Material

The Quenstedtoceras (L.) lamberti Zone lies in the uppermost upper Callovian of the Upper Jurassic. The fauna from this zone was deposited in clays and marls in the central portion of the Russian Platform (Meledina, 1988). The Q. (L.) lamberti Zone directly overlies the Peltoceras athleta Zone, corresponding to the western European ammonite zones (Meledina, 1988). The ammonite fauna in the Q. (L.) lamberti Zone is also quite similar to that of the stratotype described from Europe. In addition to Quenstedtoceras, other ammonite genera in the Dubki Quarry include Eboraciceras, Grossouvria, Hecticoceras, Kosmoceras, Peltoceras, Prorsiceras, Cadoceras, and Rursiceras (?). Further information on the geology of the area can be found in Aleksejev and Repin (1986).

Residing within the collections of the Black Hills Museum of Natural History and Black Hills Institute of Geological Research, Hill City, South Dakota, are approximately 1,100 ammonite specimens collected from the Dubki Quarry, a commercial clay quarry and brickyard, near Saratov, Russia. These collections contain nearly 1,000 specimens of Quenstedtoceras (Lamberticeras) lamberti and 100 mixed specimens of Eboraciceras, Peltoceras, Kosmoceras, Grossouvria, Prorsiceras, Cadoceras, and Rursiceras all collected from the same zone during 2001 and 2002. There are 167 specimens of Q. (L.) lamberti and 89 specimens of other ammonite genera that exhibit a wide range of healed injuries due mostly to predation. A total of 655 specimens of Q. (L.) lamberti display very unusual deformed growth of the shell (15 of these also exhibit healed predation scars and are included in the above count). There are 48 Q. (L.) lamberti with an unusual distortion, where the ammonite grew in a tilted manner due to an unknown cause. A total of 43 Q. (L.) lamberti exhibit small depressions in the venter, believed to be due to the attachment of

Fig. 16.1 (a) Placunopsis (9 x 10mm) on umbilicus of Quenstedtoceras (L.) lamberti (BHI-5360). (b) Placunopsis (7 x 9.7mm) on venter of Q. (L.) lamberti (BHI-5345). (c) Ostrea (?) (15 x 19.8mm) on flank of Q. (L.) lamberti (BHI-5336). (d) Ostrea (19.5 x 19.5mm) on flank of Q. (L.) lamberti (BHI-5469). (e) Placunopsis (11.5 x 15mm) on Q. (L.) lamberti (BHI-5306). (f) Four Placunopsis (largest 12.5mm; smallest 8.3 x 10mm) on flank, venter, and umbilicus of Q. (L.) lamberti (BHI-5340).

Fig. 16.1 (a) Placunopsis (9 x 10mm) on umbilicus of Quenstedtoceras (L.) lamberti (BHI-5360). (b) Placunopsis (7 x 9.7mm) on venter of Q. (L.) lamberti (BHI-5345). (c) Ostrea (?) (15 x 19.8mm) on flank of Q. (L.) lamberti (BHI-5336). (d) Ostrea (19.5 x 19.5mm) on flank of Q. (L.) lamberti (BHI-5469). (e) Placunopsis (11.5 x 15mm) on Q. (L.) lamberti (BHI-5306). (f) Four Placunopsis (largest 12.5mm; smallest 8.3 x 10mm) on flank, venter, and umbilicus of Q. (L.) lamberti (BHI-5340).

epizoa on the venter or the result of a healed bite. Only 95 specimens of Q. (L.) lamberti in this collection exhibit little to no shell deformation.

While about 25% of these ammonites display healed, predatory scarring, 60% exhibit some very unusual and grotesque abnormalities from a nonpredatory source. These bizarre deformities appear to be the result of an infestation of i mmature bivalves attached to the shell of the ammonite. Originally, the author believed the epizoa were articulate brachiopods; however, H. Feldman (2005, personal communication) confirmed that they were not brachiopods, but rather bivalves. D. Seilacher finally identified the majority of the epizoa as the bivalve Placunopsis along with some minor Ostrea (2005, personal communication).

