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Fig. 10.38. Preservation of rugose corals compared with that of scleractinian corals. A: Late Permian rugose coral from
Oman. All the diagnostic skeletal elements (septa, dissepiments, axial structure, external wall) are well preserved. B: Late
Jurassic scleractinian coral from the Northern Calcareous Alps. Diagnostically important skeletal elements are only partly
preserved. The thickness and shape of the septa are moderately modified by diagenesis, but the center and the periphery of
the corallites are strongly affected. Scale is 2 mm.
environments and are susceptible to dissolution and
neomorphism under burial or subaerial conditions. Dis-
solved skeletal elements may be preserved as spar-filled
or sediment-filled molds. Identification of scleractin-
ian corals requires recognizing the microstructures of
calices and septa, but these fine structures are often de-
stroyed by diagenesis. Sometimes weak neomorphism
of coral skeletons can lead to the preservation of the
internal microstructures. Common diagenetic modifi-
cations of scleractinian coral skeletons include the thick-
ening of skeletal elements and the formation of pseudo-
skeletal elements.
Rugose corals apparently secreted a calcitic skel-
eton and are therefore not as strongly affected by dia-
genetic modifications as scleractinians (Pl. 29/2; Fig.
10.38).
schungsinstitut Senckenberg, 164 , 63-70
Veron, J.E.N. (1995): Corals in space and time. The biogeo-
graphy and evolution of the Scleractinia. - 321 pp., Sidney
(UNSW Press)
Wells, J.W. (1956): Scleractinia. - Treatise on Invertebrate
Paleontology, F, Coelenterata. - 328-440, Lawrence (Geo-
logical Society of America)
Further reading: K119, K120, K121
10.2.3.4 Bryozoans
Bryozoan carbonates reflect specific depositional set-
tings and paleoclimatic conditions. Bryozoans are pre-
dominantly marine, active suspension feeders forming
millimeter- to a several centimeter-sized colonies oc-
curring from tidal level down to bathyal depths. They
dominate in shelf seas, are abundant in depths between
the intertidal zone and about 80 m and live both in low
and high latitudes.
Coral structures in thin sections: Plate 83 and 84 show
some of the characteristic features of rugose and tabu-
late corals, heterocorals and scleractinians seen in thin
sections.
Morphology: The colony (zoarium) consists of inter-
connected individuals (zooids) usually living within
calcareous tube- or boxlike chambers (zooecia) that may
or may not exhibit a number of transverse plates. An
opening (apertura) is developed at one end of the zooecia.
Zooecia and apertures exhibit strong polymorphism re-
flecting different vital functions of zooids. The colo-
nies have wide ranges in form and size. They may be
massive, encrusting, stick-like or correspond to a deli-
cate branching network. The taxonomic differentiation
of bryozoans requires thin-section studies.
The skeleton of modern marine bryozoans consists
of Low-Mg calcite or intermediate-Mg calcite (Cyclo-
Basics: Corals
Hill, D. (1981): Rugosa and Tabulata. - Treatise on Inverte-
brate Paleontology, Coelenterata, supplement 1. - 762 pp.,
Lawrence (Geological Society of America)
Oliver, W.A., Coates, A.G. (1987): Phylum Cnidaria. - In:
Boardman, R.S., Cheetham, A.H., Rowell, A.J. (eds.):
Fossil invertebrates. - 140-193, Palo Alto (Blackwell)
Schuhmacher, H., Zibrowius, H. (1985): What is her-
matypic? A redefinition of ecological groups in corals and
other organisms. - Coral Reefs, 4 , 1-9
Scrutton, C. (1999): Palaeozoic corals: their evolution and
palaeoecology. - Geology Today, 15 , 184-193
Sorauf, J.E. (1993): The coral skeleton: analogy and com-
parisons. Scleractinia, Rugosa and Tabulata. - Courier For-
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