Didymoceras navarroensis

Didymoceras navarroensis is an extinct heteromorph ammonite species from the upper Campanian to lower Maastrichtian (83.5 to 66 million years ago). It possessed a large shell that twisted loosely left or right, gradually enlarging until it suddenly expands right before the opening with flattened upper and lower sections. The dorsal surface of the shell is ornamented with two twisting series of nodes, one near the center and the other nearer the center of the spiral. Ridges are also present, usually indistinct on the upper surface but becoming more prominent and split into two in between the nodes.