摘要:

The wrinkle layer the inner prismatic layer are described in three Triassic ceratid genera:Phyllocludiscites. Megaphyllites Proarcestes.Both layers have their counterparts in the shell wall of the recentNautilus:the wrinkle layer corresponds to the mantle‐adhesive layer the inner prismatic layer to the myostracal layer inNautilus.A detailed structural functional comparison between these layers is given. The wrinkle layer is also compared with the oblique prismatic layer in recent gastropod

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00732.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00733.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The kinds incidence of shell abnormalities were investigated in over 2000 adult Late Cretaceous scaphitid ammonites. Most are species ofHoploscaphites Discoscaphitesfrom the Maastrichtian Fox Hills Formation; for comparison, four older species ofScaphiteswere also studied. Four kinds of abnormalities vary in their incidence among the Fox Hills taxa but display no general trends. (1) Morton's syndrome, shell asymmetry unrelated to external injury, occurs in 3 to 6% of the Fox Hills scaphites. (2) Suture wander. veering‐off of the ventral lobe of the suture from the midline of the venter, occurs in most Fox Hills taxa with an incidence ranging from 1 to 11%. (3) Stretch pathology, an attenuation of the shell on the posterior part of the adult body chamber, is confined toHoploscaphifes nicolleti.(4) Externally inflicted injury, indicated by repaired damage on mature shells, has an average incidence of 10% in Fox Hills scaphites except in the stratigraphically youngestH. nebrascensis H. cheyennewiswhich approach 25 40% respectively. Good correlation between percent injuries adult size ornamentation is obtained only inDiscoscaphifes;all morphs of the co‐occurringHoploscaphitesdisplay nearly the same incidence of injuries regardless of their morphologic variation. The stratigraphically youngestH. nebrascensisbecomes larger more nodose simultaneously sustains more injuries. However, its dimorphH. cheyennensisremains morphologically unchanged although its incidence of injuries quadruples. These injury data, in themselves, do not support the hypothesis that predators were contributing more heavily to the mortality of Maastrichtian ammonites precipitated their extinct

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00734.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The literature of community paleoecology is filled with examples in which long‐term environmentally‐controlled faunal transitions are misidentified as forms of ecologic succession. This has obscured a fundamental community‐level process ‐community replacement‐ involving gradual to abrupt substitution of one benthic community for another as a result of subtle to sharp changes in habitats over subevolutionary time. In gradually changing environments, replacement takes place through conformational reorganization of species‐abundance distributions within established communities, yielding sequences of slightly different fossil associations. Environments that change very rapidly drastically feature a different type of community replacement involving species turnover, wherein environmental tolerance limits of community members are closely approached or exceeded. Paleoecologists should be alert to the strong likelihood that many temporal transitions involving autochthonous fossil associations are, in fact, community replacemen

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00735.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00736.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

Available data on the anatomy, ontogeny embryology of Brachiopoda (sensu lato) suggest that this Phylum in the traditional view is in fact a clade of organization includes two stocks of lophophorate organisms of quite different origins. Their rank does not correspond to existing Class divisions. The phosphatic‐shelled in articulates are regarded as a separate Class Lingulata. The Phylum Brachiopoda (sensu stricto) is restricted to the calcareous‐shelled inarticulate articulate lineages. Ancestors of the calcareous‐shelled brachiopods probably differentiated from the protolophophorates before the radiation of the other lophophorate stocks took place. The articulation of the valves appeared independently in several lineages during the early stages of brachiopod evol

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00737.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The CambrianOpabinia Anomalocarisare odd animals known mainly from the Middle Cambrian Burgess Shale.Opabiniahas usually been regarded as an arthropod, e.g. as a branchiopod crustacean. Parts ofAnomalocarishave been referred to three or four different phyla. Recent redescriptions have clarified much of their morphology resulted in their removal from the arthropods. Additional observations considerations indicate that the two genera have important similarities, including scale‐like structures arranged segmentally in transverse dorsal sets, which are separated by transverse tergal plates. Although external views are rare, traces of segmented appendages are identified inAnomalocaris.The animals are therefore again considered as arthropods, although they do not seem to be related to any of the other arthropod phyl

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00738.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The North American Upper Ordovician reference standard, the Cincinnatian Series, contains rich shelly microfossil faunas in its type area in the Cincinnati Region but graptolites are uncommon in most of its shallow‐water calcareous sediments. Consequently, the graptolite correlation of this key sequence has remained uncertain, in part, even controversial. A review of both previously published recently discovered graptolite Occurrences in the type Cincinnatian, combined with data from the important graptolite successions in Oklahoma New York‐Quebec, has not only clarified the graptolite correlation of the Cincinnatian but also added new data on the morphology taxonomy, the vertical horizontal distribution, of several taxa. The information now at hand indicates that the Edenian Stage correlates with theC. spiniferusZone, the Maysvillian Stage with theC. pygmaeuslower middleP. manitoulinensisZone, the Richmondian Stage with the upperP. manitoulinensis, theD. complanatus, possibly part of theC. inuitiZone. Comparison between graptolite conodont biostratigraphic evidence reveals no apparent conflict. Correlations are proposed between Upper Ordovician North American stages, graptolite conodont zones, successions in Texas, Oklahoma, Sweden, European graptolite zones, British ser

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00739.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

The silicified Wenlockian bivalve shells at Möllbos have been fragmented to a considerable extent. Shells which were broken prior to silicification exhibit possible original shell layers while those which were fragmented during laboratory treatment show no primary structures. The fauna at Möllbos was attacked by endolithic micro‐organisms. The borings of these were then coated with a carbonate envelope. After burial the unattacked original shell material was dissolved the envelope silicified. Later, empty moulds were subsequently filled with drusy calcite occasionally with quartz crystals. A third silicification went occurred at a later diagenetic stage when matrix had become lithif

ISSN:0024-1164    

DOI:10.1111/j.1502-3931.1986.tb00740.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY