系统古生物研究中的统计新方法初探——以浙赣边区志留纪初期雕正形贝属为例

对浙赣交界地区志留系兰多维列统底部编号为DK4(浙江省淳安县大坑坞剖面安吉组)与AFL68(江西省玉山县上坞剖面仕阳组)的两批腕足动物化石中的雕正形贝(Glyptorthis)进行度量与描述,并研究其腹壳肌痕面在个体发育过程中的变化,最终将其确定为Glyptorthis wenchangensis(Liang)。在测量方法上,将"协方差分析"(covariance analysis)运用于这两个居群间的性状对比,效果较好。此外,针对系统古生物研究中的传统统计方法——"最小二乘回归"(least squares regression)潜在的问题与不足,作者引入并证明"鲁棒回归"(robust regres-sion)方法的优势所在。     

陕西宁强早志留世灰泥丘中微生物及其造岩意义

通过扫描电镜分析 ,在陕西宁强早志留世深缓坡微晶灰泥丘中发现 3种微生物化石 ,分别为 :( 1 )表面光滑卵球体 ,其大小为 5μm× 3μm ,壳体表面光滑 ,长轴端具有圆形凹坑或凸起 ,可能为芽体及芽痕 ;此类化石能与真菌类菌孢对比 ;( 2 )表面粗糙的椭球体 ,其大小为 60 μm× 50 μm ,壳体表面粗糙 ,具蠕虫状断续条纹 ,并有方解石胶结物生长 ;( 3)网格状结构 ,由钙化的胶质席状物及枝状物组成 ,网呈枝状分叉 ,盖覆于灰泥之上并参加造岩。经能谱分析 ,所有微生物化石均由碳酸钙组成 ,他们在灰泥丘的形成过程中起了重要的造岩作用     

CLASSIFICATION AND CONTROLS OF INTERNAL BANDING IN PALAEOZOIC STROMATOPOROIDS AND COLONIAL CORALS

Abstract:  Palaeozoic corals and stromatoporoids exhibit a variety of internal banding phenomena, many of which have been commonly interpreted as annual growth bands. We evaluate bands through analysis of colonial corals and stromatoporoids from three stratigraphic intervals: Upper Ordovician of Manitoba Canada, and Llandovery–Wenlock and Ludlow of Gotland, Sweden. Banding features are divided into four categories: (1) absence of banding; (2) density banding formed by variation in density or form of elements; (3) growth-interruption banding indicating growth cessation and regeneration; and (4) post-mortem banding caused by compaction or diagenesis. For discrimination of band types, it is essential to examine internal structures and skeletal margins in thin sections or acetate peels. Species vary considerably in degree and type of banding; each has a distinct pattern of variation. We propose criteria to determine if banding is consistent with seasonally induced growth variation: (1) consistency in band character and thickness; (2) continuity of skeletal growth; (3) marginal features; and (4) evidence of diagenetic alteration. Density bands in tabulate and rugose corals probably represent annual growth variations, but results for stromatoporoids are more ambiguous; although stromatoporoids commonly show banding, unequivocal density banding is poorly developed and growth interruption generated most stromatoporoid banding. Cerioid rugose and tabulate corals possess the thickest density bands; the thinnest bands are in stromatoporoids and heliolitid tabulates.     

A Silurian myodocope with preserved soft-parts: cautioning the interpretation of the shell-based ostracod record

Ostracod crustaceans are the most abundant fossil arthropods. The Silurian Pauline avibella gen. et sp. nov., from the Herefordshire Lagerstätte, UK, is an extremely rare Palaeozoic example with soft-part preservation. Based on its soft-part morphology, especially the exceptionally preserved limbs and presence of lateral eyes, it is assigned to the myodocopid myodocopes. The ostracod is very large, with an epipod on the fifth limb pair, as well as gills implying the presence of a heart and an integrated respiratory–circulatory system as in living cylindroleberidid myodocopids. Features of its shell morphology, however, recall halocyprid myodocopes and palaeocopes, encouraging caution in classifying ostracods based on the carapace alone and querying the interpretation of their shell-based fossil record, especially for the Palaeozoic, where some 500 genera are presently assigned to the Palaeocopida.     

The formation of micritic limestones and the development of limestone-marl alternations in the Silurian of Gotland,Sweden

Summary Micritic limestone-marl alternations make up the major part of the Silurian strata on Gotland (Sweden). Their position on the stable Baltic Shield protected them from deep burial and tectonic stress and allowed the preservation of early stages of burial diagenesis, including lithification. In the micritic limestones certain characteristics have been preserved (e.g., pitted microspar crystals, sharp boundaries between microspar and components, lack of deformation phenomena) that offer insights into their formation. We suppose the formation of these micritic limestones and limestone-marl alternations to be based on a rhythmic diagenesis within an aragonite solution zone (ASZ) close below the sediment surface. The micritic limestones are the product of a poikilotopic cementation of carbonate muds which consisted of varying portions of aragonitic, calcitic and terrigenous matter. Their microspar crystals show the primary size and shape of the cements lithifying the original carbonate mud. Dissolution of aragonite in the marls provided the carbonate for the lithification of the limestones. By cementation, the limestone beds evaded further compaction. The marls, which already underwent a volume decrease by aragonite depletion, lacked cement and became more and more compacted due to increasing sedimentary overburden. Although field observations show that primary differences in material influence the development of limestone-marl alternations they are not required for their formation.     

