Hildoceras Bifrons ammonite fossil - Whitby, North Yorkshire Jurassic Coast

Ammonite shell fossil found near Whitby, North Yorkshire on the Jurassic Coast

Squared top with a strong keel bordered either side by a groove are distinctive features.  Spiral groove (indentation on the side of the whorls) and sloping umbilical wall (bottom edge of the whorl).  Curved sickle-shaped ribs, which are strongest above the spiral groove.  Can reach large size (over 6 inches), although 4 inches or less more common. A more slender and fine ribbed form/species Hildoceras semipolitum (Buckman, 1902) can be found at Ravencar.

Actual ammonite size: 8.3cm 

Age (lithology): Upper Lias; Toarcian; Bifrons zone; Fibulatum and Crassum subzones.

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

Occurrence:  Common