Bite traces of a large, mosasaur-type(?) vertebrate predator in the lower Turonian ammonite Mammites nodosoides (Schluter, 1871) from the Czech Republic

A specimen of the acanthoceratid ammonite Mammites nodosoides from the lower Turonian of the Bohemian Cretaceous Basin shows signs of having been preyed upon by a reptile, probably with a mosasaur-like dentition. Based on these traces, a new ichnotaxon, Nihilichnus quadripertitus Mikulas, isp. nov., is erected. Several bite traces are arranged into two convergent, straight rows, which would rule out sauropterygian reptiles or fishes as agents. Jaw margins appear to contour the ammonite aperture, suggesting an attack directed at the apertural part with the head and arm crown. The lethal nature of the bite(s) inflicted is supported by the crushed anterior, albeit not anteriormost, portion of the body chamber. Spacing, size and angle of these traces, as well as the angle of convergence between both rows would suggest that the agent was a medium-sized (up to 6 m) member of the marine lizard family Mosasauridae, and more specifically, of the subfamily Tethysaurinae. However, a representative of another closely related subfamily, the Yaguarasaurinae (which includes the genus Romeosaurus), cannot be ruled out. The bite marks on the present ammonite shell contribute to a palaeoecological evaluation of tethysaurines (in particular with regard to food adaptations) and to a better picture of the palaeogeographical distribution of early Turonian mosasauroids across central European shelves. (c) 2023 Elsevier Ltd. All rights reserved.