Interstitial bryozoans

50 p. : ill. ; 26 cm.Includes bibliographical references (p. 46-50)."A unique fauna of interstitial bryozoans has been found encrusting sand substrata on a high-energy shoal off the Atlantic coast of Florida. This fauna includes juveniles of two species of free-living cupuladriids, as well as nine new species (one new genus) apparently adapted to interstitial conditions and characterized by small size, simplified colony structure, and very early reporduction. Other species known from larger substrata were also found encrusting interstitial sand and shell grains at Capron Shoal. The 'interstitial refuge' may be importnat in explaining the broad species distributions of encrusting bryozoans along mostly sandy continental shelves"--P. [1]

Population structure of colonial organisms. A palaeoecological study of some free-living cretaceous bryozoans

It is shown that application of standard size-frequency procedures can be as rewarding in palaeoecological studies of colonial organisms - exemplified by two free-living Cretaceous bryozoans, Stichopora pentasticha and Lunulites mitra - as has been generally recognised in studies of non colonial organisms. In spite of clear differences in their mode of life both analysed species are found to have population structures largely analogous to most solitary, benthonic invertebrates ; i. e. they were subject to high juvenile mortality, and probably, decreasing growth rates. Onset of sexual maturity, on the other hand, differs in the two species, no doubt reflecting their different habits. Since no ways of determining absolute age-size relationships have been found, survivorship curves cannot be constructed. Nevertheless, detailed considerations of the size-frequency distributions in combination with functional morphological inferences do provide important information about variations in growth and mortality rates in relation to the ontogenetic development.Pour étudier la relation taille-fréquence les méthodes classiques utilisées pour des organismes non coloniaux ont été employées pour des études paléoécologiques d'organismes coloniaux : l'essai a été tenté sur deux bryozoaires crétacés libres, Stichopora pentasticha et Lunulites mitra. En dépit de différences marquées dans le mode de vie, les espèces analysées montrent des structures de populations très proches de celles de la plupart des invertébrés solitaires et benthiques, c'est-à-dire que les espèces analysées sont sujettes à une mortalité juvénile élevée diminuant probablement avec la maturité. D'autre part, le moment de maturité sexuelle diffère dans les deux espèces reflétant sans doute leurs habitudes différentes. Puisqu'aucune façon de déterminer la relation âge absolu-taille n'a été trouvée, il n'est pas possible de construire la courbe de survivance. Néanmoins, l'observation attentive des distributions taille-fréquence en relation avec les inférences morphologiques fonctionnelles assure une information importante quant aux variations des pourcentages de croissance et de mortalité liés au développement ontogénique.Hakansson Eckart. Population structure of colonial organisms. A palaeoecological study of some free-living cretaceous bryozoans. In: Documents des Laboratoires de Géologie de la Faculté des Sciences de Lyon. Hors série n°3, 1975. Bryozoa 1974 – Proceedings of the third Conference International Bryozoology Association – Lyon (fasc. 2) pp. 385-400

The Cretaceous-Palaeogene boundary succession at Stevns Klint, Denmark : foraminifers and stable isotope stratigraphy

The Cretaceous–Palaeogene boundary exposed at Stevns Klint (Denmark) provides an important location for the investigation of the end-Cretaceous event. In this work we have used a number of sections across the boundary, including the little described, expanded stratigraphic sequence at Kulstirenden which is located 7 km north of Højerup (where most published work is derived). Using stratigraphical, micropalaeontological and stable isotope (δ18O and δ13C) data we have shown that there is clear evidence of shallowing in the latest Maastrichtian. Prior to, and across, the Cretaceous–Palaeogene boundary there are significant changes in sea water temperature, including an important cooling event in the very latest Maastrichtian. The δ13C record in the expanded boundary clay (Fish Clay) sequence at Kulstirenden indicates a number of significant excursions of decreasing magnitude up-section. The evidence from the distribution of the foraminifers has been incorporated with previous work to develop a sequence stratigraphical interpretation for the succession that can be compared to other Cretaceous–Palaeogene boundary successions in Europe