摘要:

Severin, Kenneth P.&Lipps, Jere H. 1989 01 15: The weight‐volume relationship of the test ofAlveolinella quoyi:Implications for the taphonomy of large fusiform foraminifera.Lethaia, Vol. 22, pp. 1–12. Oslo. ISSN 0024–1164.Alveolinella quoyi, the largest living fusiform foraminifer, can be used to infer the paleobiology of extinct fusulinids and alveolinids. We measured test plus organic material weight, test weight, and test volume forA. quoyi, allowing the calculation of test density under various conditions. Tests have an average of 43% chamber space, and an average density of 1.5 gcm‐3. Living individuals can only fill an average of 39% of their chamber space with protoplasm. If they fill the remaining space with sea water, average effective test density is 0.953 gcm‐3, if the space is filled with a gas the density is 0.671 gcm‐3. Living individuals can withstand current velocities of 3–4 m sec‐1, velocities greater than commonly occur inA. quoyi'shabitat. Dead tests have lower effective densities than many carbonate sedimentary particles (0.508 g cm‐3if the chamber space is gas filled, 0.953 g cm‐3if it is sea water filled), making their settling velocities slow relative to similarly shaped and sized particles. Their large size and high traction velocities (>0.2m sec‐1) makes them unaffected by gentle currents which can remove 100–200 μ sized particles from the sediment. Their low settling velocity will tend to concentrateA. quoyitests during subsequent resuspension, creating a layer of tests near the sediment‐water interface. Concentrations of extinct fusiform foraminifera may have formed in a similar manner. □Lorger foraminifera, test weight, test vol

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01163.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Zhang, Xi‐guang, 1989 01 15: Ontogeny of an Early Cambrian eodiscoid trilobite from Henan, China.Lethaia, Vol. 22, pp. 13–29). Oslo. ISSN 0024–1164.Numerous phosphatized specimens from Xichuan, Henan, China permit a detailed study of the morphology and ontogeny of the Eady Cambrian eodiscoid trilobiteNeocobboldia chinlinicaLee. Several morphological changes of pygidia are seen to accompany growth, by means of which 13 quantitatively defined stages with a probable growth rate of 1.20, and 4 developmental periods (anaprotaspid, meta‐protaspid, meraspid. and holaspid) have been recognized for this species. The anaprotaspis is the first description for codiscoids. It shows great but gradual changes in morphology with progressive maturity. Morphometric and qualitative analyses indicate that three thoracic segments were formed regularly and then released from the pygidium during the meraspid period; and more than one instar might have occurred within a stage. The exoskekton consists of two well‐preserved layers, both bearing fine ornament that showed gradual change with growth as well. The free cheek with visual surface attached and the hypostoma show many of the fundamental characters of eodiscoids. Some morphological differentiation in cranidia may reflect a sexually dimorphic condition. Statistical and taphondmic analyses indicate that these specimens ofN. chinlinicamay represent a complete population. The larvae may have lived in swarms in a warm shallow water environment. □Trilobita, eodiscoid, morphology, ontogeny, paloeo‐ecology, Early Cambrian,

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01164.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Levinton, J. 1988:Genetics, Paleontology and Macroevolution. LX + 637 pp. Cambridge University Press. ISBN 0–521–24933 3. Price: U.S. $37.50 (bou

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01165.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Savazzi, Enrico 1989 01 15: Burrowing mechanisms and sculptures in Recent gastropods.Lethaia, Vol. 22, pp. 31–48. Oslo. ISSN 0024–1164.Burrowing was observed in 32 gastropod species, belonging to 8 families, from Italy and the Philippines. Most species burrow by repeating a three‐phase sequence: (1) digging with the foot, (2) dragging the shell forward and downward, and (3) rocking the shell around its longitudinal axis. Minor specific differences in the burrowing dynamics are common, and totally different mechanisms also occur. Burrowing sculptures consisting of terraces or asymmetrical tubercles are observed in the majority of the studied species. Characteristics of the burrowing process explain some cases of apparent divergence of burrowing sculptures from the paradigm. Burrowing sculptures in the Gastropoda should be expected to occur mostly among medium‐slender, rather than markedly high‐spired, shell morphologies. □Mollusca, Gastropoda, Cerithiidae, Nassariidae, Mitridae, Costellariidae, Conidae, Terebridae, Turridae, Hydro‐biidae, shell, sculpture, burrowing, functional morphology, ecology, behaviour, Holocene, Indo‐Pacific. Philippines, Medit

