The Black Bituminous Substance in the Body Chamber

The black, bituminous substance in the body chamber (Fig. 11.1A, C-E) looks like shiny pitch that has solidified after being squeezed between the crushed shell walls of the body chamber. The black substance (1) is missing in the chambers of the phrag-mocone, (2) is only present orad of the last septum, (3) has a somewhat variable thickness and extent, and (4) is restricted to the body chamber and is not present in the surrounding sediment. The black substance is best exposed where the wall of the body chamber is removed when the enclosing shale is split. The black material separates easily from the underlying shell wall and is lighter than the shell material.

Fig. 11.1A-E Austrotrachyceras sp. A-C. NHMW 2005z/0006/0006. D,E. NHMW2005z/0006/ 0001. A. Shell and mandibles near the aperture. Black material in the shell is exposed where the body chamber shell wall has been removed. x 1.5. B. Enlarged view of the upper and lower mandibles; the lower mandible is poorly exposed around the periphery of the upper mandible. x 5.5 C. Enlarged view of a fragment of the black material in the body chamber. x 5.2, D, E. Lateral view of the compressed shell with black material squeezed in the body chamber and exposed in its middle part where the shell wall is removed. x 1.0. E. Enlarged view of the black material showing its pitch-like appearance. x 3.5.

Fig. 11.1A-E Austrotrachyceras sp. A-C. NHMW 2005z/0006/0006. D,E. NHMW2005z/0006/ 0001. A. Shell and mandibles near the aperture. Black material in the shell is exposed where the body chamber shell wall has been removed. x 1.5. B. Enlarged view of the upper and lower mandibles; the lower mandible is poorly exposed around the periphery of the upper mandible. x 5.5 C. Enlarged view of a fragment of the black material in the body chamber. x 5.2, D, E. Lateral view of the compressed shell with black material squeezed in the body chamber and exposed in its middle part where the shell wall is removed. x 1.0. E. Enlarged view of the black material showing its pitch-like appearance. x 3.5.

The SEM study shows that the black substance forms two sheets that are indistinctly separated by an uneven interspace (Fig. 11.4A, B). These sheets are laminated (Figs. 11.2A, C, 4C), and the laminae are often broken into irregular plates and patches (Figs. 11.4E, F, 6C). Due to differences in preservation, the sheets have a varying ultrastructure: a granular porous ultrastructure (Fig. 11.3B, C), a globular ultrastructure consisting either of irregularly sized globules (Fig. 11.6A) or regularly sized globules (Fig. 11.5C), or an irregular rodlike interconnected ultrastructure (Fig. 11.5D-F). In places, the laminae show a fibrous ultrastructure with the fibers consisting of numerous globules (Figs. 11.2C, 3A) or granules (Figs. 11.4E, F, 6C; see also Doguzhaeva et al., 2004b: Fig. 11.2A). The interspace between the two sheets contain debris that was probably originally organic material and organ pieces, which has been plastically deformed and sometimes folded (Fig. 11.4D). The outer surface of the sheets facing the wall of the body chamber shows a regular honeycomb-like pattern (Doguzhaeva et al., 2004b: Fig. 11.3A-C) with cells the size of which corresponds to that of nacreous tablets of the shell wall (ca. 0.3 |im). The microlamination of the two sheets of black substance, and the fibrous structure of each lamina (Fig. 11.3A), indicate that the sheets were originally a muscular tissue.

The SEM observations on the dispersed material preserved within the interspace between the two sheets of black substance reveal agglomerations of tiny globules (diameter is ca. 0.1-0.4 |im) each of which consists of smaller particles (Fig. 11.6A, B). The globules lack laminations, fibrous patterns, or any other structure. This material with a globular ultrastructure between both sheets of the black substance is comparable to described occurrences of fossil and modern coleoid ink (Doguzhaeva et al., 2002, 2003, 2004a). This globular ultrastructure of the ink in cephalopods has been demonstrated in Loligo and in several other undetermined living squids, sepiids, and octopuses and in the fossil ink of Carboniferous, Jurassic, and Cretaceous coleoids (Doguzhaeva et al., 2002; Doguzhaeva and Mutvei, 2003; Doguzhaeva et al., 2003, 2004a). The solidified ink seems to be the result of rapid coagulation of the melanin particles (the main constituent of ink) during precipitation. The ink solidification requires an acid or neutral environment (Fox, 1966). Such a pH environment could be produced by either bacterial decomposition activity on the dead animal or by chemical alteration of the ocean water at the water/sediment interface by bacterial activity or both.

