils represent bryophyte-grade plants. Our results demonstrate that extensive land floras pre-dated the advent of vascular plants by at least 25 Ma. The Appalachian fossils represent the oldest direct evidence of widespread colonization of continents. These findings provide a new search image for macrofossil assemblages that contain the earliest stages of land plant evolution. We anticipate they will fuel renewed efforts to search for direct fossil evidence to track the origin of land plants and eukaryotic life on continents further back in geologic time.     

中国奥陶纪晚期—志留纪早期孢型植物及古地理意义

中国奥陶纪晚期的孢型植物组合以隐孢子为主,不含真正三缝孢,称为Tetrahedraletes medinensis-Dy-adospora murusattenuata-Laevolancis chibrikovae(MMC)组合;中国志留纪早期孢型植物组合以隐孢子为主,包括四分体和单分体,缺失二分体,出现真正三缝孢,并产生不同的类型(光面、具纹饰、具弓形脊等类型),被称为Tet-rahedraletes medinensis-Laevolancis chibrikovae-Ambitisporites avitus/dilutus(MCA)组合。孢型植物化石的某些相似性表明:华南和塔里木板块可能分布于相近的低古纬度,气候特征具有一定的可比性,代表近赤道的热带气候;至少在志留纪早期,华南和印支板块与冈瓦纳大陆距离较近,可能处于同一古气候带,代表相似的生物古地理特征。     

Taphonomy and affinity of an enigmatic Silurian vertebrate,Jamoytius kerwoodi White

Abstract: The anatomy and affinities of Jamoytius kerwoodi White have long been controversial, because its complex taphonomy makes unequivocal interpretation impossible with the methodology used in previous studies. Topological analysis, model reconstruction and elemental analysis, followed by anatomical interpretation, allow features to be identified more rigorously and support the hypothesis that Jamoytius is a jawless vertebrate. The preserved features of Jamoytius include W‐shaped phosphatic scales, 10 or more pairs of branchial openings, optic capsules, a circular, subterminal mouth and a single terminal nasal opening. Interpretations of paired ‘appendages’ remain equivocal. Phylogenetic analysis places Jamoytius and Euphanerops together (Jamoytiiformes), as stem‐gnathostomes rather than lamprey related or sister taxon to Anaspida.