The findings of fossilized ammonite soft tissues are extremely rare, so each specimen may be important for understanding the anatomy of these cephalopods. This paper deals with soft tissue fragments and imprints preserved in the rear part of the body chamber of the Middle Jurassic ammonite Cadoceras stupachenkoi from Central Russia. At the base of the body chamber of this ammonite in front of the last septum, a mantle fragment with clearly visible longitudinal fibers and imprints of the palliovisceral ligament are preserved. In front and slightly to the side of the mantle fragment, a small area with branched structures is located; probably, these structures are fragments of gills. In general, the structure of the soft tissues in the rear part of the ammonite body looks very similar to that of modern nautilids, with one exception: mantle fibers are not directed forward as observed in Nautilus, but to the mid-ventral line, probably to the ventral muscle.
The article is devoted to the discovery of the remnants of soft tissues (phosphatized fragments of mantle muscles and presumably of gills) in the body chamber of the Middle Jurassic (Lower Callovian) ammonite Cadoceras stupachenkoi Mitta from the Unzha river (Kostroma region, Russia). The finding described in this article is to date the second known example of a fossilized ammonite mantle.
Ammonoids, Middle Jurassic, Soft tissues, Cadoceras, Russia