Anatomical reinvestigation of Archaeopteris macilenta from the Upper Devonian (Frasnian) of South China

Abstract Archaeopteris macilenta is one of the most widespread plants in the Late Devonian. Based on fossils from the Frasnian Huangjiadeng Formation, Yichang District of Hubei Province, for the first time we study in detail the anatomy of this progymnosperm plant in South China. Ultimate axes are protostelic with three xylem sympodia and lack secondary tissue. Penultimate axes are eustelic, bearing eight sympodia and a thin band of secondary xylem. Radially symmetrical sympodia of mesarch primary xylem produce traces of appendages in a spiral arrangement. Archaeopteris macilenta and A. halliana (A. roemeriana) are dominant in the Frasnian and Famennian, respectively. Comparisons with these two species from other tectonic plates indicate consistent stelar architectures. Global spread, continuous occurrence, and identical anatomy during the Late Devonian indicate that Archaeopteris survived the Frasnian–Famennian extinction event. In this time, endemic genera and cosmopolitan taxa, including Archaeopteris, suggest the palaeogeographic isolation of South China and certain associations with other plates.     

An anatomically preserved arborescent lycopsid, Sublepidodendron songziense (Sublepidodendraceae), from the Late Devonian of Hubei, China

Sublepidodendron is a common megafossil plant in the Late Devonian of China, but historically the generic delimitation based on leaf bases masked its true systematic position. A reinvestigation of S. songziense from the Late Devonian Hsiehchingssu Formation, Hubei, China, provides new insights into its internal anatomy and reproductive morphology. This arborescent lycopsid is characterized by small, vertically elongated leaf bases arranged in spirals, presence of false leaf scars, possibly bearing separate cones, and association with a stigmarian rhizomorph. The potential for organic connections of these detached organ genera has been noted for other Sublepidodendron species. The anatomy of S. songziense axes from two levels reveals that the thinner axis may bear an ectophloic siphonostele with a filamentous pith and an outer cortex. The thicker axis has a siphonostele with a branch gap, two-zoned pith with secondary thickenings, multiseriate rays across secondary xylem, a thick periderm, and primary and secondary tracheid walls characterized by "Williamson's striations." Similarities to synapomorphies of Diaphorodendraceae and Lepidodendraceae suggest that S. songziense bears a closer affinity to Lepidodendrales rather than Protolepidodendrales, as formerly thought. Widespread occurrence of Sublepidodendron implies that phylogenetically advanced arborescent lycopsids must have diverged by the Late Devonian.     

Late Devonian global ostracod palaeobiogeography

A global Late Devonian ostracod database is constructed, incorporating new materials from South China and Northwest China. Four palaeobiogeographical units (Cathaysia, North America, Europe and peri‐Gondwana) are recognized during the Frasnian and five palaeobiogeographical units (Cathaysia, North America, Europe, Siberia and Australia) in the Famennian. Three controlling factors (climatic zonation, geographical isolation and global sea‐level changes) are identified to have played roles in shaping the palaeogeographical regionalization of ostracod faunas in the Late Devonian. The ostracod palaeobiogeography in the Frasnian was mainly influenced by climatic zonation, while rapid changes in tectonic configuration in the Famennian drastically altered the global palaeobiogeography of ostracods. The palaeobiogeographical regionalization of ostracod faunas suggests that Laurussia and Gondwana continued to draw near during the Late Devonian, with the first collision occurring in Southern Central Europe in the Famennian. The South China plate drifted northward to the Kazakhstan plate away from the Australian plate, which gradually became isolated during the Famennian Stage.     

华南泥盆系法门阶浅海相四射珊瑚的组合序列

晚泥盆世弗拉期末F-F的生物灭绝事件,导致珊瑚以及许多浅海底栖生物灭绝,几乎整个法门期珊瑚群都处于残存阶段,华南地区目前只在湖南的个别地方发现少量的Smithiphyllum。直到法门期末珊瑚和其它一些造礁底栖生物开始复苏,出现了不少与典型泥盆纪珊瑚存在很大差别的新分子。华南泥盆纪最晚期(Strunian)的珊瑚可划分成上、下两个组合:上部Cystophrentis组合;下部Eocaninophyllum组合。泥盆—石炭纪之交的另一次生物灭绝事件,使新生的泥盆纪最晚期的珊瑚又遭灭绝。     

ACTINOXYLON BANKSII GEN. ET SP. NOV.: A PROGYMNOSPERM FROM THE MIDDLE DEVONIAN OF NEW YORK

A new genus from a Middle Devonian locality near Cairo, N. Y., is described. Actinoxylon gen. nov. is based upon pyritic petrifactions. Three orders of branching are present: penultimate branch, ultimate branch, and leaf. The penultimate branch bears spirally arranged ultimate branches and leaves, the leaves apparently replacing the branches in the spiral. The ultimate branches bear opposite to subopposite and decussate leaves. The leaves are non-planated, unwebbed structures which show at least three dichotomies. Each segment of the leaf is terete as are all other axes. Internally the penultimate branch has a six-lobed actinostele with mesarch protoxylem areas, one or two per lobe. Secondary xylem is visible in the oldest parts of several specimens. The xylem has helical-reticulate, reticulate, scalariform and circular-pitted elements. The presumptive areas of phloem are occupied by cells with dark contents. The cortex is composed of a parenchymatous inner region and a sclerenchymatous outer region. The ultimate branch traces are at first three-lobed protosteles, later becoming four-lobed. Several ultimate branch traces also possess secondary xylem while within the cortex of the penultimate branch. The leaf traces are terete strands. Below each forking of a leaf segment there is a corresponding forking of the vascular strand. Actinoxylon is compared with the progymnosperms Actinopodium, Svalbardia, Archaeopteris, Siderella, and Tetraxylopteris. The anatomy of the penultimate branch of Actinoxylon is similar to that of Actinopodium, Archaeopteris macilenta, and Siderella. The ultimate branch traces of Archaeopteris and Actinoxylon are similar. The ultimate branch stele and pattern of trace formation in Actinoxylon is similar to the stelar configuration and trace formation in the r + 2 axes of Tetraxylopteris schmidtii. The unwebbed leaves are similar to those of Archaeopteris fissilis, Svalbardia, and the terminal units of the Aneurophytales.     

An anatomically preserved lycopsid from the Upper Devonian of South China

An anatomically preserved lycopsid, Lobodendron fanwanensegen. et sp. nov. Liu, Wang, Xue & Meng, is described from the Upper Devonian (Famennian) Wutong Formation of Changxing County, Zhejiang Province, China. The fossil plant bears slender, dichotomously branched axes. The vascular strand consists of solid terete primary xylem and lobed secondary xylem, which implies the result from the activity of possibly discontinuous cambium. The new plant has character combinations that do not conform to any branches in the canopy of the tree-lycopsids known previously, but resemble those of the basal part of some pseudoherbaceous lycopsids. This new plant may exemplify a Late Devonian lycopsid with a pseudoherbaceous growth habit.     

Frasnian (Upper Devonian) evidence for multiple origins of seed-like structures

Reproductive structures of Frasnian (early Late Devonian) age from Wuhan, Hubei province, South China provide evidence for the early emergence of monomegaspory and integumentation in plants of non-progymnosperm affinity. Sphinxia wuhania gen. et sp. nov. pre-dates the occurrence of other reproductive structures exhibiting a similar suite of characters and adds support to the view that evolution towards an ovule may not have been a unique event. Sphinxia possesses a single functional megaspore with associated aborted members of the meiotic tetrad, a distinct, striated sporangial wall, and a sterile envelope bearing proximal spines. The morphology of the structure precludes assignment to any known group of plants in the absence of additional information regarding the parent plant. A progymnospermous affinity is unlikely. Thus, Sphinxia demonstrates that the Devonian progymnosperms did not lack potential competition from similarly specialized reproductive strategies in other plant lineages.     

