Healed Shell Fractures

Nonlethal injuries are observed in specimens of all ammonite species from the Dubki Quarry. These injuries have been interpreted as originating as bites or some other form of damage to the ammonite shell or mantle. These pathologies occur as irregularities of the shell in the form of ruptures, scars, wrinkles, folds, scratches, and displaced ribs. They prove that not only did the ammonites have to contend with the infestation of epizoa, but they also had to survive attacks from a variety of predators such as fish, reptiles, and other cephalopods (animals commonly cited as modern cephalopod predators). The injuries in this fauna are all consistent with healed pale-opathologies as seen in many publications (for example, Landman and Waage, 1986; Bond and Saunders, 1989; Keupp, 1976, 1996, 2000; Hengsbach 1996; and others).

Hengsbach (1996) listed a fairly complete summary of most of the previous work on pathological ammonites. His use of the German forma and aegra names to describe the healed ammonite pathologies was not new, but rather a comprehensive overview of the previous work done by so many paleopathologists. The terms forma meaning "form" and aegra meaning "sick," though appropriate, are very confusing when used in conjunction with the healed wounds found on pathological ammonites. I have chosen to use other names for these injuries, while maintaining the original references for the forma names.

Kröger (2002) showed several examples of nonlethal injuries in ammonites. He noted six different types of breakage and repair to the ammonite shell and assigned names from medical terminology. He documented the high incidence of injuries in the genus Quenstedtoceras, among many other genera. But because all of the specimens utilized in his paper were from the collection of H. Keupp, who selectively collects such specimens, there was naturally a high incidence of pathological ammonites. Kröger's study dealt with the percentage of different types of sublethal predation, and the most common breakage to the shell. The most common breakage or injury is damage to the aperture of the ammonite. Only a small percentage of shell damage appears as a deeper injury to the flank or venter.

Fig. 16.13 (a) Quenstedtoceras (L.) lamberti showing large-repaired rupture (BHI-5424) (x0.8). (b) Eboraciceras showing large-repaired rupture and shell regrowth (BHI-5499) (x0.8). (c) Recent Nautilus showing a healed rupture (BHI-5603) (x0.35).

The percentage of sublethal injuries (as well as deformities caused by epizoa) in the fauna from the Dubki Quarry is difficult to calculate. The specimens used in this study were chosen out of perhaps ten to twenty thousand, or more. Bond and Saunders (1989) reported a 15% incidence of shell injury and repair among Late Mississippian ammonites from the Imo Formation of northwest Arkansas. P. L. Larson (1984) reported that the number of pathological specimens in the family Scaphitidae from the Fox Hills Formation ranged from 15% (Hoploscaphites nicol-letii Range Zone) to 46.7% (Jeletzkytes nebrascensis Range Zone). Landman and Waage (1986) noticed a 10% incidence of shell abnormalities from the Hoploscaphites nicolletii Zone and 25-40% from the Jeletzkytes nebrascensis Zone based on their ammonite collection. Judging from the thousands of specimens seen and reported from the Saratov locality, it is estimated that perhaps only 10% of the Saratov fauna had any sort of deformities resulting from healed fractures or attached bivalves.

There are several different pathologies that occurred in all ammonite species, as a result of survived predatory attacks. The following list includes some of the different forms of scarring in the ammonites that have been found at the Dubki Quarry.

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