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01166.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Arua, Ingela&Hoque, Mominul. 1989 01 15: Predatory gastropod boreholes in an Eocene molluscan assemblage from Nigeria.Lethaia. Vol. 22, pp. 49–59. Oslo. ISSN 0021–1164.Morphometric data of 1, 346 boreholes belonging to eleven gastropod species and nine bivalve species have been studied. On the basis of hole‐wall geometry and concentricity of the inner and outer holes, six different borehole types are identified: (1) concave with concentric openings (A‐type); (2) concave with aconcentric openings (B‐type); (3) planar tapering with concentric openings (C‐type); (4) planar tapering with aconcentric openings (D‐typc); (5) vertical with concentric openings (E‐typc); and (6) concave‐planar with aconcentric openings (F‐type). The preferred gastropod and bivalve prey species for each bole type are named. In identifying the borers of a particular hole type, the mode of life of the most preferred prey species is used as a diagnostic parameter. Preferred infaunal prey species are dominantly bored by naticids, preferred epifaunal prey is mainly bored by muricids. The presence of a boss at the base of an inoomplete hole and the presence of countersunk holes are the additional criteria for identifying naticid borings. The hole type analysis suggests that hde types A, B and D belong to muricids and C, E and F to naticids. All the naticid and muricid hole types studied have a preferred site for boring. They are located purposefully where they would intercept internal organs of the prey. It appears that in ornamented bivalve shells these predators would rather drill between ribs than on top of the ribs. □Gastropoda, predation, boreholes, molluscan assemblage, Eocene. Ameki Formation, Nigeria. Ingela Arua, Department of Geology, University of Nigeria, Nsukka. Nigeria; Mominul Hoque, Geo‐Mechanis Inc., Elizabeth, PA 15037, U. S.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01167.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01168.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Simms, Michael J. 1969 01 15: Columnal ontogeny in articulate crinoids and its implications for their phylogeny.Lethaia, Vol. 22, pp. 61–68. Oslo. ISSN 0024–1164.Detailed doamentation of columnal ontogeny in several Lower Jurassic isocrinids reveals a number of features which are of phylogenetic significance. Columnal proportions are determined by two largely independent growth vectors. Columnal diameter is primarily a function of cup size at the time of formation, though it may subsequently undergo considerable increase through lateral accretion. Columnal height is largely independent of cup size except for a gradual increase with the growth of the whole animal. Columnal diameter increases at a much greater rate than columnal height and so columnals are relatively lower in large individuals. Heterochronous variation in vertical growth rate or the extent of lateral accretion in columnals may significantly alter their shape. The smallest isocrinid columnals found (0.35 mm diameter) have synarthrial articula. The transformation to a typical pentaradiate symplexy, via a triradiate stage, occurs at a diameter of about 0.75 mm. Synarthrial articula are unknown in millericrinid columnals, which instead have symplectial articula at small diameters (0.45 mm). The presence of synarthrial articula in the stems of juvenile isocrinids, and their absence in millericrinids. supports previous hypotheses concerning derivation of bourgueticrinids from an isocrinid, rather than a millericrinid, ances