贵州南部独山地区泥盆纪弗拉期的石燕贝类腕足动物

弗拉期是了解泥盆纪弗拉-法门灭绝事件之前古代生物多样性的一个关键阶段.贵州南部的独山地区因其所具有的完整层序及丰富的底栖牛物化石成为我国主要泥盆系参考剖面之一.独山剖面弗拉期的石燕贝类腕足动物至少包括5种类型,其中4种在本文中为首次描述和图示.Conispirifer之前只发现于欧洲及北美的弗拉期地层中,目前也首次在华南独山剖面的同期地层中发现.大多先前从贵州南部其他地区弗拉期地层中描述的多种Cyrtospirifer可归于Cyrtospirifer subextensoides新种内.鉴于前人对Emanuella的模式种E.takwanensis 的内部构造描述的矛盾状况,本文暂把研究区具有抬离壳面的纤细铰窝、固着于壳面的主突起以及其前方下面为外铰板支撑的标本归于E.takwanensis.在华南弗拉期可初步识别出三个腕足动物群组合带:Yocrarhynchus-Phlogoiderhynchus动物群以小嘴贝类-无洞贝类-双腔贝类腕足动物为特征,其时代大致从弗拉阶底部至Pa.punctata带;之后为Cyrtospirifer动物群,以Cyrtospirifer的存在为特征,又可分为早晚两部分,前者(未命名)以conispiriferid类的Conispirifer和Pyramidaspirifer、弓石燕类、无洞贝类等为特征,其时代大致为Pa."hassi"带至下Pa.rhenana带;后者为Hunanotoechia动物群,以丰富的小嘴贝类-无洞贝类.弓石燕类腕足动物为特征,其时代大致为上Pa.rhenana带至Pa.1inguiformis带.     

Sphenophyllum Brongniart (Sphenopsida) from the Upper Devonian of South China

Sphenophyllum Brongniart constitutes a common and important element in the Carboniferous and Permian floras around the world, but its records in the Devonian Period are limited and remain to be investigated with respect to their morphology, anatomy, and distribution. Diversity of Sphenophyllum during Late Devonian in South China was significant with the presence of the well-known species including S. lungtanense Gothan and Sze, S. pseudotenerrimum Sze, and S. changxingense Huang et al. In this article, we describe a new species of the genus, S. fanwanense n. sp., from the Fanwan section of Changxing County, Zhejiang Province, characterized by having at least two orders of axes, with six spoon-shaped leaves attached at the node. A comprehensive review of previous records of Sphenophyllum from the Upper Devonian of South China shows that at least four species (S. fanwanense, S. lungtanense, S. pseudotenerrimum and S. changxingense), each with distinct leaf morphology, occur in South China in the Late Devonian, mostly from the Wutong Formation (Famennian). Given the lack of concrete evidence for anisophylly or heterophylly among the Devonian Sphenophyllum species (and more broadly, the Devonian sphenopsids), we suggest that the development of these features later in the Carboniferous and Permian periods was likely related to an increase in complexity of forest communities through time.     

New perspective on the architecture of the Late Devonian arborescent lycopsid Leptophloeum rhombicum (Leptophloeaceae)

A reinvestigation of the previously described Leptophloeum rhombicum trunk from the Late Devonian (Frasnian) Huangchiateng Formation of Hubei, China provides a new perspective on the architecture of this arborescent lycopsid. It is preserved as a flattened, silicified petrification with an unevenly permineralized primary vasculature and spirally arranged rhombic leaf cushions, which agree with the diagnosis of L. rhombicum Dawson distributed worldwide in the Late Devonian. Taxonomically, this plant should be assigned to its own family and within the order Iso?tales sensu lato. The anatomy, from different levels of the trunk, demonstrates that the ontogeny of the plant may conform to a determinate growth pattern. Combining previous data with current architectural analysis, it suggested that the L. rhombicum tree had a pseudomonopodial branching pattern rather than an iso-dichotomous branching crown as previously proposed. New reconstruction of the general habit for this tree is given and consists of three major architectural units: a stigmarian rhizomorph, a main trunk, and lateral branches. When these results are considered with recent cladistic work, L. rhombicum may have developed similar growth architecture to some Famennian and Carboniferous arborescent lycopsids. This growth represents one of the archetypal architectures found in the Iso?tales s.l. extending from the early Late Devonian.     

