Showing papers in "Lethaia in 1979"

Phosphatocopine ostracodes with preserved appendages from the Upper Cambrian of Sweden

Abstract: Mulkr. Klaus 1. 1979 01 IS: Phosphatocopine ostracodes with preserved appendages from the Upper Cambrian of Sweden. Lethaia. Vol. 12. pp. 1–27. Oslo. ISSN 0024–1164. More than 400 specimens of phosphatocopine ostracodes. representing different moult stages of Vestrogothia. Falites and Hesslandona have been recovered, with body and appendage structures preserved in minute detail. from anthraconites in the Upper Cambrian of Sweden and drift boulders deriving from that area. The secondary phosphatization of these structures, leading to preservation. is extensively discussed. It comprises even the inner lamella, but the abdomen is not preserved. Hypostome and lower lip are well developed. The large antennula is composed of a basipodite with probably two podomeres and a long exopodite with up to 18 podomeres bearing long spines, forming a natatory organ, and a broad endopodite of two to three podomeres. The biramous organization of the antennula is a unique, most primitive feature of phylogenetic significance. The antennae and up lo four additional pairs of appendages are also biramous and similar to the antennulae, not yet differentiated for specialized functions. Only the last pair is uniramous, but a second branch may have developed in subsequent moult stages not represented in the material. The movement of food into the mouth was achieved by the endites of antennulae and antennae, a function transferred backwards to other appendages during the course of ostracode phylogeny and reflected in ontogenetic trends among Recent ostracodes. The phosphatocopines were nectobenthic, filtering plankton feeders.

Cavity-dwelling organisms in Lower Cambrian patch reefs from southern Labrador

Abstract: An intact and well-preserved biota of cavity-dwelling organisms (coelobionts) of early Cambrian age is found within growth-framework cavities in archaeocyathid patch reefs of the lower Forteau Formation (upper Bonnia-Olenellus Zone) of southern Labrador. The biota was diverse, and consisted of encrusting and vagrant organisms. Renalcis, a Renalcis-like form, Epiphyton, Girvanella, and Serligia, all lived attached to walls and roofs of the cavities; other attached forms were Bija, Archaeotrypa, and two types of Wetheredella, an agglutinated foraminifer. Other organisms, including trilobites, probable calcareous ostracodes, brachiopods, echinoderms, and worms, as well as fungi, are also found preserved within the cavities. The structure of the coelobiontic community is surprisingly modern; it indicates that as early as the Lower Cambrian coelobiontic organisms were well-established in reefs, and were an important part of the reef community as a whole.

Functional morphology and palaeontological significance of the conchiolin layers in corbulid pelecypods

Abstract: The Corbulidae, which today are slow, cumbersome, very shallow burrowers, developed special morphological features by which they obtained an outstanding capability to withstand the physical and biological stresses characteristic of their preferred habitat. These features are: an inequivalve, globose shape, thick shells, and conchiolin layers (at least one) embedded within their valves in a unique way. These features enable the corbulids to close their valves tightly during the unfavourable environmental conditions (e.g. low salinity, low oxygen content) which may prevail in the marginal marine regions inhabited by several corbulid species. The conchiolin layers act as a barrier preventing all chemically boring organisms from penetrating into the bivalve shell, or shell dissolution by sea water undersaturated with respect to calcium carbonate. The layered conchiolin weakens the shell mechanically, however, especially during fossilization, when the conchiolin is decomposed. The valve splits apart into two shells so completely different in appearance that they may be attributed to different taxa. The conchiolin layers are therefore of great ecological and palaeontological significance. The nature of these conchiolin layers in Corbula (Varicorbula) gibba (Olivi) is described and illustrated and their functional significance discussed in relation to other living and fossil corbulid species.

Dinosaur stampede in the Cretaceous of Queensland

Abstract: Numerous and well-preserved trackways in mid-Cretaceous sediments of West Central Queensland, Australia, are attributed to a stampede of small to medium-sized bipedal dinosaurs - both herbivores (ornithopods) and minor-league predators (coelurosaurs). The tracks of a single large predator (carnosaur) suggest a reason for the stampede. These trackway data permit calculation of sustained running speeds for the coelurosaurs and ornithopods.

Transgression, regression and fossil community succession

Abstract: Recent paleoecological studies have emphasized the recognition of successional stages of level-bottom communities, but have neglected to point out techniques for distinguishing succession within a fossil community from the temporal and spatial replacement of one fossil community by another. The physical integrity of a marine level-bottom community is discernible, in most instances, through careful temporal and spatial study, and one community can be distinguished from another by judicious application of the ‘end-member’ concept. Community boundaries are only as distinct as the associated environmental stress gradient. Of first-order significance in understanding fossil community succession and replacement is appreciation of the basic asymmetry of the community dynamics involved in transgression-regression events. Of second-order importance is appreciation of the nature of the onshore-offshore environmental stress gradient, which, in turn, is controlled by the physical setting of transgression-regression (e.g. progradation versus eustatic control; high topographic relief versus low topographic relief, etc.). The application of the preceding concepts is shown by detailed study of community succession and replacement in the Cambridge Limestone (Upper Pennsylvanian), Guernsey County, Ohio.

The earliest vascular land plants: continuing the search for proof

Abstract: New collections from Bringewoodian strata (Silurian, Ludlow Series, Saetograptus leintwardinensis incipiens Zone) in Wales have yielded the oldest known specimens of the plant Cooksonia. From evidence at younger (Eř;eoli/Downton) horizons this genus is considered to be a vascular plant; although no tracheids have been isolated from the Bringewoodian specimens, on the basis of comparative morphology they are concluded to be the oldest recorded tracheophytes. The types of evidence relevant to the identification of vascular plants are briefly reviewed, and the relationships of the Welsh Cooksonia flora to other late Silurian floras are discussed. Confident stratigraphical dating is a prerequisite for any discussion of early plant evolution, emphasising the desirability of an integrated approach incorporating both geologial and palaeobotanical investigations. The dating of two published records of diverse Silurian floras, including lycopods, is questioned; recent dating of the Australian Baragwanathia flora as early Ludlow on the basis of graptolites is not supported by the shelly faunal evidence, which indicates a correlation within the Lower Devonian.

Early Cambrian provincialism and biogeographic boundaries in the North Atlantic region

Abstract: Early Cambrian lithofacies and their stratigraphic context, characteristic of a number of tectonic elements within the North Atlantic region, are interpreted with respect to depositional environment and related trilobite provincialism. Faunas of the North American province are typically indigenous to shallow, warm water on a sand-carbonate shelf on the North American craton; those of the Scandian province to shallow cold water with predominantly clastic deposition on the European platform; those of the Avalonian province to shallow cold water with predominantly clastic deposition fringing islands and rises on the Iapetus Ocean floor; Intermediate zone faunas, consisting of North American, Avalonian and endemic elements, to the slope or margin of the North American shelf; faunas of the Tethyan province to a shelf bordering Gondwanaland ranging from warm to cold at different times and different places, and under some Avalonian influence in the later Early Cambrian; and a pelagic realm characterized by agnostids. Biogeographic boundaries are related to the position of the thermocline and to light regimen, which determines the biogeography of autotrophs and hence of provincial niche structure. Provincialism is determined by gross environmental differences reinforced by biotic factors.

Conodont element function

Abstract: There are close similarities between conodont elements and teeth both in general shape and in that they possess pointed tips and have expanded bases with more porous tissue. A number of examples of conodont elements which parallel specific kinds of tooth shapes and organizations are added to earlier known similarities. Both in teeth and in conodont elements the surface structures include cutting edges, striations, and barbs. The change in strength of the conodont denticles caused by the evolution of white matter is also shown to agree with a tooth function. On the other hand, the elements grew throughout the life of the animal by lamellae added to the surface. The solution of this paradox is found in the elements alternating between a growth phase and a functional phase. During growth the oral surface of the elements was enveloped in folds of secreting soft tissue. Structures henceforth termed burrs were formed at the contacts between the folds. Parts of the burrs evolved into cutting edges. Three different bite types occurred among the conodont elements. Many (all?) conodonts were predators which used their elements to seize and to process the food mechanically. The shape of the conodont elements cannot be used for conclusions regarding the affinities of the conodonts. Similarly, an identification of a fossil as belonging to the conodonts must be supported by other evidence than just shape.