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01169.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Pandolfi, John M.&Burke, Collette D. 1989 01 15: Environmental distribution of colony growth form in the favositidPleurodictyum americanum. Lethaia, Vol. 22, pp. 69–84. Oslo. ISSN 0024–1164.Colony growth form is of fundamental importance to understanding the ecology of both modern and ancient marine sessile colonial animals. Fourier shape analysis of the coralPleurodictyun americantum(Tabulata: Favositida) from the Middle Devonian Hamilton Group of New York State, indicates that colony growth form is variable between environments. Discriminate function analysis of harmonics 2–6 of 51 assemblages ofPleurodictyum americanum(N = 1900) shows that this species displays an onshore to offshore gradient in colony shape. Offshore environments characterized by low levels of turbidity, oxygen, and light contain more flattened, less hemispherical growth forms, whereas onshore environments characterized by high levels of turbidity, oxygen, and light contain more hemispherical, less flattened growth forms. Harmonic shape analysis detected subtle differences among samples ofP. americanumfrom different environments, but also showed that distinctive morphotypes are distributed within horizons. as well as between them. In fact, no one‐to‐one correspondence in growth form to environment is apparent; growth forms are distributed within environments, suggesting that genetic factors may have had a greater influence over coral growth form than environment. In tabulate corals, patterns of within species variability must be determined before growth form may be useful in interpreting ancient environments. □Tabulate coral, Fourier shape analysis, morphological variability, growth form, Devonian, Hamilton Grou

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01170.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Wood, Rachel, Reitner, Joachim&West, Ronald R. 1989 01 15: Systematics and phylogenetic implications of the haploslerid stromatoporoidNewellia miranov. gen.Lethaia, Vol. 22, pp. 85–93. Oslo. ISSN 0024–1164.The presence of spicules in a Palaeozoic stromatoporoid is here confirmed.Parallelopora miraNewell, 1935 from the Upper Carboniferous of the U.S.A. is redescribed as a calcified haplosclerid sponge with a primary siliceous spicule framework of isodictyally arranged styles, sub‐tylostyles and strongyles and a secondary calcareous skeleton of stromatoporoid grade and probable aragonitic original mineralogy.P. mirais placed within a new genusNewellia, and family, the Newellidae. This form is postulated to have possessed large amounts of collagenous organic material which enveloped and bound the spicular framework in place. By the draping outline of the calcareous skeleton around the spicule framework and by analogy with the Recent demosponge genusVaceletia, the calcareous skeleton is suggested to have formed by the direct mineralization of this collagenous template.Newellia miranov. gen. is further proposed to constitute a member of a new clack of haplosclerid stromatoporoids, together withEuz‐Miella erenoensis(Lower Cretaceous); a clade with some similarity to Recent non‐calcified forms, e.g.Adocia. Most notably, the presence of different calcareous skeleton mineralogies and possibly microstructures in these two forms suggests the independent development of a calcareous skeleton at different times within this spicule clade. Demosponges appear to have produced calcareous skeletons independently in many different spicule clades. Calcified demosponges are now known from the Hadro‐merida (Lower carboniferous; Upper Cretaceous ‐ Recent), Axinellida (Upper Triassic ‐ Lower Cretaceous; Upper Cretaceous; Recent), Poecilosclerida (Recent) as well as the Haplosclerida (Upper Carboniferous ‐ Lower Cretaceous; Recent).□Upper Carboniferous, stromatoporoid, spicules, haplosclerid demosponges, calcareous skeleton biomineralization, demospong

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01171.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Checa, Antonio&Westermann, Gerd E. G. 1989 01 15: Segmental growth in planulate ammonites: inferences on costal function.Lethaia, Vol. 22, pp. 95–100. Oslo. ISSN 0024–1164.In planulate Ammonitina, the directions of costae and their parts coincide with the growth lines, both being accreted in parallel and subtriangular increments, i.e. segments. This implies that the growing margin was consistently corrugated (plicated) parallel to the edge of the peristome. The adventral separation of the ribs caused by the coiling increased with whorl involution and was compensated for by costal division into primaries and secondaries. We propose that costation of the shallow‐water, nekto‐benthic plandates reduced the stiffness and increased effective thickness of their growing peristome. Ribs functioned (primarily or secondarily) as a protection for the immature, fragile aperture against predators and impacts.□Ammonite shell, Jurassic, morphology, growth lines, ornamentatio

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1989.tb01172.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY