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Keywords:

  • Annelida;
  • polychaete;
  • parasitism;
  • calcified tissue;
  • paleopathology

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. References

A putative calcified soft tissue or parasite recovered in the pelvis of an adult male Late Roman burial from Aqaba, Jordan, is a fossil marine invertebrate. Copyright © 2011 John Wiley & Sons, Ltd.

In their meticulous case study of a putative soft tissue calcification from the pelvic region of an adult male, Perry et al. (2008) neglect a critical first step in the identification of the calcified object they describe. They have failed to ask whether the object is correctly identified as a human body part.

Although we depend on their excellent photographs and radiographs and have not examined the object in the flesh, so to speak, we are confident that it is a calcified marine worm casting. Polychaete worms construct complexes of cylindrical tubes of mucus-cemented debris. The tubes may be excavated in sediment or incrusted on hard substrates, depending on the species. When the animals die, their tubes can fill with sediment or with crystalline or amorphous mineral deposits. Fossils of this kind are found in deposits from the Early Paleozoic to Recent, and they are fairly common (Fauchald & Jumar, 1979).

Illustrations of comparable fossils are widely available. Mark Wilson's image of a Pliocene serpulid polychaete from Cyprus is a particularly good match for the Aqaba fossil (Wilson, 2011). Figures 3 and 4 of Seilacher et al. (2008) describe Glomerula plexus, a soft-bottom worm tube having the appearance of the specimen described. G. plexus can form large colonial complexes of ‘spaghetti-form’ individuals or be solitary and raised above a soft marine substrate. Worm castings are trace fossils, meaning that they are produced by the organism, but the organism itself is not necessarily preserved. Polychaete castings are so common that they have been given their own taxonomic nomen, Lapispectus cunniculus (Teichert, 1970), the species name being the Latin word for burrow. Polychaeta is a class of marine worms of enormous diversity. The proper taxonomy of polychaetes depends on their appendages and jaws (Eriksson et al., 2000; Merz & Woodin, 2006), and we will not attempt a more detailed identification here.

Perry and colleagues note that their object is densely mineralised and that it lacks internal histological structure. They find that does not correspond to any of the calcified soft tissues in the literature they review, and they suggest that it ‘represents the remains of a calcified parasite of an unknown species’ (Perry et al., 2008:516). Their observations are consistent with the identification of this object as a fossilised cluster of polychaete castings or tunnels. Their decalcified section is particularly interesting with regard to ‘a pale eosinophilic array of parallel fibrils apparently forming the shell of the nodule’ (Perry et al., 2008:509). A petrographic section might have been more informative. Sections of the tubes built in sediment by one modern polychaete show minute circumferential layers and particle size gradients (Aller & Yingst 1978) that are perhaps consistent with the ‘shell’ region of the Aqaba fossil. Marine fossil worm tubes from the Lower Oligocene (Goedert et al., 2000), Jurassic to Cretaceous (Hammer et al., 2011; Hilario et al., 2011) and Lower Jurassic (Vinn et al., 2008a) are described in articles that include petrographic sections that might be useful to compare with the Aqaba specimen. Vinn et al. (2008b) describe tube ultrastructure that resembles that in recent polychaete genera. Their Figure 1 would be useful for comparing an etched section of the Aqaba specimen if a scanning electron microscope image were available.

Porter (2010) describes the seawater geochemistry from late Precambrian Ediacaran through Cenozoic Oligocene, comparing organismal deposition of calcite or aragonite, and Taylor et al. (2010) use spectroscopy to determine magnesium and strontium content of polychaete tubes. A chemical analysis of the Aqaba specimen might thus be informative about its geological origins.

Muller (1979) gives a complete description of the taphonomic processes involved in the fossilisation of invertebrates. Considering the complexity of the fossilisation process in marine environments, Boardman et al. (1987) would also aid in the understanding of the various aspects of postmortem and postdepositional change that may have occurred to the Aqaba specimen. This specimen may be a cast of a worm tube that represents only postdepositional features with no internal structure. However, the diagenetic events related to lithification, filling, crystallisation and/or replacement can be evaluated, and they would not occur in a human parasite.

This fossil could have been collected by the buried individual or his friends, and it could have been deposited intentionally with the burial as grave goods or in clothing. Mayor (2000) has shown that many fossils were objects of curiosity or mythology in the ancient world. The Aqaba fossil could have served as a touch stone, an amulet or a decoration. Making this argument would require specific identification of the fossil and careful study of the burial soil to exclude the more likely interpretation of the fossil as a local soil inclusion at this coastal site.

The study of trace fossils, or ichnology, intersects with paleopathology in several interesting ways. The founder of our field, Roy Moodie, was an invertebrate paleontologist by training, and he was particularly interested in ichnology (Moodie, 1928). In his search for the earliest evidence for disease, he diagnosed a Silurian crinoid with ‘hypertrophy…due…to incrusting organisms or worm tubes’ as an example of parasitism (Moodie, 1923:32). Trace fossils have stimulated fascinating folklore and archaeology (Mayor & Sarjeant, 2001), and they have become a specialty or sorts in paleontology.

Everyone who excavates burials would hope to be as broadly prepared in natural history as was Roy Moodie. Barring that, we need to make use of our colleagues in other disciplines. A first question in the field ought to be whether any particular find is a body part or not. Although we need to search systematically for unusual calcified or ossified tissues, as Perry et al. (2008) recommend, we also need to maintain some skepticism with regard to misinterpreting finds that are normal constituents of soil. Perry and colleagues have contributed an exhaustive and extremely useful review of abdominal soft tissue calcifications. However, the object they describe is not pathological, and it is neither a human tissue nor a human parasite.

‘The smallest worm will turn being trodden on,And doves will peck in safeguard of their brood.’Shakespeare: Henry VI

References

  1. Top of page
  2. ABSTRACT
  3. References
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