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Remarks on the possible function of the apophyses of the Middle Jurassic microconch ammonite Ebrayiceras sulcatum (Zieten, 1830), with a discussion on the palaeobiology of Aptychophora in general

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Abstract:

A newly found adult specimen of the aptychophoran ammonite microconch Ebrayiceras from the Lower Bathonian of Sengenthal, Oberpfalz (Germany, Bavaria) exhibits completely preserved prominent peristomal apophyses. The specimen is described and figured in some detail in order to demonstrate the extreme constriction of the aperture by the apophyses. These peristomal lappets are interpreted to represent a kind of protection shield, particularly against intersexual cannibalism during mating when the ammonite had to expose soft parts. It can be assumed that the adult Ebrayiceras was able to protrude only small brachia and hyponome through the minute apertural openings which raises the question how the animal could gather sufficient food. We suggest the possibility of mucous web feeding in Ebrayiceras as is e.g. the case in modern holoplanktic and planktotrophic thecosome gastropods. Such a feeding strategy would allow the ammonite to capture fair amounts of small planktic prey using relatively short brachia and without the necessity of protruding its head. It must be concluded that only because of such or a similar feeding strategy the extreme peristomal constriction of Ebrayiceras was possible. It is speculated that other aptychophoran ammonites also used a mucous web to capture planktic prey.

Keywords: APTYCHOPHORA; BEHAVIOUR; MICROCONCH AMMONITES; PALAEOBIOLOGY; THECOSOMATA

Document Type: Research Article

DOI: http://dx.doi.org/10.1127/0077-7749/2009/0026

Publication date: March 1, 2010

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