Lower and upper jaws of the Early Permian goniatitid ammonoids

Ammonoids – cephalopod molluscs with external shells that existed from the EarlyDevonian up to the end of the Cretaceous – had well-developed jaws. During ammonoid evolution, several different types of their jaw apparatus arose, the study of which is of undoubted interest since it allows researchers to draw conclusions about the feeding strategies of ammonoids and their position in trophic chains. However, there is alack of findings relating to the evolution of ammonoid jaws during the Permian. Herewe describe a collection of almost thirty of cephalopod jaws from the Divjinskian Formation (Artinskian Stage, Cisuralian, Lower Permian), from the Sverdlovsk regionof Russia. Most likely, these jaws belong to goniatitid ammonoid Uraloceras, the most abundant cephalopod mollusc in the Divjinskian (Divya) Formation. Uraloceras lower jaws are typical ammonoid anaptychi which have a rounded, wide and convex shapewith smooth or slightly ribbed surface. They have a large inner lamella with a trapezoidal platform in the central part. One of the jaws bears a possible bite trace of a predator orscavenger. The upper jaws, described here for the first time, are slightly smaller than the lower jaws, their shape is narrow and pointed. Originally, both jaws were completely organic without calcareous elements. The absence of sculpture, consisting of frequent ribs and growth lines, characteristic of the more ancient Carboniferous goniatitid jaws, makes the jaws of the Uraloceras closer to the structure of the jaw apparatus of Triassic ammonoids. Judging by the pointed shape of the tips of both jaws, Uraloceras were active predators