The structure and evolution of Ordovician conodont apparatuses

Abstract: Multielement taxonomy was instituted for Ordovician conodonts over a decade ago, and probably a majority of the multielement genera have been defined or are well understood. The present systems of notation for elements within apparatuses are inadequate and cumbersome. A new notation scheme is proposed which applies a single-letter code to the position in the apparatus occupied by certain element morphotypes. The taxonomic status of all known Ordovician conodont genera is reviewed (appendix) using the new notation, and a new scheme to classify conodont apparatuses is presented. Five main apparatus types (I-V) and seventeen subtypes (IA-IC, etc.) are defined. Within these groups, all known Ordovician conodont genera can be accommodated, and probably few new groups are required to include all other conodont genera. The apparatus types and subtypes are defined on the basis of symmetry, curvature, and number of the element types, with a clear distinction being made between the first and second transition series. Certain homologous relationships, both between and within many apparatus types, are noted. The evolution of the five major types, and the subtypes, is traced through the Ordovician. The pattern of evolution suggests that the types and subtypes recognized are probably natural biologic groupings, largely reflecting phylogenetic change.

The environmental significance of Lingula in the Ludlow Series of the Welsh Borderland and Wales

Abstract: Cherns. Lesley 1979 01 15: The environmental significance of Lingula in the Ludlow Series of the Welsh Borderland and Wales. Lethaia. Vol. 12. pp. 35–46, Oslo. ISSN 0024–1164. The inarticulate brachiopod Lingula is commonly regarded as an indicator of very nearshore environments, particularly when found in monospecific assemblages. However, neither of the two common species in the Lower Leintwardine Beds, L. lewisii and L. lata. which occur commonly in such associations, have distributions indicative of such an environment. Their Occurrence correlates closely with the Leintwardinian palaeogeography. The former species is concentrated in shelf areas, the latter is confined to the basin; the two distributions overlap little. Individuals of both species are found articulated and perpendicular to the bedding, apparently in situ. Hence, the species may be inferred to have equivalent, infaunal modes of life comparable to living representatives of the family. The basinal distribution of L. lara is an original feature. The depth of the actively subsiding basin was relatively great, judging from sedimentological and palaeogeographical evidence. Therefore, L. lata was a species adapted to ‘deep-water’ environments. The lingulid distributions, reviewed against the concept of brachiopod depth-related communities previously defined for the Ludlow show the latter to be inapplicable in the Leintwardinian. The depth significance postulated for the recurrent species associations typical of the shelf sequences cannot be accepted.

The inference of extrazooidal feeding currents in fossil bryozoan colonies

Abstract: Taylor, Paul D 1979 01 15: The inference of extrazooidal feeding currents in fossil bryozoan colonies Lethaia, Vol 12, pp 47–56 Oslo ISSN 0024–1164 Previous studies on live bryozoan colonies have shown that the feeding autozooids in a colony may cooperate in differing ways to produce an extrazooidal watercurrent system organised on a colony-wide or subcolony-wide basis The presence of an extrazooidal current system may be inferred in fossil stenolaemate bryozoans which exhibit either a differential spacing of open autozooecial apertures or a systematic variation across the marial surface in the orientation of automoecial distal portions By inference, aggregations of autozooecial apertures represented loci of inhalant extrazooidal flow whereas zoarial protuberances (eg monticules) with outwardly leaning autozooecia acted as loci of exhalant extrazooidal flow Bryozoans having automoecia opening obliquely into gaps or fenestrules in their zoaria probably drew a unidirectional extrazooidal current of water through the fenestrules Extrazooidal water currents may function to accelerate colony clearance rate, decrease the chances of recycling filtered water, aid spermatoman and larval dispersal, and clear sediment from the colony surface

An echiurid worm from the Late Precambrian

Abstract: A description is given of the first Precambrian echiuroid worm, from the Kuibis Quartzite of the lower Nama Group of southwest Africa (Namibia), Protechiurus edmondsi gen. et sp. nov. The occurrence of ridges on the cast, suggesting the presence of longitudinal muscle bands on the surface of the body, supports assignment to the living family Echiuridae. Their mode of life and environment are compatible with the palaeoecology of the Late Precambrian fauna of the Kuibis Quartzite.

Aspects of hadrosaurian cranial anatomy

Abstract: Supraorbital bones in Saurolophus angustirostris are described, and their presence in all hadrosaurs is suggested. Frontal-nasal and premaxillar-nasal fontanellae are distinguished in hadrosaurs; their presence is explained as connected with growth and considered to he responsible for the variability of crest structures. New data indicating the presence of a cartilaginous diverticulum nasi within the circumnarial depression in Saurobphus ongustirostris are presented. A physiological (respiratory and/or thermoregulatory) function of the nasal diverticulum is proposed.

Structure and secretion of the carapace in some living ostracodes

Abstract: The carapaces of some living freshwater and brackish-water ostracode species have been studied by means of light microscope, scanning electron microscope. transmission electron microscope, electron probe analyzer and X-ray diffractometer, with emphasis placed on the ‘pigment’ granules. The granules were found to consist of calcite and apatitic calcium orthophosphate. They are located within the epidermis, as a layer which is attached to the internal side of the calcite layer. It is suggested that the main function of the granules is the construction of the new calcareous valve in the moulting process. The layer of granules probably recrystallizes to form the calcite crystals of the valves.

Enrollment in the classification of trilobites

Abstract: Enrollment is not as fundamental a character complex for the classification of Trilobita as Bergstrom (1973, Fossils and Strata 2; 1977. Lethaia 10) has claimed. Different enrollment styles occur within accepted monophyletic taxa, which cut across Bergstrom's (1973) classification and which support the concept of the Order Proetida Fortey & Owens, 1975. False phylogenetic relationships are deduced from unjustified a prior; assumptions about the nature of primitive and derived character states. Einrollung ist kein so grundlegendes Merkmal fur die Klassifizierung der Trilobiten, wie dies Bergstrom (1973, Fossils and Strata 2; 1977, Lethaia 10) gefordert hat. Das Auftreten verschiedener Einrollungs-weisen innerhalb anerkannter monophyletischer Taxa durchkreuzt namlich seine Klassifizierung (1973), stutzt aber die der Aufstellung der Ordnung Proetida Fortey & Owens 1975 zugrundeliegende Auf-fassung. Unrichtige apriori-Antworten auf die Frage, was primitive und was sekundare Merkmale sind, fuhren zu irrigen Folgerungen uber phylogenetische Zusammenhange. L'enroulement n'est pas, pour la classification des Trilobites, un ensemble de caracteres aussi fonda-mental que Bergstrom(1973, Fossils and Strata 2; 1977. Lethaia 10)a bien voulu le dire. Differents styles d'enroulement sont presents chez des taxa reconnus comme monophyletiques ce qui ne correspond pas a la classification de Bergstrom (1973) mais vient a I'appui de I'Ordre Proetida Fortey & Owens 1975. Des distinctions a prior; et insuffisamment fondees entre caracteres primitifs et caracteres evolues conduisent a l'establissement de relations phylogenetiques erronees.

The Devonian land plant Protosalvinia

Abstract: Gray, Jane&Boucot, ArthurJ. 197901 15: The Devonian land plant Protosalvinia. Lethaia. Vol. 12, pp. 57–63. Oslo. ISSN 0024–1164. Protosalvinia (=Foerstia) shows a number of morphological features which suggest that it was a land plant, possibly an emergent aquatic. Certain kinds of biochemical data, as presently interpreted, also support the morphological evidence. The weight of evidence supports neither a fucoid nor even an algal attribution for this enigmatic plant. Protosalvinia should be treated as the representative of a separate group of land plants, as previously advocated. Tracheid-like tubes with internal spiral thickenings appear on the basis of direct comparison to be morphologically identical to those of nematophytalean origin. They may have functioned in a capacity similar to the tracheids of vascular plants. The Nematophytales are non-marine plants of uncertain taxonomic position.

Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico

Abstract: Toomey. Donald F. & Cys. John M. 1979 01 15: Community succession in small bioherms of algae and sponges in the Lower Permian of New Mexico. Lethaia, Vol. 12. pp. 65–74. Oslo. ISSN 0024–1164. Small organic mounds outcrop in the Lower Permian Laborcita Formation of the northern Sacramento Mountains of southcentral New Mexico. These small organic structures, up to I'm in height and 3 m in diameter, are unique because they show a well developed vertical biolic zonation. This zonation consists of an initial pioneer community composed of small digitate or plumose colonies of algae and foraminifers (Stage 1). This is followed by a climax community that is first dominated by laminar colonies of the red alga Archaeolithophyllum (Stage 2). and followed by a terminal community composed of minor Archaeolithophyllum, erect heliosponges and brachiopods, dominated by the form Composita (Stage 3). Evidence suggests that the mounds initially developed in shallow water within an open lagoon but. with continued transgression and rapid deepening of the depositional environment. the biota responded to the changes. The organic buildups were killed off by sudden influx of clastics from a tectonically active nearby landmass.

Environmental variation in a fossil scleractinian coral

Abstract: Sample populations of Solenastrea fairbanksi, collected from different environments in the Pliocene Imperial Formation, can be distinguished by measurements of linear dimensions of the coenosteum and thickness of septal structures. In these characters, magnitudes of intercolony variance components are lower than interpopulation or intracolony components, suggesting that the variation is largely caused by environmental factors. Three patterns of mean variation exist between populations: (1) Highest means occur in shallow, offshore (high energy) environments. (2) Highest means occur in shallow environments with low turbidity (high light intensity). (3) Highest means occur in clear, deeper offshore environments (favorable nutrient supply). The distance between adjacent corallites and the inverse of coenosteal porosity follow the first pattern, measures of thickness of vertical corallite structures follow the second, whereas estimates of annual growth rate follow the third. Corallite diameters and columella thicknesses do not vary between populations. Comparisons with modern species show that many characters in S. fairbanksi respond to environmental factors in a manner different from similar characters in other scleractinian species. In fact, some inflexible characters in S. fairbunksi are highly flexible in other species.

Eccentricity in the clypeasteroid echinoid Dendraster: environmental significance and application in Pliocene paleoecology

Abstract: Stanton, Robert J., Jr., Dodd, J. Robert & Alexander, Richard R. 1979 01 15: Eccentricity in the clypeasteroid echinoid Dendraster: environmental significance and application in Pliocene paleoecology. Lethaia. Vol. 12, pp. 75–87. Oslo. ISSN 0024–1164. The echinoid Dendraster lives in the northwest Pacific in environments ranging from open exposed coast to protected embayment. Water energy and the abundance and quality of food along this environmental gradient are correlated with test size and eccentricity of the apical area, so that larger and more eccentric specimens occur on the open coast than in bays. Study of Dendraster in Pliocene strata of the Coalinga California region indicates that these morphologic characteristics provide valuable information for paleoenvironmental reconstruction. Lateral and temporal environmental gradients within a broad Pliocene embayment and the location and size of the bay entrance can be determined on the basis of Dendraster eccentricity and size. Several species and subspecies of Dendraster in the Pliocene of the Coalinga region, described largely by differences in eccentricity, are probably not valid taxa but are merely ecophenotypic expressions of the laterally and temporally variable environment.

