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Seasonal changes in the morphometric and physiological parameters of the cockle Cerastoderma glaucum (Bivalvia) from the Baltic Sea (GD), the North Sea (LV), and the Mediterranean Sea (BL) were investigated. The cockles from GD were much smaller than those from other populations due to osmotic stress. The female to male ratios did not differ significantly from 1:1. The northern populations (GD, LV) had a monocyclic reproductive pattern, whereas the southern population (BL) seemed to reproduce throughout the year. Seasonal changes in the contents of biochemical components appeared to be correlated with changes in trophic conditions and the reproductive cycle. Protein content was the highest in spring for all the populations. The highest lipid contents and lowest carbohydrate contents were noted in GD and BL in spring, while no marked differences were noted among seasons in LV (probably because the data from both sexes were pooled). Respiration rates in GD were the highest among the populations, which could have been due to osmotic stress. High metabolic rates expressed by high respiration rates in GD and LV in spring and autumn could have resulted from gamete development (in spring) and phytoplankton blooms (in spring and autumn).
Three lithofacies characterize the Turonian/Coniacian sequences in the Upper Cretaceous of the Elbe Valley. The marly lithofacies, between Weinbohla - Dresden - Heidenau, consists of marls and calcareous clays (Strehlen Formation). A transitional lithofacies, with alternations of marls, clays and blocky sandstones, follows to the southeast (area between Rosenthal - Pirna - Lohmen). A sandy lithofacies, with blocky sandstones, is developed even farther to the southeast (Elbsandsteingebirge). The T/C boundary is situated in the lower part of the Strehlen Formation in the marly lithofacies, known from several boreholes. Coniacian index ammonites are absent across the T/C boundary in the three investigated boreholes apart from a deformed and incomplete specimen of Placenticeras cf. orbignyanum (GEINITZ). Therefore, bivalves must be used to place the T/C boundary. The Didymotis event II (Dresden-Marienhof Borehole), with Cremnoceramus waltersdorfensis (ANDERT), lies at the top of the Upper Turonian M. scupini Zone. The rarity or absence of the bivalve Didymotis in the Dresden-Blasewitz and Graupa boreholes is caused by facies changes. The FAD of Cremnoceramus rotundatus (TROGER non FIEGE), especially the C. rotundatus Event (Graupa Borehole, Hinterjessen Marl), can be used to place the T/C boundary. A small interval below the FAD of C. rotundatus and above the Didymotis II event, which may belong to the basal Coniacian, yields Cremnoceramus waltersdorfensis (ANDERT), Cremnoceramus waltersdorfensis hannovrensis (HEINZ), Mytiloides carpathicus (SIMONESCU) and Placenticeras cf. orbignyanum (GEINITZ). In the sandy lithofacies fossils are rare. It is not possible to place the boundary in either the Herrenleite Sandstone or in sandstone d. In the marly lithofacies of the Upper Cretaceous of Saxony bracketing of the T/C boundary is possible by means of planktonic foraminifera. It is possible to identify the evolution of planoconvex double-keeled globotruncanids of the Dicarinella hagni - Dicarinella primitiva - Dicarinella concavata group from the Upper Turonian. In the Dresden-Blasewitz and Dresden-Marienhof boreholes this group is represented in the T/C boundary interval by Marginotruncana paraconcavata PORTHAULT and Dicarinella cf concavata (BROTZEN). They are of rare occurrence because they are facies controlled. It is not possible to recognize the boundary between the scheegansi and concavata zones because of the restricted occurrence and rarity of the index forms in the investigated sections. In the Dresden-Blasewitz and Dresden-Marienhof boreholes the benthonic species Stensioeina granulata (OLBERTZ) was identified.
Taxonomic studies of Cretaceous inoceramid bivalves are confounded by high levels of intraspecific morphological variation within the group. Such variation is illustrated here using Cremnoceramus bicorrugatus s.s. (Marwick, 1926) from the lower Coniacian of New Zeland. This taxon displays a remarkable range of intraspecific variation that is the sum of three major components: 1) a basic set of ontogenetic transformations between the juvenile, immature and adult stages; 2) intra-populational variation in the relative timing or rate of developmental events; and 3) intra-populational variation in therate of absolute growth. The first of these components was largely genetically determined, whereas the other two were probably influenced by extrinsic environmental factors. Taxonomic interpretation of C. bicorrugatus s. s. is not possible without some understanding of both the basic ontogenetic plan and developmental variations within that plan. Interpretation is facilitated by the profound and step-wise nature of the ontogenetic transformations. In many other inoceramids, however, ontogenetic transformations are more subtle but may be subject to equally significant intraspecific developmental variations. Therefore, inoceramid taxonomists should describe not only total population variation, but also should document ontogenetic development in any species. In this way it is possible to identify basic ontogenetic plans, constrain likely limits to intraspecific variation, and distinguish intraspecific from interspecific morphological variation.
Content available remote General trends in predation and parasitism upon inoceramids
Inoceramid bivalves have a prolific evolutionary history spanning much of the Mesozoic, but they dramatically declined 1,5 Myr prior to the Cretaceous-Tertiary boundary. Only the enigmatic genus Tenuipteria survived until the terminal Cretaceous event. A variety of hypotheses have attempted to explain this disappearance. This study investigates the role that predation and parasitism may have played in the inoceramids' demise. Inoceramids show a range of predatory and parasitic features recorded in their shells ranging from extremely rare bore holes to the parasite-induced Hohlkehle. The stratigrahic record of these features suggests that they were virtually absent in inoceramids rior to the Late Turonian and became increasingly abundant through the remainder of the Cretaceous. These results suggest that predation and parasitism may have played a role in the inoceramid extinction, but more rigorous, quantitative data are required to test this hypothesis further.
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