The food of the miosirenAnomotherium langenwieschei (Siegfried) — indirect proof of seaweed or seagrass by xenomorphic oyster fixation structures in the Upper Oligocene (Neogene) of the Doberg, Bünde (NW Germany) and comparisons to modernDugong dugon (Müller) feeding strategies

Abstract

The palaeoecology of two large oyster species of the Doberg (North Germany) are described. The Upper Oligocene large oysterPycnodonte (Crenostrea) callifera (Lamarck 1819) has unusual fixation structures in the form of large elongated negative impressions on the right and convex xenomorphic structures on the left valve. The heavy oysters ofP. (C.)callifera must have already been attached in their larval stage to the base of stapes of macro algae on which they sometimes built colonies with several individuals. Balanids and serpulids on the algae were overgrown. On the second medium-sized and flat oyster speciesOstrea (Ostrea) cf.digitalina (Eichwald 1830) of the Upper Oligocene, different xenomorphic structures are present. These are thin elongated fixation negatives with concentric rings. The radial sculptured oysters must have been attached onto the Upper Oligocene seagrass rhizomes, such as recentOstrea species do in the Mediterranean Sea.Ostrea started the attachment in the larval stage on the roots in between sea grass meadows which covered the shallow coastal shore seafloor. Both plant groups, seagrass and brown macroalgae, indicate very shallow and moderately warm water conditions and were important food plants of the Oligocene miosirenAnomotherium langenwieschei (Siegfried 1965) that was found at the Doberg as a nearly complete skeleton. Another skeleton of this species was found within the “Middle Oliogocene, uppermost Rupelian” in the Kassel Bay at Schaumburg-Hoof; and finally a single massive rib find of late Lower Oligocene age (Bohlener Schichten) proves for the first time this miosiren in the Leipzig Bay was present during the latest Rupelian. An overlapping of both species can be proved at this time (uppermost Rupelian) with finds of both north of the Rhenish Massif, and in the Leipzig Bay. In Espenhain both species occur in the Bohlener Schichten. Here the only known articulated skeleton remain ofHalitherium schinzii (Kaup 1838) can be reported. This eosirenia was possibly hunted by a large shark, most probablyIsurus of which several teeth were found in-between the disarticulated skeleton. At the minimum it was strongly scavenged, which is indicated by many shark bite scratch marks found all over the ribs and vertebrae. The north Rhenish Massif and western Kassel Bay was different with its Upper Oligocene carbonate environment; only here miosirenia found seagrass as their main food source. In the other siliciclastic dominated Cologne Bay and Leipzig Bay the eosireniaHalitherium could have fed during the Rupelian on seaweeds, but possibly also on other food sources.