Evidence of polar auxin flow in 375 million-year-old fossil wood

In living woody seed plants (conifers and dicotyledons), when various obstacles such as buds and branches disrupt the axial polar auxin flow, auxin whirlpools are formed that induce the differentiation of circular tracheary elements in the secondary xylem. Identical circular patterns also occur at the same positions in the wood of the 375 million-year-old Upper Devonian fossil progymnosperm Archaeopteris. We propose that this is the earliest clear fossil evidence of polar auxin flow. Such spiral patterns do not occur in the primary xylem of the ca. 390-385 million-year-old Lower Devonian fossil land plants, fossil progymnosperms, Psilotum nudum, living ferns, and current seed plants that we examined. This discovery reveals an exciting potential for plant fossils to provide structural evidence of evolutionarily diagnostic physiological and developmental mechanisms and for the use of a combination of fossil evidence and developmental biology to characterize evolutionary patterns in terms of genetic changes in growth regulation.     

Gymnosperm trees from the Permian of Antarctica: An anatomically preserved trunk of Kaokoxylon sp.

Anatomically preserved gymnosperm axes are relatively abundant in Permian localities of Antarctica, but their anatomy has rarely been studied in detail, which limits comparison with other Gondwanan morphotaxa. Here we describe a silicified trunk collected from the Upper Permian Buckley Formation at Coalsack Bluff, in the central Transantarctic Mountains. The trunk has a small heterogeneous pith approximately 4 mm in diameter containing conspicuous sclerotic nests, endarch primary xylem maturation, paired leaf traces, and secondary xylem of the Araucarioxylon type. Comparison with contemporaneous gymnosperm axes from Antarctica indicates that the Coalsack Bluff trunk represents a new Permian morphotaxon for the region. The anatomical characters of the pith and secondary xylem suggest an affinity with the genus Kaokoxylon Kräusel, previously reported from Permian and Triassic localities of Southern Africa, South America, India, and Australia.     

Palynostratigraphy and palaeogeography of the Padeha, Khoshyeilagh, and Mobarak formations in the eastern Alborz Range (Kopet-Dagh region), northeastern Iran

A total of 113 surface samples collected from the Padeha, Khoshyeilagh, and Mobarak formations of Kuh-e-Ozum, northeast of Jajarm town were processed for palynomorphs, in order to determine age relationships. Well-preserved and abundant palynomorphs dominated by organic-walled-marine microphytoplankton (acritarchs and prasinophyte phycomata), miospores and subordinate chitinozoans, and scolecodonts were recovered. Seven species of prasinophyte phycomata (four genera), 19 acritarch species (14 genera), one species of chitinozoa, and 26 miospore species (19 genera) were recorded and assigned to eight local Assemblage Zones. Assemblage Zones I-IV occur in the Padeha Formation and suggest an Early Late Devonian (Frasnian) age whilst assemblages zones V-VII are present in the Khoshyeilagh Formation and indicate Late Devonian (Famennian) ages. Assemblage zone VIII, which occurs in the basal part of Mobarak Formation, suggests a Lower Mississippian (Tournaisian) age for this formation. Many of the palynomorph groups encountered are closely comparable with coeval assemblages recorded from Western Australia, southwest Ireland, England, Turkey, Saudi Arabia, North Africa, and South America, indicating the close relationship of the Iranian Platform to other parts of the northern Gondwana Domain during the time interval represented by these strata. The presence of marine palynomorphs (acritarchs/prasinophyte phycomata, chitinozoans, and scolecodonts), and shelly macrofauna (brachiopods, gastropods, and corals) in Member c of the Padeha Formation (as well as the Khoshyeilagh and Mobarak formations), together with associated miospores, indicate an open marine (moderately nearshore) depositional environment for the Upper Devonian and Lower Carboniferous deposits in northeastern Alborz Range (Kopet-Dagh region) of Iran.     