Enigmatic polychaete jaws from the Silurian of Gotland, Sweden

The jaws of the new polychaetaspid polychaete, Oenonites? honki, from the Silurian of Gotland, Sweden, differ from most Palaeozoic polychaete jaws. They exhibit enigmatic microstructural features in that they appear rough and give a corroded, or weathered impression. The altered microstructure of the jaws suggests a jaw chemistry and/or composition differing in some way from that of the co‐occurring polychaete taxa. The jaws appear to have limited preservational potential and/or were particularly susceptible to secondary processes, resulting in microstructural alteration. Commonly, a row of distinct pits occurs on the outer face, especially of the first right maxillae (MIr). Because these pits are interpreted as associated with the dentary, the term ‘denticle marks’ is suggested. The pits may be the result of primary or secondary physical wear, or, more probably, secondary chemical alteration of localized mineral deposits. The primary function of such mineral deposits was to harden those parts of the surface that were exposed to great stress. The restricted occurrence of O.? honki, coupled with occasional increases in abundance (especially in the Halla Formation, unit b), indicates a preference for shallow marine, high‐energy environments, particularly in reefal pockets with calcilutitic sediments. Highest frequency coincides with faunas characteristically containing a few labidognath species also displaying high frequencies.     

A southward extension of the Silurian Tuvaella brachiopod fauna

The co-occurrence of Tuvaella gigantea Chernyshev, Tannuspirifer pedaschenkoi (Chernyshev), Leptos-trophia elegestica Chernyshev and Stegerhynchus sp. in the Upper Hongliuxia Formation, Barkol, NE Xinjiang, China, shows that this is a representative of the well-known Tuvaella Fauna in China. The correlation of the Tuvaella gigantea Assemblage Zone of the Upper Hongliuxia Formation at its type locality is discussed to document the correlation of this formation with the Pichishui Beds of the Upper upper Chergak Formation in Tuva, the Woduhe Formation m the Lesser Khingan Mountains, and other equivalents based on the presence in some abundance of T. gigantea , and without T. rackovskii. The Tuvaella gigantea-bearing strata are tentatively assigned to the Ludlow. With regard to the paleozoogeographic affinity of the Tuvaella Fauna it is at present suspected by some that the area inhabited by Tuvaella represents a peculiar zoogeographic province or region during the Silurian. However, the information available indicates that the Tuvaella occurrences in east-central Asia represent nothing more than a specialized environmental situation in the light of the presence of a single endemic genus, i.e. Tuvaella itself, among 25 articulate brachiopod genera examined. The evidence of both lithology and brachiopods investigated has important implications for suggesting a shallow, commonly rough-water environment between low intertidal and high subtidal areas.     

New observations on the fine structure of graptoblasts

Graptoblasts are redefined as widenings of the sealed terminal portions of graptolite stolothecae resulting in ovoid bodies composed of an outer fusellar layer, named here as blastotheca, and an inner secondary layer of electron dense material, named the blastocrypt. In their proximal portion a number of graptoblasts display a scar with fuselli stripped and the crassal material of the blastotheca exposed and displaying a rough and dull surface. The boundary of this area, termed the talus, is edged by a distinct escarpment, probably the margin of the preserved part of the blastotheca. The outer wall of the talus is usually abruptly terminated. Only exceptionally is the outer wall conical and gradually widening. Thus the transverse partition between the parental stolotheca and the graptoblast was produced by the blastocrypt without fusellar covering. It seems, therefore, that graptoblasts were most probably lacking any internal portion of their blastothecae which could possibly be compared with the internal parts of a dendroid auto-theca. It is concluded that graptoblasts housed a zooid that never functioned as an autozooid, but suffered arrested development and encystation. The biological role of graptoblasts as dormant bodies is discussed.     

A REVIEW OF THE PROBLEMATIC OSTEOSTRACAN GENUS AUCHENASPIS AND ITS ROLE IN THYESTIDIAN EVOLUTION

Abstract:  The poorly understood osteostracan genus Auchenaspis , from the Upper Silurian of England, belongs to the thyestidians (Thyestiida), a controversial and important group that is key to the understanding of the evolution of the Osteostraci and paired pectoral fins. The two under-studied species of this genus are comprehensively reviewed using anatomical and novel statistical approaches. No reliable anatomical characters can be used to distinguish between the two species, yet discriminant analysis finds significant separation with respect to size. Potential causes of this conflict are discussed. The findings enable Auchenaspis to be considered in terms of wider thyestidian evolution and contradict previous interpretations of the genus as representing a paraphyletic taxon, whose morphology is intermediate between the general osteostracan condition and the highly derived tremataspids.