Fossilized Soft Tissue Remnants Chemical Composition

In spite of significant ultrastructural differences between the fossilized soft tissues and the sediment around the shell (Fig. 6.7A-E), the EDAX analysis did not reveal noticeable differences in their chemical composition with the exception of a slightly higher content of Si in the former. Both contain O, Si, Fe, C, Mg, and Ca, but have no P.

3.3.2 Muscular Mantle

Studies with SEM show that the material collected from the shell surface (Figs. 6.6, 6.7A) is porous and contains diverse microorganisms. It includes debris of plastically deformed (folded or rolled) material (Fig. 6.9). At higher magnifications (x 10,000 to x 20,000), the material is seen to consist of numerous superimposed, sheets of irregular thickness. On the surface, these sheets are disrupted in numerous places and give the impression that they were exposed to strong tension during fos-silization. The sheets exhibit distinct, parallel fibers about 0.1|im in diameter (Fig. 6.9B). The fibers have a fine granular ultrastructure, and they are arranged into bundles (Fig. 6.10A). The latter indicates that the sheets under examination represent a fossilized muscular mantle.

In some aspects, the mantle tissue of the Mazon Creek specimen is similar to the fossilized mantle in the Upper Triassic ceratitid Austrotrachyceras (Doguzhaeva et al., 2004c), but in other aspects it is also similar to the mantle in the Late Jurassic Belemnoteuthis (Owen, 1844) and the Early Jurassic squid-like coleoid Loligosepia (Kear et al., 1995; Doguzhaeva and Mutvei, 2003). The mantle in the ceratitid Austrotrachyceras (Fig. 6.11A) also has a sheet-like pattern (Doguzhaeva et al., 2004c: Fig. 6.4A) with a fine lamination and a fibrous ultrastructure (Doguzhaeva et al., 2004c: Fig. 6.2A, B), but it does not have the fibers arranged into bundles as in the squid-like Loligosepia (Doguzhaeva et al., 2004c: Fig. 6.6A, B). However the mantle in the Mazon Creek specimen has no distinct transverse striations formed by alternation of circular, longitudinal, and transverse muscle fibers. Therefore, the level of development of the mantle structure in the Mazon Creek specimen seems to have been somewhere between that in the less muscular mantle in ceratitid Austrotrachyceras and those seen with a more advanced mantle structure such as those in the squid-like coleoid Loligosepia.

In spite of a different chemical substitution during fossilization (phosphatized in soft-bodied squids from the Jurassic Oxford Clay, England (Allison, 1988), and Loligosepia from the Posidonian Schiefer, Holzmaden, Germany, bituminous in Austrotrachyceras from the Reihgraben Shales, Schindelberg locality, Lower Austria, and rich in Si in the specimen from the Mazon Creek area, Illinois, USA), the mantle in specimens of all taxa shows a granular ultrastructure. This was probably caused by different bacteria that caused the precipitation of different elements (in the Posidonian Schiefer by P-accumulating bacteria, in the Reihgraben Shales by C-accumulating bacteria, and in the Mazon Creek area by Si-accumulating bacteria).

3.3.3 Ink Substance

The substance that is interpreted to be dispersed ink (Fig. 6.7C) consists of a mass of tiny, globular granules, 0.1-0.4 |im in diameter. Each granule is an agglomerate of

Fig. 6.9A, B. Saundersites illinoisiensis g. and sp. n., PE32521. A. Fragment of fossilized muscular mantle among debris of soft tissues. B. Fibrous ultrastructure of the muscular mantle; the fibers form a criss-cross pattern, enlarged view of Fig. A. Each division of the scale bar in A is 1.2 flm and in B is 0.12mm.

Fig. 6.9A, B. Saundersites illinoisiensis g. and sp. n., PE32521. A. Fragment of fossilized muscular mantle among debris of soft tissues. B. Fibrous ultrastructure of the muscular mantle; the fibers form a criss-cross pattern, enlarged view of Fig. A. Each division of the scale bar in A is 1.2 flm and in B is 0.12mm.

smaller particles (Fig. 6.7E). These granules do not form layers or fibers as do the granules in fossilized soft-tissues, and they are ultrastructurally identical to the ink in present-day and fossil coleoids (Fig. 6.11B-D). The matrix of the concretion around the specimen has crystal-shaped grains (Fig. 6.7B, D) indicating its abiotic origin.

Fig. 6.10A Saundersites illinoisiensis g. and sp. n, PE 32521. Fragment of fossilized muscular mantle. Each division of scale bar is 0.6flm. B. Austrotrachyceras sp., NHMW2005z/0006/0001, Upper Triassic, Lower Carnian, Lower Austria, locality Schindelberg near Lunz. Fragment of fossilized muscular mantle. Each division of the scale bar is 3flm.

Fig. 6.10A Saundersites illinoisiensis g. and sp. n, PE 32521. Fragment of fossilized muscular mantle. Each division of scale bar is 0.6flm. B. Austrotrachyceras sp., NHMW2005z/0006/0001, Upper Triassic, Lower Carnian, Lower Austria, locality Schindelberg near Lunz. Fragment of fossilized muscular mantle. Each division of the scale bar is 3flm.

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