This is an Ancyloceras (Audiloceras) ammonite. It has what is known as heteromorph shape. While most ammonites have spiral sheels that retain the same shape throughout growth (homeomorph), a major group of ammonites, the Ancyloceratina, emerged during the Late Jurassic that had uncoiled shells and was called heteromorph ammonites (different-shaped). While little is known of their mode of life, was uncoiled shells would have precluded fast swimming. They may have wobbled their way through the water column with out-splayed tentacles, sweeping whatever came within their reach into their hungry mouths. As all ammonites, these went extinct at the end of the Cretaceous.