摘要:

The Ludlow Series of Wales and the Welsh Borderland represents an ocean‐bordering basin and shelf which received a shoaling sequence of sediments in the late Silurian. Graptolites grade from highest diversity and density in basin areas to lowest diversity and density on the nearshore shelf. By analogy with modern zooplankton, this distribution is attributed to differentiation of surface water masses over basin and shelf. During Ludlow time, the center of graptolite abundance shifted northward, indicating a restriction and seaward movement of the basin water mass. Small nektic cephalopods and phyllocarids parallel distribution trends of the graptolites, as does a fauna of small bivalves and brachiopods which may have lived on floating plants. The water mass model accounts for most distributional patterns of pelagic organisms in this local area, and has broader application to the distribution and evolution of graptolite

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00622.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

Over 50 species of liparoceratid ammonites have previously been recognized from theIbexandDavoeiZones (Lower Pliensbachian, Lower Jurassic) of England alone. Such a high specific diversity is an artifact caused by their stratigraphical importance and the complex nature of their shells. Simple bivariate analysis indicates thatAegocerasspecies are arbitrary subdivisions of an allometric growth trend. Principal component multivariate analysis shows thatLiparocerasandAndrogynoceras (sensuCallomon) are quite distinct fromAegoceras, and they display a more random pattern of variation. The existence of stratigraphically useful size changes in liparoceratids mirrors precisely size increases in benthic molluscan taxa, such as the bivalve‘Astarte’ platymorphaand the archaeogastropodEucyclus subimbricata.The ammonite size changes, at least, probably result from phenotypic variation analogous to that observed in the living cephalopodSepia officinalis.This evidence taken in conjunction with the fact that kosmoceratid ammonite size changes correspond somewhat with benthic faunal changes suggests that ammonites maybe less useful for stratigraphy than is belie

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00623.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The lower Middle Ordovician carbonate sediments of the Georgina Basin in Australia contain many and varied Actinoceratida, including an endemic family, Georginidae Wade (1977), with siphuncular calcification consisting of radial lamellae separated by spaces (now sediment‐filled) enclosed within calcified annulus walls. In each segment a distinct series of more massive calcareous engrafts grows inward from the inside of the connecting ring and is engrafted into adjacent annuli across the interannulus; this divides the perispatium into longitudinal perispatial sinuses. At each extremity each perispatial sinus is connected with passages leading through the segments to the axial space and, nearer to, or at the interannulus, with radial canals. Axial canals are few, but more than one is normal. Good preservation ofArmenocerasandActinocerasallows recognition of similar structures in the annuli of normal Actinoceratid

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00625.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00626.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The first unequivocal fossil echiuran,Coprinoscolex ellogimusgen. et sp.n., is described from the Middle Pennsylvanian Francis Creek Shale of the Mazon Creek area of northeastern Illinois. Specimens are whole‐body impressions within siderite concretions. They show anterior proboscides, cigar‐shaped trunks, convoluted alimentary canals, and cylindrical pellets. Lack of setae suggests classification in the Family Bonelliidae.Coprinoscolexwas most likely a marine deposit‐feeder, either crawling over the sediment surface or burrowing to shallow depths while ingesting sediment. While this occurrence does not confirm or deny an annelidan ancestry for the Echiura, it indicates that by the Pennsylvanian, echiurans were unsegmented and essentially modern in

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00627.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00628.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

The ontogenetic development of two Recent scleractinian corals,Golaxea fascicularis(Linnaeus) andAcrhelia horrescens(Dana), has been studied in serial thin sections. The origin of the septotheca (a collective term including both eutheca and pseudotheca) is reconsidered. The eutheca is found to be a basic skeletal structure of corals and of primary origin, formed directly from the basal plate, not by the thickening of septa. The eutheca prepares the way for the formation of metasepta. The ontogenetic growth of the metasepta is illustrated. The pseudotheca is formed by fusion of neighbouring septa and is entirely of secondary origin. Its development is occasional. The essential mural structure of oculinid corals with pseudothecal walls is euthecal.

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00629.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00630.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1977.tb00631.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY