Flank Attachments

Of 655 known deformities caused by epizoa, 61 or about 10% have epizoa attached to the flank. This number is somewhat significantly lower than ventral attachments yet still a much larger place for attachments than the umbilical placements.

Deformity. Bivalves attached to the flanks caused the ammonite to suffer a crooked and twisted venter that deviates from the center (Fig. 16.9a-c). This is similar in appearance to the human deformity called "scoliosis," which means "a lateral curvature of the spine." Ammonite shell distortions, mainly the result of

Fig. 16.9 (a) Curvature of the venter on Quenstedtoceras (L.) lamberti (BHI-5384) (xl). (b) Severely deformed Q. (L.) lamberti, resulting from attached epizoa (BHI-5338) (xl). (c) Another severely deformed and twisted Q. (L.) lamberti (BHI-5466) (x0.8).
Fig. 16.10 (a) Placunopsis (?) (7.5mm across) near umbilicus of Quenstedtoceras (L.) lamberti (BHI-5613). (b) Placunopsis on flank and venter of Q. (L.) lamberti (BHI-5340). (c) Placunopsis (9.5 x 13.7mm) on flank and venter of Q. (L.) lamberti (BHI-5305).

healed bites, resembling the deformities seen from the Dubki Quarry have been described as forma undatecarinata by Heller (1958), and illustrated by Hengsbach (1979: Fig. 16.8b), and as forma aegra undatispirata by Keupp and Ilg (1992) and Keupp (1995, 1996, 2000). Landman and Waage (1986) referred to a similarly twisted venter as "Morton's syndrome," although they did not believe the deformity was caused by an injury. Those ammonites described as having "Morton's syndrome" most likely suffered from unsuccessful predation early in their life.

Cause. Checa et al. (2002) described this deformity as "zigzag." This deformity occurred when the epizoon attached itself to the flank of the ammonite (Fig. 16.10a-c). Depending upon the size and number of animals that attached to the shell, this regularly resulted in grotesque and monstrous deformities. Sometimes there were many of these pelecypods, and commonly they grew quite large on the flanks of the ammonites. In attempting to cover the epizoa, the ammonite had to deal with the ever enlarging and uneven weight distribution caused by the size of these epizoa and its own malformed shell growth. As a result, the ammonite became twisted, with an extremely crooked venter that bent to one side and sometimes back again (Fig. 16.10b, c).

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