The ultrastructure of the black material in the body chamber was compared to the muscle tissue of the buccal mass in a specimen of the modern squid Loligo, which was air dried for one year, and in a specimen of Nautilus muscle mantle tissue, which was preserved in alcohol for 20 years. The muscle tissue in the buccal mass of the modern squid shows that a globular ultrastructure similar to the globular ultrastructure seen in the black material had formed. The longitudinal muscles have an almost smooth appearance with a fine granular surface, whereas the transverse muscles have a more robust globular size (Fig.11.7C-D). In Nautilus, the muscular mantle tissue is well preserved and has a globular ultrastructure (Fig. 11.7E, F).

The black substance that forms two sheets in the body chamber in Austrotrachyceras was compared by SEM with isolated blobs of black substances in the shale that surround the ammonoid shells. These blobs lack a fibrous, globular, or laminar ultrastructure, and thus, they are not related to the black material in the body chambers of the ammonoids.

EDS analysis on one specimen demonstrates that the black substance has the following chemical composition in percents of the total weight: C (60-65%); O (30%); S (2-6%); Si (1-2%); Cd (0.5-1.8%); Fe and K (1%), Al and Zn (each less than 1%) (Doguzhaeva et al., 2004b). The lack of significant amounts of iron

Fig. 11.2A-C Austrotrachyceras sp. A, B. NHMW2005z/0006/0002. C. NHMW2005z/0006/0003.

A. Fracture of the shell showing the squeezed black material (bottom) in compressed body chamber (top). The lamination in the middle of the black material is supposed to represent the contact between the left and right sides of (he fossilized mantle preserved in (he squeezed body chamber Scale bar = 60¡¡m.

B. Enlargement of (he body chamber shell wall composed mostly of (he nacreous layer. Scale bar = 10jm;

C. Enlarged view of A showing (he microlaminations in (he black material. Scale bar = 1.2¡¡m.

Fig. 11.2A-C Austrotrachyceras sp. A, B. NHMW2005z/0006/0002. C. NHMW2005z/0006/0003.

A. Fracture of the shell showing the squeezed black material (bottom) in compressed body chamber (top). The lamination in the middle of the black material is supposed to represent the contact between the left and right sides of (he fossilized mantle preserved in (he squeezed body chamber Scale bar = 60¡¡m.

B. Enlargement of (he body chamber shell wall composed mostly of (he nacreous layer. Scale bar = 10jm;

C. Enlarged view of A showing (he microlaminations in (he black material. Scale bar = 1.2¡¡m.

Fig. 11.3A-C Austrotrachyceras sp, NHMW 2005z/0006/0004. A. Surface view of the black material (supposed fossilized mantle) showing microfractures possibly parallel to the muscle fibers. Scale bar = 3pm. B. Piece of the mantle tissue showing porous surface. Scale bar = 12.0pm. C. Enlarged view of B to show tubes perforated by pores. Scale bar = 3.0 pm.

Fig. 11.3A-C Austrotrachyceras sp, NHMW 2005z/0006/0004. A. Surface view of the black material (supposed fossilized mantle) showing microfractures possibly parallel to the muscle fibers. Scale bar = 3pm. B. Piece of the mantle tissue showing porous surface. Scale bar = 12.0pm. C. Enlarged view of B to show tubes perforated by pores. Scale bar = 3.0 pm.

Fig. 11.4A-F Austrotrachyceras sp, NHMW2005z/0006/0001. A. Fragment of the black material from the body chamber showing its surface and fractures. Scale bar = 60.0pm. B. Enlargement of A to show that the black material consists of the left and right portions separated by an interspace about midway between them. The interspace contains possible soft tissue debris. Scale bar = 30.0mm.

C. Fractured surface of the black material to show longitudinal microlamination. Scale bar = 1.2pm.

D. Irregularly shaped swollen structures on the surface of the black material supposed to be deformed soft tissue debris. Scale bar = 1.5pm. E. Fragment of the black material (supposed fossilized mantle) to show that it was fractured into small broken pieces giving an impression of being originally composed of plastic organic material. Scale bar = 6.0p.m. F. Fractured and irregular plates as seen in E above. The plates have a granular surface. Scale bar = 1.2pm.

Fig. 11.4A-F Austrotrachyceras sp, NHMW2005z/0006/0001. A. Fragment of the black material from the body chamber showing its surface and fractures. Scale bar = 60.0pm. B. Enlargement of A to show that the black material consists of the left and right portions separated by an interspace about midway between them. The interspace contains possible soft tissue debris. Scale bar = 30.0mm.