Demosponges as Substrates: an Example from the Pennsylvanian of North America

Abstract: The rigid skeletal frameworks of two heliospongid genera from the Bethany Falls Limestone (Pennsylvanian) of Missouri provided suitable sites of attachment for other marine invertebrates in a quiet water environment. A cluster of three horn corals attached apically to one Heliospongia while it was upright. Other horn corals are in lateral contact with ?Coelocladiella fragments and may have attached to fallen specimens. The distribution of acrothoracic barnacle borings and membraniporiform bryozoans on ?Coelocladiella fragments suggest that the sponges were in an upright position when the epizoans lived. Calcareous worm tubes and shell scars of Derbyia are also associated with ?Coelocladiella. The sponges themselves became established on a soft carbonate mud bottom by growing on productacean shells and possibly fallen blades of calcareous algae. Irregularities in their form indicate that conditions were crowded on limited sites of attachment. The organisms in the assemblage are ecologically coherent and in situ. Ecological requirements of associated organisms and sponge morphologies indicate: (1) the energy of the environment was low to moderate, (2) the rate of deposition was slow and (3) the substrate was a soft carbonate mud.

The origin of the spiriferidine brachiopods

Abstract: Wright, Anthony D. 197901 15: The origin of the spiriferidine brachiopods. Lethaia. Vol. 12. pp. 29–33. Oslo. ISSN 0024–1164. In recent years doubts have been expressed as to whether the strophic spiriferidines should continue to be grouped with the non-strophic spiriferids in the order Spiriferida or not. The solution to this problem will only be found by establishing the origin of the spiriferidines. A characteristic feature of the spiriferidines is their well developed micro-ornament; this is shared also by the orthid Platystrophiinae, and together with the striking similarity in overall morphology (well recognized in the early nineteenth century) it suggests that here, in the Platystrophia plexus, is the ancestral stock of the strophic spirebearers. The Platystrophunae share with the non-strophic Rhynchonellida the potential to develop a spire. It is here considered that the former gave rise to the spiriferidines and the latter to the non-strophic spire-bearers. These quite separate developments justify the separation of the spire-bearers into the two orders Spiriferida and Atrypida.

Evolutionary ecology of nine sympatric species of the pelecypod Limopsis in Cretaceous chalk

Abstract: The ecology and functional morphology of nine species of Limopsis that lived together in muddy bryozoan bioherms in the Cretaceous of Denmark are discussed. Two independent lines of limopsids entered the white-chalk environment: a non-byssate line represented by one flat circular burrowing species and abyssateline which gave rise to the formation of eight species. Seven of these, ranging from a large globose infaunal species to a small mytiliform epibyssate monomyanan, constitute a morphocline. The morphocline reflects adaptations along an environmental gradient, possibly related to substrate size and water flow. The morphocline contains two dominant species. One of these is epifaunal and the other infaunal, which demonstrates a trophic-group distribution sensu Turpaeva, reducing competition. A third, infaunal, species - not a member of the cline - reached a level of dominance, too, which underlines the evolutionary distance between this species and those of the morphocline. The sympatrical formation of the species appears to have taken place through specific habitat selection, resulting in non-competitive units. The morphological modifications resulted in a series of species ranging from near isomyarian forms over increasingly heteromyarian species to a monomyarian species, a unique case within the arcids.

A spathognathodont lineage of Mississippian conodonts

Abstract: Evolutionary lineages of conodont elements and of some apparatuses are gradually being documented to increase the value of these fossils in stratigraphic interpretation and to further our understanding of conodont taxonomy. The well-documented faunas from Mississippian strata of the Illinois Basin and type Mississippian beds provide a great deal of information for the recognition of phylogenies. The disjunct element genus Spathognathodus is part of a basic and long-ranging type of conodont apparatus from which a number of other forms have been derived, and some of its Mississippian disjunct element species can now be placed in multielement species. A lineage involving spathognathodont Pa elements recognized in the Mississippian, then, is the basis of the present study. The phylogeny recognized started with Synprioniodina? crassidentata, and includes S.? regularis, S.? pulchra, S.? coalescens, S.? spicula, Hinduodus cristula, and H. minutus in the Mississippian. Aputiignathus scitulus and A. penrscitulus apparently represent a separate line, which also might include disjunct element Spathognathodus rexroadi.