Geology Reference
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Fig. 10.45. Accumulations of belemnite rostra (predominantly Dactyloteuthis ) on a marly-calcareous bedding surface accu-
rately named 'belemnite battlefield'. The bed overlies the black organic-rich Posidonia shales, interpreted as deposition in
dysaerobic-anaerobic basins with fluctuating oxygen conditions at the sediment-water interface. Early Jurassic (boundary
Early/Late Toarcian): Mistelgau, southwest of Bayreuth, northern Franconian Alb, Germany. Large specimens up to 10 cm
long. Courtesy of C. Schulbert (Erlangen).
environments of Palaeozoic cephalopod limestones. -
Sedimentary Geology, 44 , 263-300
Zapfe, H. (1963): Aptychenlumachellen. - Annalen des Natur-
historischen Museums Wien, 66 , 261-266
Further reading: K124
ings (annular rings) and fine concentric or longitudinal
striations.
Longitudinal sections show narrow V-shaped figures
(apical angle up to 20°); in cross sections circular, el-
liptical or polyhedral figures can be observed. Excel-
lent thin-section microphotographs can be found in
Farsan (1994). Tentaculites may be confused with bra-
chiopod spines (see Pl. 86/6).
10.2.4.5 Tentaculitids and Other Conical Shells
(Cricoconarida; Hyolithida)
The class includes two orders - the Tentaculitida and
the Dacryconarida. The tentaculitids (Ordovician to
Late Devonian II) have concentric ring-like thicken-
ings at the exterior surface but a smooth interior wall
surface. The shells (length commonly 15-30 mm) are
pointed, the initial part is chambered. The microstruc-
ture is finely laminated and can have fine perforations
near the apertura. The dacryconarids (Ordovician to
Late Devonian II), comprising the nowakiids and
styliolinids, are characterized by small shells, apical
angles larger than in tentaculitids, a bubble-shaped and
unchambered initial shell section, and smooth or lon-
gitudinally striated, shell surfaces.
This group comprises the styliolinids and nowakiids,
the latter characterized by ringed exterior and interior
surfaces. The s tyliolinids have smooth exterior and in-
terior shell surfaces. Styliolina differs from Tentacu-
Tentaculitids are extinct millimeter- to a few centi-
meter-sized exclusively Paleozoic fossils of uncertain
affinities but now considered as a class of the Mollusca.
They are characterized by slender conical calcitic shells
occurring in rock-building abundance in Ordovician to
Late Devonian open-marine and basinal carbonates.
Tentaculitids and related fossils are common constitu-
ents of Devonian pelagic and hemipelagic limestones.
Morphology and classification: The conical shells
have a pointed apex, some groups are chambered. Clas-
sification is based on the shell sculpture, type and angle
of the apex and shell microstructure. The class Crico-
conarida is defined by having conical calcareous shells
with ringlike exterior sculptures. The exterior of the
shell is characterized by periodic concentric thicken-
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