The development of Archaeopteris: new evolutionary characters from the structural analysis of an Early Famennian trunk from southeast Morocco

A 5 m long trunk of a young Archaeopteris/Callixylon erianum tree from the Late Devonian of Morocco shows new branching patterns for early lignophytes. This progymnosperm tree produces a helical pattern of traces that we infer belonged to reduced, short-lived, primary (apical) branches (type A) as well as two types of adventitious traces (types B and H). We infer that type-B traces supplied branches that initiate close to the site of attachment on the trunk of some, but not all type-A branches in an irregular but nonrandom pattern. Unlike ephemeral type-A branches, those of type B persist and become long-lived, potentially permanent units of the architecture of Archaeopteris trees. Type-H adventitious traces are also short-lived and occur singly or in serial groups, but differ from traces of either type A or B branches by lacking differentiation into a readily identifiable organ category. We interpret type-H traces as supplying latent primordia that could develop into either adventitious roots or shoots depending on extrinsic factors. Our new data suggest that Archaeopteris had a wide range of branch primordium amplitude. Type-B branches compare with axillary lateral branch buds of some Early Carboniferous spermatophytes (Calamopitys) and are a major developmental departure from the strictly apical, pseudomonopodial shoot branching of older aneurophyte progymnosperms. Type-H traces suggest that Archaeopteris trees had some potential for formation of adventitious roots or shoots in response to environmental factors, such as partial burial by overbank sedimentation. Collectively, these novel methods of tree branching may partly explain the extraordinary success and worldwide dominance of Archaeopteris forests on fluvially dominated, Late Devonian floodplains.     

RELLIMIA THOMSONII FROM THE GIVETIAN OF NEW YORK: SECONDARY GROWTH IN THREE ORDERS OF BRANCHING

Pyritized axes of the vegetative branching system of Rellimia thomsonii, from the Givetian of New York were described with emphasis on the presence and position of the secondary tissues in relation to the known axis orders. The morphology and anatomy of four axis orders (N, N + 1, N + 2, N + 3) was described using two well-preserved specimens. One specimen showed the largest known (N) axis order, with spirally attached N + 1 axes. The other specimen, from a more distal portion of the plant, showed the N + 2 axis order with spirally arranged N + 3 axes. The shape of the primary xylem, discernible in three of the axis orders (N + 1, N + 2, N + 3), was a three-lobed protostele with mesarch maturation of the primary xylem. The protostele of the N + 3 axis order, with only primary growth, was identical to that of fertile N + 3 axes. The other axis orders (N + 2, N + 1, N) had wood surrounding the primary xylem. The wood of the N+2 axis was limited, and occurred only in the basal portion of the axis, but that of the N+1 and N axes was extensively developed with two and three growth layers, respectively. This wood was pycnoxylic with narrow rays similar to other aneurophytalean progymnosperms. Surrounding the secondary xylem was secondary phloem indicating the vascular cambium in Rellimia was bifacial. The presence of growth layers was discussed in relation to the climatic interpretation placed on their presence and how it correlates with paleogeographic reconstructions of the Devonian.     

Devonian Vertebrates From Colombia

Vertebrate remains are reported from the Emsian–Eifelian Floresta Formation and the Late Devonian (?Frasnian) Cuche Formation of north‐eastern Colombia. The material from the Floresta Formation is associated with a marine invertebrate fauna and includes an arthrodire and probably a rhenanid. Several vertebrate‐bearing localities are recorded from the Cuche Formation; vertebrates occur with plant remains and lingulid fragments. They include an acanthodian (Cheiracanthoides? sp.), a chondrichthyan (Antarctilamna? sp.), placoderms (Bothriolepis sp., Asterolepis? sp. and an undetermined groenlandaspidid or primitive brachythoracid arthrodire), a stegotrachelid actinopterygianand three sarcopterygians (a cosmine‐covered form tentatively referred to an osteolepidid, the porolepiform Holoptychiussp., and the rhizodontid Strepsodus? sp.). This assemblage suggests a Late Frasnian age and is surprisingly similar to Late Devonian vertebrate assemblages found in similar facies of Europe and North America, notwithstanding the presence of the Gondwanan chondrichthyan Antarctilamna?. key words: Vertebrata, Devonian, Colombia, South America, biostratigraphy, palaeobiogeography.     

Re-study of Minostrobus chaohuensis Wang (Lycopsida) from the Upper Devonian of Anhui,South China

Minostrobus chaohuensis Wang was previously known only as a lycopsid megasporangiate strobilus from the Upper Devonian of Anhui Province, South China. Our comprehensive study of the newly collected materials reveals the details of its morphology, anatomy, and reproduction, which allow us to emend its generic and specific diagnoses. M. chaohuensis is reconstructed as a plant with multi-dichotomous branching system, helically arranged leaves, and monoecious and monosporangiate strobili (i.e., separate megasporangiate and microsporangiate strobili in one individual). The anatomy of both fertile and sterile portions of Minostrobus indicates that the exarch primary xylem strand is the solid protostele, with the peripheral protoxylem ridges and Williamson's striations in metaxylem tracheids. The key reproductive and anatomical characters suggest that Minostrobus chaohuensis is far more likely to represent a distal shoot of pseudo-herbaceous or arborescent lycopsids within the order Isoëtales sensu lato. It is suggested that the monosporangiate-strobilus clade in the Isoëtales may include primitive, monoecious taxa in the Late Devonian and advanced, dioecious ones in the Carboniferous. The hypothesis that the more phylogenetically advanced monosporangiate-strobilus clade might have well diverged from the basal bisporangiate-strobilus clade of arborescent lycopsids by the Late Devonian is further supported.     

桂东、桂东南晚泥盆世一个弗拉斯期放射虫动物群

本文系统描述了广西玉林、贺县等地晚泥盆世榴江组硅质岩中的放射虫化石4属14种,其中有1新属2新种。这个放射虫动物群的多数分子曾见于苏联南乌拉尔地区和澳大利亚的弗拉斯阶。     

New radiolarians from the Devonian of the southern Ural Mountains: 2. Middle-Late Devonian

Middle-Late Devonian Radiolarians are recorded for the first time in the southern Ural Mountains in Bashkortostan, in a section of Kariukmas Mountain (Upper Eifelian) and on the southern slope of Argagan Mountain (Middle Frasnian). The new Late Eifelian assemblage is composed of 17 species of 11 genera, and Middle Frasnian radiolarians comprise 13 species of 7 genera of spherical, discoidal, pylomate, and spiny radiolarians. A new species, Primaritripus kariukmasensis, sp. nov., is described. The prevalence of discoidal forms in the oryctocenosis suggests shallow marine conditions in the Late Eifelian and Middle Frasnian basins. Two new biostratons, the Upper Eifelian beds with Primaritripus kariukmasensis and Middle Frasnian beds with Primaritripus chuvashovi, are established based on radiolarians.     

Permineralized Callixylon woods from the Late Devonian Cleveland Shale of Ohio, U.S.A. and that of Kettle Point, Ontario, Canada

Two permineralized woods are described in this paper, one from the Late Devonian Cleveland Shale of Ohio, USA and the other from the Late Devonian Huron Shale of Kettle Point, Ontario, Canada. Both samples of wood are satisfactorily preserved with primary and secondary xylem but without cortex and bark. Both are identified as Callixylon. They differ in specific characters from each other and from other described species. Hence two new species are designated, Callixylon beckii and Callixylon huronensis, respectively, to accommodate them in the class Progymnospermopsida (Progymnospermophyta) under the group Archaeopteridales.