In situ-preservation of jaws in the upper Turonian acanthoceratid ammonite Prionocyclus germari (Reuss, 1845): Palaeobiological and taphonomic aspects

Abstract

Cephalopod mandibles are rare in the Bohemian Cretaceous Basin (BCB) of Central Europe, occurring only as isolated jaw elements, the sole exception being a specimen of Yezoites bladenensis found with a lower jaw in situ in the second half of the 19th century. Here, we present a second record, a specimen of the acanthoceratoid ammonite Prionocyclus germari (Upper Cretaceous, upper Turonian). The ammonite preservation shows similarities to ammonoids from Solnhofen-type Lagerstätten, including phosphatised siphuncles, while the flattened ammonite conch is poorly preserved or fully dissolved. The lower jaw of P. germari is referred to the genus Praestriaptychus. Linking the jaw apparatus with an index ammonite taxon of the uppermost Turonian fills a gap in our knowledge of Upper Cretaceous acanthoceratoid ammonite jaw anatomy. The preservation of altered (secondarily carbonised) organic matter has been revealed by Raman spectroscopy analysis at the tip of the aptychus.The associated fauna and flora, consisting of complete crustaceans, fish, chondrichthyans and gymnosperm plant remains, reflect an unusual and unique preservational/taphonomic window within the BCB.