Although this collection contains eight different genera of ammonites with healed injuries, only Quenstedtoceras (L.) lamberti seems to have been utilized as a host for this infestation of epizoa. It appears that, in most cases, the epizoa were not removed by the ammonites and, as a result, the ammonites grew over and/or around their "guests." Some bivalves grew quite large relative to the size of their ammonite hosts, and this resulted in some very bizarre and erratic deformities to

Fig. 16.2 (a) Serpula on flank and venter of Quenstedtoceras (L.) lamberti (BHI-5440) (xl). (b) Serpulids lying across umbilicus, flank, and venter of Q. (L.) lamberti (BHI-5442) (x0.7). (c) Serpulids crossing over the venter of Q. (L.) lamberti (BHI-5597) (xl).

the ammonites. The ammonite shell became further distorted when the animal tried to compensate for the additional weight and uneven distribution of the bivalves.

It is unknown why the bivalves attached themselves to the ammonites. It is possible that Quenstedtoceras (L.) lamberti were being used as carriers by the bivalves to migrate into other areas of the sea, as documented by Allen (1937) for extant articulate brachiopods attached on mobile gastropods and scallops. The ammonite fauna from the Dubki Quarry was collected in marl or clay (material suitable for making bricks). Deposition of these clay particles suggests a calm, deep marine environment (Reineck and Singh, 1980). The ammonite specimens contain a great deal of pyrite filling and replacement in the phragomocone, indicating that they were buried in a reducing or oxygen-deficient environment (Reineck and Singh, 1980). Because the ammonites would have been unable to survive in this low oxygen environment, they must have been living in the water column, well above the bottom, although (to my knowledge) there has not yet been any isotopic studies of Quenstedtoceras (L.) lamberti to determine what water depth they inhabited. They were most likely active swimmers, though it is not known how well they were able to swim.

As stated before, approximately one thousand ammonite specimens from the Dubki Quarry were used in this study. That is a small portion of the total number of ammonites collected from this site to date. S. Baskakov (personal communication, February, 2003) estimated that between 50,000 and 70,000 ammonite specimens were collected from this locality by the Spring of 2003, and thousands more since then. These numbers represent a very small percentage of the ammonites originally deposited in this particular stratum, as large excavations have previously taken place in the quarry to mine the clay (and the ammonites) for the production of industrial bricks. Of all the genera of ammonites identified from this locality, only Quenstedtoceras (L.) lamberti exhibits deformations due to attached epizoa, while all species from the locality exhibit sublethal pathological scarring due to bites or predation.

It is interesting to note that there are no complete or even nearly complete specimens of Quenstedtoceras (L.) lamberti in this entire collection. All of the specimens from this site consist primarily of phragmocones; partial body chambers

Fig. 16.3 (a) Protuberance extruding from venter o/Quenstedtoceras (L.) lamberti (BHI-5379) (xl). (b) Two small swellings on the venter of Q. (L.) lamberti (BHI-5380) (x0.9). (c) Protuberances extruding from the venter of Q. (L.) lamberti (BHI-5372) (xl). (d) Protuberances extruding from the venter of several Q. (L.) lamberti specimens (BHI-5366 left, BHI-5367 top, BHI-5335 right, BHI-5374 bottom) (x0.5). (e) Flattened swellings on the venter of Q. (L.) lamberti (BHI-5391) (xl.5).

Fig. 16.3 (a) Protuberance extruding from venter o/Quenstedtoceras (L.) lamberti (BHI-5379) (xl). (b) Two small swellings on the venter of Q. (L.) lamberti (BHI-5380) (x0.9). (c) Protuberances extruding from the venter of Q. (L.) lamberti (BHI-5372) (xl). (d) Protuberances extruding from the venter of several Q. (L.) lamberti specimens (BHI-5366 left, BHI-5367 top, BHI-5335 right, BHI-5374 bottom) (x0.5). (e) Flattened swellings on the venter of Q. (L.) lamberti (BHI-5391) (xl.5).

are rare. Apparently, either the body chambers were not filled with a stable enough host material, or postmortem predation did away with the body chambers before preservation. The large numbers of Q. (L.) lamberti from this site most likely represent mass spawning deaths over several years or generations. This is one of the largest known collections of a single ammonite species from a single site with such a large percentage of deformities resulting from the infestation of epizoa. All of the ammonites illustrated in this paper reside in the collection of the Black Hills Museum of Natural History, 117 Main St., Hill City, South Dakota and are identified by the prefix BHI.

Was this article helpful?

0 0

Post a comment