Harpoceras ammonite triple fossil - Whitby, North Yorkshire

Ammonite fossil from Whitby, North Yorkshire

Compressed (flattened) discus shaped ammonite with strong sharp keel on the top.  Strong and distinctive falcate (wavy) ribs, spiral groove (indentation on the side of the whorls), and undercut umbilical wall (bottom edge of the whorl).  Can reach large size (over 6 inches), although 4 inches or less more common.

Age (lithology):  Upper Lias; Toarcian; Falciferum zone; Falciferum subzone.

Largest ammonite size: 7.2cm 

Distribution: Port Mulgrave, Runswick, Kettleness, Sandsend, Hawsker.

Occurrence:  Relatively common