Mironenko Aleksandr (2015) Wrinkle layer and supracephalic attachment area: implications for ammonoid paleobiology. Bulletin of Geosciences, 90(2), 389-416

Abstract

Wrinkle layer and supracephalic attachment area: implications for ammonoid paleobiology.

Soft-tissue attachment scars of two genera and four species of Late Jurassic craspeditid ammonites from the Russian Platform are described. A previously suggested relationship between lateral attachment scars and ammonoid hyponome is confirmed, however, a new interpretation is proposed for dorsal attachment scars: they could have been areas not only for attachment of the dorsal (nuchal) retractors, but also of the cephalic retractors. The new type of the soft-tissue attachment—anterior lateral sinuses, located between the lateral attachment scars and the aperture of the ammonite body chamber is described. Enclosed elliptical or subtriangular areas in apertural parts of the anterior lateral sinuses were found for the first time. Their presence and location suggest that this structure could have been used for attaching the funnel-locking apparatus, similar to those of coleoids. A transformation of shape and position of lateral attachment scars through the evolution of the Late Jurassic craspeditid lineage starting from platycones (Kachpurites fulgens) to keeled oxycones (Garniericeras catenulatum) is recognized.

Synopsis

The article is devoted to the findings of the so-called "wrinkle layer" on the shells of Callovian and Oxfordian ammonites in Central Russia. This is the first publication about the wrinkle layer of the shells of Jurassic ammonites from Russia. A new term "supracephalic attachment area" is introduced in the article, which denotes a portion of the wrinkle layer located outside of the ammonite body chamber in front of the aperture. The article discusses the paleobiological implications of a wrinkle layer and syn vivo orientation of ammonite shells in the water column, as well as the possible structure of their soft body.

Keywords

Ammonoidea, Craspeditidae, Kachpurites, Garniericeras, attachment scars, paleobiology, Jurassic, Russia

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