C. Fractured surface of the black material to show longitudinal microlamination. Scale bar = 1.2pm.

D. Irregularly shaped swollen structures on the surface of the black material supposed to be deformed soft tissue debris. Scale bar = 1.5pm. E. Fragment of the black material (supposed fossilized mantle) to show that it was fractured into small broken pieces giving an impression of being originally composed of plastic organic material. Scale bar = 6.0p.m. F. Fractured and irregular plates as seen in E above. The plates have a granular surface. Scale bar = 1.2pm.

Fig. 11.5A-F Austrotrachyceras sp., NHMW2005z/0006/0009. A. Surface view on the exposed black material with the underlying shell wall of the body chamber bearing tubercles. Scale bar = 1.2 jm. B. Enlarged view of the black material coating the inner surface of the tubercle and forming the circular outline around its base. Scale bar = 0.3 mm. C. Porous globular ultrastructure of the black material on the conical surface of the tubercle. Scale bar = 6.0 jm. D. Enlargement of B to show the ultrastructural differences between the black material infilling the tubercle and lining the rest of the inner surface of the body chamber The lighter material at the base of the photograph has a spherical ball-like globular structure while the upper darkened material has an irregular rodlike interconnected structure. Scale bar = 12.0 jm. E. Close up of the interconnected rodlike structures seen in D. Scale bar =6.0 jm. F. Detailed enlargement showing parts of the irregular rodlike structures and their granular ultrastructure. Scale bar = 1.5jm.

Fig. 11.5A-F Austrotrachyceras sp., NHMW2005z/0006/0009. A. Surface view on the exposed black material with the underlying shell wall of the body chamber bearing tubercles. Scale bar = 1.2 jm. B. Enlarged view of the black material coating the inner surface of the tubercle and forming the circular outline around its base. Scale bar = 0.3 mm. C. Porous globular ultrastructure of the black material on the conical surface of the tubercle. Scale bar = 6.0 jm. D. Enlargement of B to show the ultrastructural differences between the black material infilling the tubercle and lining the rest of the inner surface of the body chamber The lighter material at the base of the photograph has a spherical ball-like globular structure while the upper darkened material has an irregular rodlike interconnected structure. Scale bar = 12.0 jm. E. Close up of the interconnected rodlike structures seen in D. Scale bar =6.0 jm. F. Detailed enlargement showing parts of the irregular rodlike structures and their granular ultrastructure. Scale bar = 1.5jm.

Fig. 11.6A-C Austrotrachyceras sp. A. NHMW 2005z/0006/0002. View of the fractured black material in places where it consists of larger and smaller irregularly shaped and sized globular particles (supposed to be a mixture of organic debris preserved on the inner surface of the mantie). Scale bar = 3.0ßm. B. NHMW2005z/0006/0001. View ofthe fractured black material in places where it consists of dispersed globules (central and left parts ofthe photo) that are similar in shape to described fossil and Recent ink of coleoids (also supposed to be an ink). Scale bar = 1.2 mm. C. Enlarged detail of Fig. 11.4E to show the granular ultrastructure of the fractured pieces of black material (supposed mantle). Scale bar = 3.0ßm.

Fig. 11.6A-C Austrotrachyceras sp. A. NHMW 2005z/0006/0002. View of the fractured black material in places where it consists of larger and smaller irregularly shaped and sized globular particles (supposed to be a mixture of organic debris preserved on the inner surface of the mantie). Scale bar = 3.0ßm. B. NHMW2005z/0006/0001. View ofthe fractured black material in places where it consists of dispersed globules (central and left parts ofthe photo) that are similar in shape to described fossil and Recent ink of coleoids (also supposed to be an ink). Scale bar = 1.2 mm. C. Enlarged detail of Fig. 11.4E to show the granular ultrastructure of the fractured pieces of black material (supposed mantle). Scale bar = 3.0ßm.

Fig. 11.7A-D Modern squid (Loligo) after one year drying. A. Fracture of the buccal mass showing mandible and muscle preservation. Scale bar = 0.6 mm. B. Fibrous pattern of the buccal mass muscle seen in A, above. Scale bar = 30.0 jm. C. Enlarged view of B to show alternation of longitudinal and transverse muscle. Scale bar = 6.0p.m. D. Enlargement of C showing the transverse muscles with a globular surface bordered by longitudinal muscles with an almost smooth appearance consisting of smaller and less pronounced grains. Scale bar = 1.2 jm. E, F Recent Nautilus after 20 years in 95% ethyl alcohol. Fibrous pattern of the muscular mantle. Scale bar = 120 jm. F. Enlarged view of the muscular mantle showing the interconnected globular ultrastructure with each globule having a granular surface. Scale bar = 12.0 jm.

