Material and Methods

Several well-preserved phragmocones from the Upper Callovian (- lamberti -zone) of Dubki near Saratov, Russia (provided by Dr. V. Mitta) were investigated (for the stratigraphy of Dubki, see Keupp and Mitta, 2004).

Our phragmocones might be easily assigned to Belemnotheutis polonica Makowski, 1952, which occurs in the - lamberti - zone of Lukow (Poland). But as there are no distinctive characters for a morphological differentiation between our specimens and the type material of B. antiquus Pearce, 1847 (Donovan and Crane, 1992; Doyle and Shakides, 2004) from the Callovian (- athleta - zone) of Christian Malford, England, we consider these taxa in synonymy.

Six uncrushed specimens (MC-1-MC-6) are between 22-31mm in maximum length and 12-22 mm in maximum diameter (Fig. 14.2). The cross section is almost circular. The apical angle is always 20┬░. The earliest chambers including the protoconch are not preserved. Another dorsoventrally flattened specimen (MC-7), which is 100 mm in maximum length, might be considered as fully grown. In the same specimen the most apical part of the rostrum is preserved but the earliest camerae including the conotheca are replaced by pyrite. None of the studied specimens retains a proostracum in situ.

Table 1. Comparison of previous ultrastructural observations on belemnoid conotheca.

Sequence of layers

Table 1. Comparison of previous ultrastructural observations on belemnoid conotheca.

Sequence of layers

Order Authors

External

Intermediate

Investigated

Ontogenetic taxa

Investigated stage

plane

Christensen, 1925

Prismatic

-

Prismatic

Megateuthis

embryonic

?

(= primordial

rostrum?)

Muller-Stoll, 1936

Thick Prismatic

Thin organic

Thin prismatic

Chitinoteuthis

embryonic

?

(=primordial

rostrum?)

Mutvei 1964 (p. 97)

Periostracum?

Nacreous

Thin prismatic

Megateuthis

?

longitudinal?

Jeletzky 1966

Thick Prismatic

Very thin,

Thick prismatic

Megateuthis

Embryonic

Medial (ventral)

(p. 124)

(Primordial

mineralized

rostrum?)

Barskov, 1972

-

Nacreous

Prismatic

Conobelus,

Embryonic

?

Pachyteuthis,

Mesohibolithes

Hewitt and Pinkney,

?

Thick nacreous

Thin prismatic

Acroteuthis

Juvenile-adult

Transversal

1982 (p. 144)

(dorsal?)

Bandel et al., 1984

Primordial

Organic

Thin prismatic

Hibolithes

Embryonic-

(p. 276, 285)

rostrum

postembryonic

Medial

Bandel and Kulicki,

Thin Prismatic

Nacreous

Thin prismatic

Belemnotheutis

Adult?

?

1988 (p. 310)

Megateuthis

Doguzhaeva et al.,

Primordial

Nacreous

-

Conobelus

Embryonic-

Medial

1999 (p. 255)

rostrum

postembryonic

Doguzhaeva et al.

Thin proostracal

Nacreous

Prismatic

Megateuthis

Adult

Longitudinal

2002 (p. 324)

layers

(dorsal)

Doguzhaeva et al.

Primordial

Thin proostracal

Prismatic

Passalotheutis?

Embryonic-

Medial + Transversal

2003b (p. 83)

rostrum

layers

postembryonic

(dorsal + ventral)

Aulaco-cerida

Hematitida

Phragmo-teuthida

Dauphin. 1983 Bandel. 1985

(p. 233) Cuif and Dauphin. 1979

Doguzhaeva et al.. 2002 Doguzhaeva et al..

2002.2003a Doguzhaeva et al.. 2003a (p. 67)

Periostracum

Lamellar Thin Nacreous prismatic Organic Nacreous

Prismatic Prismatic

Prismatic

Nacreous prismatic 5-6 prismatic layers without nacre?

Irregulary mineralised

Proostracal layers

Lamello- Prismatic fibrillar

Aulacoceras Dictyoconites

Atractites

Mutveiconites

Hematites

Adult ?

Juvenile ?

Postembiyonic ?

Donovaniconus Juvenile-adult Medial (dorsal?)

The thin sheath-like rostrum surrounding the phragmocone has a brownish color. X-ray diffraction analyses revealed that it is typically composed of aragonite. On the mid-dorsal line of the rostrum, characteristic rounded ridges (Fig. 14.2) are present. As demonstrated by Makowski (1952), they run parallel in the earliest ontogenetic stages but diverge at later stages until they disappear at a phragmocone diameter of approximately 18 mm. Specimen MC-7 demonstrates that the dorsal ridges are already developed at the earliest ontogenetic stages.

Conotheca and septal sutures are visible where the thin rostrum has flaked off. When this is the case in the dorsolateral region, a sharp and colored separation is evident on the outer conothecal surface (Fig. 14.2). Toward the dorsum, the surface is black. Weak imprints of proostracal growth lines are visible. They are similar to those described by Doguzhaeva et al. (2002) in Megateuthis. Toward the venter, the surface exhibits an iridescence that takes up two-thirds of the ventral phragmocone circumference.

Two specimens selected for ultrastructural studies (MC-8, MC-9) were fractured. Cross and longitudinal fractures were produced between a phragmocone diameter of 4 mm and 10 mm. This region corresponds presumably to the 10th-36th camera, i.e., juvenile, adolescent, and presumably adult stages.

Opened camerae were completely filled with sediment. Due to diagenetic dissolution, the septal and siphonal morphology of Belemnotheutis could not be investigated.

Shell fractures were only cleaned, coated with gold, and studied with SEM. All specimens (MC-1-MC-9) are stored in the Institute of Geological Sciences, Paleontology, Freie Universit├Ąt Berlin.

Fig. 14.2 Belemnotheutis antiquus (=polonica). Dorsal view of specimen MC-5. The paired ridges are visible. Where the rostrum (ro) is flaked off on the dorsolateral part, an abrupt change in color is visible (arrows).

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