Fig. 11.7A-D Modern squid (Loligo) after one year drying. A. Fracture of the buccal mass showing mandible and muscle preservation. Scale bar = 0.6 mm. B. Fibrous pattern of the buccal mass muscle seen in A, above. Scale bar = 30.0 jm. C. Enlarged view of B to show alternation of longitudinal and transverse muscle. Scale bar = 6.0p.m. D. Enlargement of C showing the transverse muscles with a globular surface bordered by longitudinal muscles with an almost smooth appearance consisting of smaller and less pronounced grains. Scale bar = 1.2 jm. E, F Recent Nautilus after 20 years in 95% ethyl alcohol. Fibrous pattern of the muscular mantle. Scale bar = 120 jm. F. Enlarged view of the muscular mantle showing the interconnected globular ultrastructure with each globule having a granular surface. Scale bar = 12.0 jm.

and calcium indicates that neither pyrite nor calcite is of importance as preservational elements in this substance. Even more significant is the lack of phosphorus. Many soft tissues in fossil coleoids are commonly replaced by phosphorus in the form of apatite. The lack of this element indicates that the preservation of the muscular mantle tissue and possible ink is not controlled by a phosphorus rich medium.

To summarize, the black substance (1) is restricted to the body chamber and is absent in the chambers of the phragmocone, (2) consists of the left and right sheets that are almost fused but separated by an indistinct interspace containing dispersed organic material, (3) exhibits in places both fine laminations, (4) a fibrous ultrastructure in each lamina, and (5) consists predominantly of carbon. The interspace between the two sheets of the black substance contains isolated agglomerations of tiny globules (ca. 0.1-0.4 |im in diameter); each globule consists of smaller particles. The globule agglomerations lack laminations, fibrous patterns, or any other discernable organized arrangement and are interpreted to be fossil ink. The fine laminations and fibrous ultrastructure of the black sheets, in combination with the high carbon content, are known to be the principal characters of fossilized muscular mantle material. The morphological, ultrastructural, and chemical features listed above allow the interpretation that the sheets of black substance are the bituminous remnants of the mantle squeezed within the compressed body chamber so that their left and right sides became nearly fused during compaction. Due to the fusion of the two portions of the mantle, the dispersed fragments of soft body tissues and organs seem to be partly preserved in the interspace between the sheets. It is likely that the ink sac was ruptured, and ink was dispersed throughout the body cavity and into the mantle tissues. This would explain the dispersed nature of the isolated agglomerations of tiny globules, which are typical of the ultrastructure of ink in other fossil and modern cephalopods. Our observations and conclusions are based on a limited number of specimens. The possible occurrence of ink in ammonoids is an important paleo-biological discovery with many implications for the life mode and biology of this extinct group of animals. Previous suggestions that ammonoids had ink have been rejected as inconclusive. However, based on the ultrastructural evidence presented above, we suggest with reservations that it is possible that some ammo-noids may have had ink and that it was used as a defensive mechanism. Thus, Lehmann's (1967) report of the occurrence of ink in some ammonoids should not be rejected, and additional specimens should be sought to confirm or reject this possibility in at least some ammonoids.

The replacement of the soft tissues in Austrotrachyceras by carbon is probably the result of the metabolism of carbon-accumulating anaerobic bacteria that replaced the organic fibers in the mantle by the globular granules of carbon during the slow fiber decay. The case for slow decay can be supported since the bottom environment in the sediment at and below the sediment/water interface at that time is assumed to be of low oxygen content (Griffith, 1977), and if this was the case, anaerobic bacteria would have been the dominant biological breakdown agent. Additionally, the removal of other chemical constituents other than carbon was probably promoted by liquefying the body tissues and organs by bacterial action, hydrostatic and lithostatic pressures with pore fluid movement, and chemical r eactions within the mud surrounding the ammonoid body and shell during diagenesis.

The depositional environment of the Lower Carnian Trachyceras Shale in the Lower Austrian Alps and that of the Posidonia Shale at Holzmaden (both have yielded numerous coleoids with preserved soft parts) was previously believed to have been similar (Seilacher, 1982). However, the EDS analysis of the soft tissues of the cepha-lopods from both localities does not completely support this depositional environmental interpretation (Doguzhaeva et al., 2004b). In contrast to the carbon-dominated preservation of the soft tissues in the ammonoid Austrotrachyceras from the Trachyceras Shale, the soft tissues in the coleoids preserved in the Holzmaden Shale are replaced by phosphorus in the form of phosphate minerals. The geochemical conditions that supported soft tissue preservation by carbon coating and/or carbon concentration by distillization versus phosphate replacement and/or coating have not been precisely determined. However, even though both environments are interpreted to have been a low oxygen environment, the pH of the sediment and pore water in which the dead cephalopods were encased was probably very different in the two shales.

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